Centrifugal Pump Selection for Water and Wastewater Treatment

Section 1

Selection wizard

Describe the duty and get a first-pass specification: machine type, speed and specific speed, impeller, materials, seal, drive and motor size, with the reasons and the checks still to do. Choosing a liquid loads its typical properties. Change any of them.

Liquid and service

Flow at duty L/s

Total head m

Installation

Supply frequency

Liquid properties

Total solids %

Chloride mg/L

Temperature °C

Conditions Rags, wipes or fibre Grit or abrasives Shear-sensitive biomass Entrained gas Scaling or crystallising Explosive atmosphere Drinking water contact

Recommended machine

The wizard applies the rules of thumb set out on this page. Use it to start a datasheet and to check a proposal, then confirm against certified curves, the system curve envelope and the supplier's materials data.

Section 3

Hydraulic fundamentals that decide the selection

A centrifugal pump adds energy by accelerating liquid through a rotating impeller and converting that velocity into pressure in the casing. Everything about selection follows from four curves and one margin.

The four curves

Curve	What it plots	What it governs	Selection rule of thumb
Head–capacity (H–Q)	Head developed against flow, at a stated speed and impeller diameter	Where the duty point lands when crossed with the system curve	Select the duty at or slightly right of the best efficiency point (BEP) when new, because wear and pipe ageing both move the operating point to the left, back toward BEP
Efficiency	Pump hydraulic efficiency against flow	Energy cost, heat into the liquid, and reliability	Target 100–110 % of BEP flow; stay inside 70–120 % (the preferred operating region of ANSI/HI 9.6.3)
NPSH required	Absolute head needed at the suction flange to keep 3 % head loss from cavitation	Whether the pump cavitates; suction geometry and elevation	Available NPSH must exceed required NPSH by a real margin, not by zero
Power	Shaft power against flow	Motor rating, VFD rating, cable and starter	For most process pumps, size the motor non-overloading across the whole curve, not just at duty

Head, not pressure

A centrifugal pump imparts head, measured in metres of the liquid being pumped. The pressure it produces depends on density; the head does not. Pump 1.05 SG digested sludge instead of water and the same impeller at the same speed gives the same metres of head but 5 % more pressure and 5 % more absorbed power.

Total head H = (z₂ − z₁) + (p₂ − p₁)/ρg + (v₂² − v₁²)/2g + h_f

In treatment plants the static term usually dominates on lift stations, force mains and high-service pumping, while friction dominates on membrane feed loops, recirculation loops and filter backwash. Which one dominates changes everything about whether a variable speed drive saves energy — see Section 13.

Build the system curve as an envelope, not a line

A single system curve is a fiction. Static head moves with wet-well level, reservoir level and tide. Friction moves with pipe ageing, biofilm, and how many duty pumps run in parallel. Always draw at least two curves and check the pump is acceptable at both extremes.

Minimum-resistance case: lowest static lift, new pipe (Hazen–Williams C = 140–150 for lined ductile iron or HDPE). This is where the pump runs furthest right — check motor overload, NPSH and cavitation.
Maximum-resistance case: highest static lift, aged pipe (C = 100–120 for a sewage force main with slime growth), partially closed valves. This is where the pump runs furthest left — check minimum continuous stable flow, temperature rise and radial thrust.
For wastewater force mains, add an allowance for slime: many designers use C = 120 for design and 140 for the check on the runout case.

Total head calculator — Darcy–Weisbach with minor losses

Flow L/s

Internal diameter mm

Pipe length m

Roughness mm

Sum of fitting K values

Static lift m

Residual pressure needed m

Kinematic viscosity mm²/s

Velocity–

Reynolds number–

Friction factor–

Pipe friction–

Fitting losses–

Total head–

Velocity guidance: suction 0.9–1.8 m/s, discharge 1.5–3.0 m/s, sewage force main 0.75–2.4 m/s for self-scouring.

NPSH: the margin, not the match

NPSH available is fixed by the installation. NPSH required is a property of the pump at that flow, and it is defined at the point where the pump has already lost 3 % of its head to cavitation — damage begins well before that. Matching NPSHa to NPSHr is not a pass.

NPSHa = (p_atm − p_vap)/ρg + z_suction − h_f,suction

ANSI/HI 9.6.1 sets the margin ratio (NPSHa / NPSHr) by application and suction energy: roughly 1.1–1.3 for low suction energy, rising to about 1.7–2.5 for very high suction energy, always with a minimum absolute margin. A common design floor for ordinary water and wastewater duties is the larger of 1.0 m or 1.3 × NPSHr. High suction energy pumps — large double-suction units, high-speed multistage, seawater intakes — need the upper end of the range, and suction specific speed should be kept below about 11 000 (US units) or 213 (metric).

NPSH available and margin check

Site altitude m above sea level

Liquid temperature °C

Specific gravity

Liquid level above impeller eye m, negative if below

Suction friction loss m

NPSH required by pump m

Vessel pressure above liquid bar g, 0 if open

Atmospheric head–

Vapour pressure head–

NPSH available–

Margin–

Margin ratio–

–

Specific speed sets the impeller shape

Specific speed is a shape number calculated at the best efficiency point. It tells you, before you open any catalogue, whether the duty wants a narrow radial impeller or a propeller. Low-head, high-flow recirculation duties — return sludge, nitrate recycle, membrane tank recirculation — sit at high specific speed, which is exactly why a standard end-suction pump is the wrong machine for them.

n_q = n √Q / H^0.75 (rpm, m³/s, m) · N_s,US = n √Q / H^0.75 (rpm, US gpm, ft) ≈ 51.6 × n_q

Specific speed and impeller type

Speed rpm

Flow at BEP L/s

Head at BEP m

Stages

Suction eyes

Metric n_q–

US N_s–

Impeller geometry–

Attainable efficiency band–

–

Indicative ranges. Attainable efficiency also falls sharply below about 20 L/s regardless of specific speed, because clearances and surface finish do not scale down.
n_q (metric)	N_s (US)	Impeller	Head per stage	Typical treatment duty
8–18	400–930	Narrow radial, high outlet-to-inlet diameter ratio	High	RO high pressure, multistage boosters, fire water
18–40	930–2 100	Radial, the classic end-suction impeller	Medium	High-service potable, filter feed, transfer, sewage lift
40–80	2 100–4 100	Francis / mixed flow	Moderate	Raw water intake, large stormwater, low-lift pumping
80–160	4 100–8 300	Mixed flow, bowl or volute	Low	Return activated sludge, filter backwash, effluent lift
>160	>8 300	Axial propeller	Very low, 0.3–4 m	Nitrate recycle, membrane tank recirculation, flood pumping

Affinity laws and their limits

Q ∝ n | H ∝ n² | P ∝ n³ | NPSHr ∝ n^1.5–2

The laws hold well for speed change on a fixed impeller. They hold only approximately for impeller trimming, because trimming a closed impeller changes the relationship between the vanes and the volute. Beyond roughly 10 % trim, efficiency falls about half a point for each further percent removed, and vane overhang can start to cause pressure pulsation. Below about 75–80 % of maximum diameter, ask for a smaller casing instead.

Efficiency is not conserved under speed change either, though it is close over a 2:1 range. It is also not conserved across a system with static head: reducing speed moves the operating point along the system curve, not along a constant-efficiency line, so a pump slowed to 70 % on a high-static system can fall well left of its preferred region even though the affinity laws say power dropped by two thirds.

The minimum flow trap. Every centrifugal pump has a minimum continuous stable flow, typically 10–25 % of BEP for small end-suction pumps and 40–60 % for large high-energy or double-suction units. Below it you get suction recirculation, high radial load, rising bearing and seal temperature, and in closed systems a real risk of flashing. On VFD-driven high-static duties, calculate the speed at which the pump curve stops intersecting the system curve; that is a hard minimum speed, and running below it simply churns.

Section 4

A selection workflow that survives commissioning

Most pump problems in treatment plants are selection problems wearing a maintenance costume. Work the sequence below in order; each step constrains the next.

Define the flow set, not a flow

Write down minimum, average, peak day, peak hour and future flow. For sewage, apply a peaking factor to average dry weather flow — commonly 2.5 to 4 for small catchments, 1.5 to 2.5 for large — then decide separately how wet weather inflow is handled. For biological recycles, express flow as a ratio of plant influent, because it must track influent through the day.
- Nitrate recycle: 200–400 % of influent
- Return activated sludge: 25–100 % of influent for conventional (typically about 50 %), 50–150 % for extended aeration
- Membrane bioreactor recirculation: 300–500 % of permeate flow
- Anaerobic upflow reactor recirculation: set by required upflow velocity, not by load
Fix the duty and standby philosophy before sizing

Two pumps each at 100 % behave completely differently from three at 50 %. Parallel pumps do not double the flow on a friction-dominated system — each added pump contributes less, often only 60–75 % of its solo flow with two running. Draw the combined curve; do not assume additivity. On high-static systems parallel operation works well; on long force mains it barely helps and the pumps run far left of BEP.
Characterise the liquid honestly

Solids size and type, total solids percentage, abrasives, chloride, pH, temperature, dissolved gas, fats and oils, fibre and rag content, sulphide, and whether the liquid crystallises or scales. Rags and wipes, not particle size, are what actually block modern sewage pumps. Ask for a screening basis: a plant with 6 mm screens and one with bar racks at 25 mm need different impellers.
Build the system curve envelope

Minimum and maximum static, new and aged friction, single and multiple pump operation, clean and fouled strainers or membranes. Membrane systems in particular have a system curve that migrates upward between cleans — size the feed pump for end-of-run transmembrane pressure, then check it is not cavitating or overloading on a fresh module.
Choose the pump family from the liquid and the specific speed

Solids and shear decide the family; specific speed decides the geometry within it. If the shape number says axial and the catalogue says end-suction, the catalogue is wrong for that duty.
Select the hydraulic against BEP, then re-check both ends

Aim the design duty at 100–110 % of BEP flow, verify the runout case stays inside the allowable operating region and within motor rating, and verify the maximum-resistance case stays above minimum continuous stable flow. Confirm NPSH margin at the runout flow, not at duty — NPSHr rises steeply to the right.
Specify materials, sealing and bearings for the liquid and the atmosphere

This is where treatment plants lose pumps. Chloride, sulphide, abrasives and intermittent dry running kill far more pumps than hydraulics do. Materials and seal plan should be specified jointly, since a flush plan can rescue a marginal material choice and a sealless design can eliminate the question.
Size the motor and drive, then design the control

Non-overloading motor selection across the whole curve, inverter-duty insulation and shaft grounding if a VFD is fitted, and a control strategy that keeps the pump inside its preferred region across the diurnal cycle. Decide minimum speed, alternation, and anti-ragging or flush cycles here, not during commissioning.
Check the transient, the intake and the noise

Run a surge analysis on anything with more than a few hundred metres of force main or a significant static lift. Check the sump against ANSI/HI 9.8 for submergence, approach velocity and vortex suppression. Confirm vibration acceptance limits and test tolerance class — ISO 9906 grade 1B, 2B or 3B changes what you are allowed to reject.

Oversizing is the default failure. Safety factors compound: a peaking factor on flow, a rounded-up head, a fouling allowance, an aged-pipe allowance, then the next frame size up. The result runs permanently left of BEP, throttled, with high radial load and short seal life, and it costs energy every hour for twenty years. Add margin in one place deliberately and document it, rather than in five places by habit.

Section 5

Pump families and where each one belongs

Treatment plants use perhaps a dozen distinct machine types. Getting the family right matters more than getting the exact model right, because the family determines maintainability, solids handling and the failure mode you will live with.

Family	Configuration	Typical range	Best fit	Avoid when
End-suction, back pull-out	ASME B73.1 / ISO 2858 & 5199, horizontal, frame-mounted	2–250 L/s, 5–90 m	Clean and lightly loaded liquids: filter feed, effluent, service water, chemicals, membrane feed. Standardised dimensions mean interchangeable suppliers.	Raw sewage, grit, sludge above about 1 % TS, or flows needing more than one casing size
Horizontal split case	Double suction, between bearings, axially split	50–3 000 L/s, 15–150 m	High-service potable, raw water transfer, large effluent pumping. Balanced axial thrust, long life, good efficiency, impeller accessible without breaking pipework.	Any solids; also poor with disturbed inlet flow — needs 5–10 diameters of straight suction pipe, and any nearby elbow in a plane perpendicular to the shaft
Vertical turbine / lineshaft	Multistage bowl assembly in a wet pit or can	10–2 000 L/s, 10–250 m	Intakes with varying water level, deep wells, booster cans where NPSH is short. Submerged first stage solves NPSH by geometry.	Abrasive or fibrous liquids; lineshaft bearings and long shafts need alignment discipline and add maintenance access requirements
Submersible non-clog	Close-coupled motor and hydraulic, guide-rail mounted	5–1 500 L/s, 3–60 m	Raw sewage, stormwater, RAS, most wet-well duties. No dry well, no long shaft, motor cooled by the pumped liquid or a jacket.	Where high efficiency at large size matters more than capital cost, or where the liquid is hot and the motor relies on immersion cooling
Dry-pit submersible / vertical non-clog	Submersible hydraulic in a dry chamber, or vertical shaft with motor above flood level	10–800 L/s, 5–50 m	Large influent stations where operators want to touch the pump without entering a wet well, and where flood immunity is required.	Small stations — the civil cost of a dry chamber dominates
Recessed impeller (vortex / torque flow)	Impeller set back out of the flow path; the liquid moves in an induced vortex	5–300 L/s, 3–40 m	Grit slurry, scum, stringy or air-entrained liquids, anything that must pass whole. Solids pass without touching the impeller, so wear and blockage collapse.	Energy matters — efficiency is typically 35–55 %, well below a closed impeller on the same duty
Screw centrifugal	Single helical vane, large unobstructed passage, gentle acceleration	10–1 000 L/s, 3–40 m	Shear-sensitive and solids-laden duties together: anaerobic granular sludge, return sludge, fish, thickened sludge, primary sludge transfer. High efficiency for a solids pump, often 70 %+.	High head per stage is needed, or space is tight — the hydraulic is physically large
Chopper / grinder	Cutter bar and rotating knife at the suction, integral with the impeller	2–200 L/s, 5–60 m	Digester recirculation, scum, thickened sludge, unscreened sewage, pump stations plagued by wipes. Chops rather than passes.	Abrasive grit is present — cutting elements wear fast; also higher power draw and more parts to replace
Axial and mixed flow propeller	Propeller in a tube or bowl, vertical or submersible, often in a draft tube	50–10 000 L/s, 0.3–8 m	Nitrate recycle, membrane tank recirculation, RAS at low lift, stormwater. The only efficient answer to very high flow at very low head.	Head is uncertain or may rise — power rises as flow falls on an axial machine, the opposite of a radial pump, so motors can overload at low flow
Self-priming	Integral priming chamber, pump above liquid level	5–150 L/s, 5–40 m	Temporary and bypass pumping, small sewage stations without a wet-well entry, membrane permeate suction where air is expected.	NPSH is tight in normal running — the priming chamber adds suction losses; also re-prime time matters on intermittent duty
Ring-section / barrel multistage	Several radial impellers in series; horizontal axially split (BB3) or ring-section (BB4) or barrel (BB5), or vertical inline multistage	5–600 L/s, 50–900 m	Reverse osmosis high-pressure feed, long-distance transfer, high-head booster sets.	Any solids at all; also needs disciplined start-up, low-flow protection and thrust bearing attention
Sealless: magnetic drive and canned motor	No dynamic shaft seal; torque through a containment shell	1–100 L/s, 5–120 m	Hazardous and aggressive chemicals: sulphuric acid, hypochlorite, ferric chloride, where leakage is unacceptable.	Dry running or solids — the internal bearings are product-lubricated and fail within seconds without liquid; magnet decoupling on viscous or slurry duties
Slurry pumps	Heavy-section casing, hard metal or rubber-lined, low tip speed, external bearings	5–500 L/s, 5–60 m	Grit classifier underflow, lime slurry, high-abrasive industrial streams.	Efficiency-critical clean duties — heavy sections and generous clearances cost efficiency points

When a centrifugal pump is the wrong machine

Roughly a third of the pumping in a wastewater plant should not be centrifugal at all. Positive displacement wins whenever flow must be independent of pressure, viscosity is high or variable, shear must be minimised, or suction lift is required on a thick liquid.

Service	Why centrifugal struggles	Usual answer
Thickened sludge, 4–12 % TS, to dewatering	Apparent viscosity of hundreds to thousands of centipoise; head requirement varies hour to hour with solids; centrifugal output collapses	Progressive cavity or rotary lobe; hose pump for short runs
Polymer solution dosing	Shear degrades the polymer chain and destroys flocculation performance	Progressive cavity or diaphragm metering, with low-shear activation
Coagulant and acid metering	Needs repeatable volumetric accuracy at very low flow against variable back pressure	Diaphragm metering pump, or peristaltic for slurries
Lime slurry	Settles, abrades and scales; centrifugal needs continuous flush and still wears	Peristaltic hose pump, or progressive cavity with flushed seal
Digested sludge to centrifuge	Feed rate must be steady and independent of downstream pressure	Progressive cavity with flow control, or lobe pump
Small seawater RO trains	High pressure at modest flow puts centrifugal specific speed uneconomically low	Axial piston positive displacement with pressure exchanger

Section 6

Impellers, solids passage and the rag problem

The impeller is the single most consequential choice in wastewater pumping. It sets solids passage, shear, efficiency and how often an operator has to open the pump.

Impeller	Vanes	Solids handling	Peak efficiency	Use for
Closed multi-vane	5–8, shrouded both sides	Clean liquids only	75–88 %	Potable, effluent, membrane feed, service water. Wear rings maintain efficiency over life.
Closed two-vane non-clog	2, shrouded	Sphere passage typically 75–125 mm	65–80 %	Raw sewage where screening is good. Best efficiency among true non-clogs.
Single channel	1, shrouded	Full pipe-bore sphere passage	60–75 %	Sewage with heavy rag content. Inherently unbalanced — needs careful dynamic balancing and robust bearings.
Semi-open / open multi-vane	2–5, one or no shroud	Moderate, adjustable clearance restores performance	65–80 %	Sludge, industrial effluent, abrasives. Front clearance adjustment is a real maintenance advantage.
Self-cleaning swept-back	1–2 with a relief groove in the casing insert	Rags are led along the leading edge and out	70–84 %	Modern sewage stations with wipes. Combines near-closed-impeller efficiency with rag tolerance; the current default for new municipal stations.
Recessed / vortex	Set back in a recess, often partially open	Passes anything the casing passes; very low contact	35–55 %	Grit, scum, air-entrained and stringy liquids. Accept the efficiency penalty for the reliability.
Screw centrifugal	1 helical vane	Very large, gentle passage	70–85 %	Shear-sensitive biomass, granular anaerobic sludge, thickened sludge, RAS.
Cutter / chopper	2–3 with hardened cutting edges	Reduces solids instead of passing them	50–70 %	Digester loops, scum, small-bore force mains, sites with chronic ragging.
Axial propeller	2–4 blades, sometimes adjustable pitch	Moderate; no volute to trap	75–88 %	Very low head, very high flow recirculation.

Rags defeat sphere-passage specifications. A pump rated for 100 mm solids will still rope up on wet wipes, hair and fibre, which braid at the vane leading edge and the shroud. The three effective countermeasures are a self-cleaning or single-channel impeller geometry, fine screening upstream, and a wet-well design that keeps solids in suspension rather than letting them build a floating mat. A VFD that lets the pump loiter at low speed makes ragging worse, not better — specify a periodic full-speed flush cycle and a de-rag reversal routine.

Shear: when moving the liquid damages the process

Several biological duties are harmed by the pump itself. Shear is set principally by impeller tip speed and the number of passes through the pump per unit of process volume.

Activated sludge floc: excessive shear in RAS and mixed liquor recycle breaks floc, worsens settleability and raises effluent suspended solids. Keep tip speed moderate, favour low-speed large-diameter impellers over high-speed small ones, and avoid throttling.
Anaerobic granular sludge (UASB, EGSB, IC): granules are the reactor's entire working capital. Repeated passage through a high-shear impeller erodes them into dispersed biomass that washes out. Use screw centrifugal or low-speed open impellers, run at 700–1 000 rpm rather than 1 450, and take recirculation from the clarified zone where possible.
MBR mixed liquor: shear reduces floc size, and smaller floc blocks membrane pores more readily. High recirculation ratios mean liquid passes the impeller many times per hour, so a modest per-pass shear accumulates. This is a strong argument for axial flow recirculation rather than a centrifugal pump working against an artificially high head.
Polymer and chemically conditioned sludge: once conditioned, do not pump it through a high-shear machine before the dewatering device.

Section 7

Duty sheets, stage by stage

Thirty-eight pumping duties across a combined water and wastewater site. Filter by stage or search, then open a duty for the type, impeller, materials, sealing, control and the specific ways it goes wrong. Switch to the table to compare all of them at once. Flow and head bands are typical municipal ranges, not limits.

Search duty sheets

38 of 38 duties

Summary only. Open a duty for liquid, control and watch-outs. Tags match the plant diagram.
Tag	Duty	Typical range	Pump type	Impeller	Wetted materials	Shaft seal
P-01	Raw water intake from river, canal or reservoir	50–3 000 L/s 8–45 m	Vertical turbine, wet pit	Enclosed mixed-flow bowl	Epoxy-lined iron bowls; bronze or CF8M impeller	Packing or cartridge, external flush
P-02	High-service and distribution pumping	50–2 000 L/s 30–120 m	Split case, double suction	Closed multi-vane	Lined ductile iron; lead-free bronze or CF8M; NSF 61/372	Single cartridge, Plan 11
P-03	Filter backwash	200–2 000 L/s 6–15 m	Vertical mixed flow or large end-suction	Mixed flow	Cast iron; bronze or stainless; NSF 61	Single cartridge
P-04	Seawater intake for desalination	100–5 000 L/s 10–40 m	Vertical turbine or beach-well submersible	Mixed-flow bowl	Super duplex or nickel aluminium bronze	Cartridge, external flush, SiC/SiC
P-05	Raw sewage lift station, submersible	10–500 L/s 8–45 m	Submersible non-clog on guide rail	Self-cleaning single vane	Grey iron; hardened iron or CF8M impeller	Tandem seals in oil, moisture probe
P-06	Storm and combined sewer overflow pumping	100–10 000 L/s 2–15 m	Vertical mixed or axial column pump	Mixed flow or propeller	Cast iron; hardened impeller	Packing or heavy single seal
P-07	Grit slurry and grit classifier feed	5–80 L/s 5–25 m	Recessed impeller or hard-metal slurry pump	Fully recessed	Ni-Hard 4 or 27 % Cr iron; rubber for fine grit	Packing with Plan 32 flush, or double
P-08	Scum, grease and floatables	2–30 L/s 5–25 m	Chopper or recessed; PC when cold and thick	Cutter or recessed	Cast iron; hardened cutters	Double seal with barrier
P-09	Primary sludge withdrawal	2–40 L/s 5–30 m	Progressive cavity or lobe; chopper if thin	Chopper if centrifugal	Cast iron; hardened rotor or impeller	Double seal or flushed packing
P-10	Return activated sludge (RAS)	30–1 500 L/s 1.5–8 m	Submersible mixed flow or screw centrifugal	Mixed flow	Cast iron; CF8M or hardened impeller	Tandem (submersible) or SiC cartridge
P-11	Nitrate recycle / internal mixed-liquor recirculation	100–3 000 L/s 0.3–2 m	Submersible axial in draft tube	Axial propeller	Cast iron; 316 propeller and shaft	Tandem submersible seals
P-12	Waste activated sludge (WAS)	1–40 L/s 5–25 m	Non-clog centrifugal or PC	Two-vane or self-cleaning	Cast iron; CF8M impeller	Double or tandem
P-13	Jet aeration and motive-liquid pumping	20–400 L/s 10–30 m	Dry-mounted non-clog	Two-vane, passage below nozzle size	Cast iron; stainless impeller	Double seal with barrier
P-14	Moving bed and fixed film recirculation	20–600 L/s 2–12 m	Non-clog or mixed flow	Non-clog closed	Cast iron and stainless	Tandem submersible seals
P-15	Anaerobic digester recirculation and heating loop	10–150 L/s 8–30 m	Chopper centrifugal; PC above about 5 % TS	Chopper or recessed	Ductile iron; hardened or 316 parts	Dual pressurised 53B plus Plan 62 quench
P-16	UASB, EGSB and IC reactor feed	10–500 L/s 6–25 m	End-suction or self-priming	Closed or semi-open	316L minimum; 2205 at high chloride or pH below 4	Cartridge with quench
P-17	Granular sludge recirculation and upflow velocity control	50–2 000 L/s 2–12 m	Screw centrifugal at low speed	Single helical vane	316L or duplex	Cartridge; double where gassy
P-18	Digestate transfer and post-digestion storage	5–80 L/s 10–40 m	PC or lobe; chopper if thin	Chopper or recessed	Cast iron; hardened or 316; no copper	Double seal plus quench
P-19	Biogas condensate and foul condensate	0.1–3 L/s 5–25 m	Small self-priming or mag drive	Closed	PP or PVDF, or 316L; no copper	Sealless or double
P-20	MBR membrane tank recirculation	100–3 000 L/s 1–5 m	Submersible axial or mixed flow	Axial or mixed flow	Cast iron; 316 propeller	Tandem seals, moisture probe
P-21	MBR permeate extraction and backpulse	5–200 L/s −5 to +15 m	Self-priming centrifugal or lobe	Closed, suction-rated	316L; EPDM elastomers	Balanced cartridge rated for vacuum
P-22	Ultrafiltration and microfiltration feed	20–500 L/s 15–60 m	End-suction or split case	Closed multi-vane	316L; duplex for seawater	Single cartridge, Plan 11
P-23	Brackish water RO high-pressure feed	10–300 L/s 100–300 m (10–30 bar)	Ring-section (BB4) or axially split (BB3) multistage	Closed radial, staged	316L up to about 1 000 mg/L chloride; duplex 2205 above	Balanced cartridge, Plan 11 or 13
P-24	Seawater RO high-pressure feed	20–600 L/s 550–750 m (55–75 bar)	Barrel BB5 or axially split; piston PD for small trains	Closed radial multistage	Super duplex or 6 % Mo	API 682 cartridge, often dual
P-25	Clean-in-place and chemical cleaning circuits	5–150 L/s 15–50 m	Plastic end-suction or mag drive	Closed	PVDF or PP, or 316L for dilute; EPDM	Sealless preferred
P-26	Thickened sludge to dewatering	1–25 L/s 10–60 m	Progressive cavity or lobe	None (positive displacement)	Hardened rotor; NBR or EPDM stator	Flushed packing or cartridge with quench
P-27	Centrate, filtrate and sidestream return	2–60 L/s 5–30 m	Non-clog centrifugal	Two-vane or self-cleaning	Cast iron; 316; no copper	Double seal plus quench
P-28	Sludge blending and transfer between tanks	5–60 L/s 8–35 m	Chopper centrifugal or PC	Chopper or recessed	Cast iron; hardened parts	Double seal with barrier
P-29	Leachate and landfill gas condensate	1–50 L/s 15–120 m	Borehole submersible or end-suction	Closed, scale tolerant	2205 or super duplex; PP or PVDF when small	Double seal with barrier
P-30	Sodium hypochlorite transfer and dosing	0.05–10 L/s 10–40 m	Diaphragm metering; mag-drive transfer	Closed, PVDF or PTFE	PVDF, PTFE, titanium; no stainless	Sealless
P-31	Ferric chloride, alum and coagulant dosing	0.02–5 L/s 10–40 m	Diaphragm metering or mag drive	Closed, PVDF or PTFE	PVDF, PTFE-lined, titanium or C-276	Sealless
P-32	Lime slurry and powdered activated carbon	0.1–10 L/s 10–40 m	Peristaltic, PC or rubber-lined slurry	Rubber-lined if centrifugal	Natural rubber, high-chrome iron	None (peristaltic) or flushed packing
P-33	Polymer preparation and dosing	0.02–3 L/s 10–50 m	PC, diaphragm or gear pump	None (no centrifugal: shear)	316 or plastic	Packing or single seal
P-34	Sulphuric acid and caustic soda	0.02–5 L/s 10–40 m	Mag drive or canned; diaphragm metering	Closed	Alloy 20 or PTFE-lined (acid); carbon steel or 316 (caustic)	Sealless
P-35	Final effluent, reuse and UV feed	20–2 000 L/s 5–60 m	End-suction, split case or submersible	Closed multi-vane	Cast iron; 316 impeller	Single cartridge, Plan 11
P-36	Plant service water and seal water	2–50 L/s 40–90 m	Multistage booster set	Closed multistage	316	Single cartridge
P-37	Drainage, dewatering and sump pumping	1–50 L/s 5–30 m	Small submersible	Recessed or semi-open	Cast iron or 316	Tandem submersible seals
P-38	Fire water	30–300 L/s 70–120 m	Listed fire pump set (NFPA 20)	Closed	Bronze-fitted cast iron, as listed	Packing

P-01 Raw water intake from river, canal or reservoir 50–3 000 L/s · 8–45 m

Liquid: Surface water with seasonal silt, sand, leaves, algae and mussel larvae. Level varies by several metres between flood and drought.
Pump type: Vertical turbine in a wet pit is the standard answer because the first stage stays submerged as the level falls. Submersible motor column pumps for deep or remote intakes. Horizontal split case in a dry well only where level variation is small and screening is reliable.
Impeller: Enclosed mixed-flow bowl, n_q typically 40–90. Specify a bowl with generous sand tolerance rather than the highest catalogue efficiency.
Materials: Cast iron bowls with fusion-bonded epoxy lining; bronze or CF8M impellers; 416 or 431 stainless shaft with bronze or rubber lineshaft bearings. Move to duplex for brackish or high-chloride river water.
Sealing: Packing with clean-water lubrication, or a cartridge mechanical seal with an external flush from treated water. Open lineshaft designs need water-lubricated bearings above the suction.
Drive & control: Variable speed matched to plant demand; hollow-shaft vertical motor with non-reverse ratchet. Level-based low-level cut-out with a generous submergence allowance.
Watch-outs: Submergence and vortexing during drought level — check against ANSI/HI 9.8, not just the pump's stated minimum. Sand abrasion of bowls and wear rings; specify replaceable rings. Zebra and quagga mussel colonisation of columns. Debris damage after storms. Long column alignment and shaft critical speed.

P-02 High-service and distribution pumping 50–2 000 L/s · 30–120 m

Liquid: Treated potable water, chlorinated, essentially clean.
Pump type: Horizontal split case double suction for the main duty; vertical turbine can pumps where footprint is tight; vertical multistage for small high-head zones. Stage several different sizes rather than one large pump throttled all day.
Impeller: Closed multi-vane, double suction for axial balance and lower NPSHr.
Materials: Ductile iron or cast iron casing with epoxy lining; bronze or CF8M impeller and wear rings; stainless shaft with a sleeve. Every wetted item must carry NSF/ANSI 61 certification, and NSF/ANSI 372 for lead content — this rules out several traditional bronzes.
Sealing: Single cartridge mechanical seal, carbon against silicon carbide, API 682 Plan 11 flush from discharge.
Drive & control: Variable speed on lead pump with fixed-speed lag pumps, controlled on discharge pressure or reservoir level. Premium efficiency motors; the duty runs thousands of hours a year.
Watch-outs: Surge on power failure is the dominant risk — perform a transient analysis and provide surge vessels, air valves or a controlled-closure check valve. Suction pipework geometry: an elbow immediately upstream of a double-suction pump that bends in a plane parallel to the shaft (a horizontal elbow on a horizontal pump) will unbalance the two eyes and cause vibration and noise. Minimum flow during low demand hours.

P-03 Filter backwash 200–2 000 L/s · 6–15 m

Liquid: Treated water, short intermittent duty at very high flow and low head.
Pump type: Mixed flow or large end-suction; frequently a vertical mixed-flow pump in a clearwell. An elevated backwash tank with a modest fill pump is often cheaper and gentler than a large backwash pump.
Impeller: Mixed flow, n_q 80–150. This duty sits well outside the radial impeller range.
Materials: Cast iron with bronze or stainless impeller, NSF/ANSI 61 compliant.
Sealing: Single mechanical seal; consider flush arrangements that tolerate long idle periods without drying out.
Drive & control: Soft start or VFD with a controlled ramp, so backwash rate of rise does not lift media into the troughs. Rate control by flow with a modulating valve or by speed.
Watch-outs: Air release at start-up after idle periods. Media loss from a rate step change. Motor sizing must cover the low-resistance case at the start of backwash when the bed is clean and expanded.

P-04 Seawater intake for desalination 100–5 000 L/s · 10–40 m

Liquid: Seawater, roughly 20 000 mg/L chloride, oxygenated, biofouling, with sand and marine growth. Often intermittently chlorinated.
Pump type: Vertical turbine in an open intake sump, or submersible in a beach well. Large split case pumps where an onshore forebay exists.
Impeller: Mixed flow closed bowl.
Materials: Super duplex CD3MWCuN or nickel aluminium bronze C95800 throughout. 316L is not acceptable in aerated seawater — crevice corrosion under gaskets and wear rings starts within months. Column pipe in GRP or coated carbon steel with cathodic protection; avoid mixed couples that set up galvanic cells.
Sealing: Cartridge seal with external flush from filtered water, or packing with clean flush. Hard faces both sides, silicon carbide against silicon carbide.
Drive & control: Variable speed matched to train recovery; motors rated for coastal humidity and salt, minimum IP55 with marine paint specification.
Watch-outs: Galvanic compatibility across every wetted couple. Biofouling of columns and the intake screen. Sand erosion at high tip speed — keep bowl velocities moderate. Shock chlorination compatibility with elastomers; use EPDM, not nitrile.

P-05 Raw sewage lift station, submersible 10–500 L/s · 8–45 m

Liquid: Unscreened municipal sewage: wipes, hair, rag, grit, grease, plastics, sulphide, pH 6–9, occasionally trade effluent.
Pump type: Submersible non-clog on a guide rail, two or more units with duty/standby alternation. Dry-pit submersible for larger influent stations where access matters.
Impeller: Self-cleaning swept-back single vane is the current default. Two-vane closed non-clog where screening is reliable and efficiency is the priority. Chopper where wipes are chronic and the force main is small bore. Minimum free passage 75–100 mm for municipal duty.
Materials: EN-GJL-250 grey iron casing, hardened iron or CF8M impeller, 420 or 431 stainless shaft, 316 fasteners. Choose 316 or duplex where sulphide and low pH have caused casing loss. Epoxy or ceramic-filled coating on the hydraulic extends life in abrasive catchments.
Sealing: Tandem mechanical seals in an oil-filled chamber: silicon carbide against silicon carbide on the wet side, carbon against ceramic or SiC inboard. Moisture probe in the oil chamber and in the stator, wired to the control panel rather than merely fitted.
Drive & control: Level control by ultrasonic or pressure transducer with float backup. VFD where the force main is long or where flow must be smoothed, with a firm minimum speed. Alternate pumps every cycle; fit a daily full-speed flush run and a periodic reverse de-rag routine.
Watch-outs: Wet-well geometry causes more trouble than the pump: provide benching, avoid flat floors and dead corners, and size the working volume for the allowable motor starts per hour (typically 6–15 for direct-on-line, more for soft start). Keep force main velocity at or above roughly 0.75 m/s at least once a day to scour grit. Grease cap and rag mat formation. Hydrogen sulphide attack on the concrete and on the electrical enclosure. Confirm minimum submergence over the volute for motor cooling.

P-06 Storm and combined sewer overflow pumping 100–10 000 L/s · 2–15 m

Liquid: Dilute sewage and stormwater with heavy grit, gravel, road debris and occasional large objects. Runs rarely, then hard.
Pump type: Vertical mixed flow or axial flow column pumps for large low-lift stations; submersible non-clog for smaller ones. Screw pumps remain competitive at very low lift.
Impeller: Mixed flow or propeller, n_q 100–200.
Materials: Cast iron with hardened or stainless impeller; consider high-chrome iron where grit loading is severe.
Sealing: Simple and robust: packing or heavy-duty single seal; the duty is intermittent and long idle periods are the real stress.
Drive & control: Level-based cascade starting. Soft start to limit inrush on standby generators. Test-run regime is essential for a pump that may not operate for months.
Watch-outs: Axial pumps draw more power as flow falls, so motor protection must be checked at the throttled or high-static case. Air entrainment and vortexing in shallow sumps. Sediment deposition in the sump between events. Gate and flap valve slam.

P-07 Grit slurry and grit classifier feed 5–80 L/s · 5–25 m

Liquid: Sand, silt and gravel in water, 1–10 % solids by weight, highly abrasive with sharp particles.
Pump type: Recessed impeller (torque flow) pump, or a hard-metal horizontal slurry pump. Air-lift for shallow chambers.
Impeller: Fully recessed so solids pass through the casing without striking the vanes, or a heavy slurry impeller running at reduced speed.
Materials: Ni-Hard 4 or 27 % chromium white iron, 600–700 HB, or natural rubber lining where particles are fine and rounded. Hardened wear plates that can be replaced without replacing the casing.
Sealing: Packing with a clean-water lantern ring flush at 0.3–0.7 bar above discharge pressure, or a double mechanical seal with a clean barrier. Never a single seal exposed to the slurry.
Drive & control: Belt drive allowing speed change by pulley, so tip speed can be reduced to trade head for wear life. Keep impeller peripheral speed below roughly 25 m/s.
Watch-outs: Wear rate rises with roughly the cube of velocity — every design decision that raises speed shortens life disproportionately. Keep pipe velocity high enough to prevent settling (about 1.5–2.5 m/s) but no higher. Provide flush connections and a drain at every low point.

P-08 Scum, grease and floatables 2–30 L/s · 5–25 m

Liquid: Fats, oils and grease with water, rag, plastics and air. Congeals below about 25 °C.
Pump type: Chopper pump or recessed impeller; progressive cavity where the scum is thick and cold.
Impeller: Cutter or fully recessed; the ability to handle entrained air matters as much as solids.
Materials: Cast iron with hardened cutting elements; 316 where washdown chemicals are used.
Sealing: Double mechanical seal with barrier fluid; grease will foul a single seal face quickly.
Drive & control: Timed operation tied to the scum trough or skimmer; short runs at full speed.
Watch-outs: Heat trace and insulate scum lines; provide steam or hot-water flush connections. Air binding on a centrifugal pump handling a floating layer — flooded suction is close to mandatory. Slope lines continuously and avoid long horizontal runs.

P-09 Primary sludge withdrawal 2–40 L/s · 5–30 m

Liquid: 2–6 % total solids, with grit, rag and grease. Strongly non-Newtonian above about 3 %.
Pump type: Progressive cavity or rotary lobe is the mainstream choice. Chopper centrifugal is viable for thin primary sludge on short pipe runs with generous head margin.
Impeller: If centrifugal: chopper or recessed, with the head derated for sludge friction (see Section 8).
Materials: Cast iron body with hardened rotor or impeller; 316 where sulphide is high.
Sealing: Double mechanical seal, or packing with flush on PC pumps.
Drive & control: Timed or density-controlled withdrawal. Variable speed to match the blanket, with a low-flow limit that keeps the line scoured.
Watch-outs: Pipe friction in 2–6 % sludge is typically 1.5 to 4.5 times the clean-water value, and more in laminar flow; a centrifugal pump sized on water curves will simply stop delivering as solids rise. Provide a water flush and a rodding point on every sludge line. Dry running destroys PC stators in minutes — fit protection.

P-10 Return activated sludge (RAS) 30–1 500 L/s · 1.5–8 m

Liquid: Settled biological sludge, 0.4–1.2 % solids, flocculent and shear-sensitive, with some rag carried over from the primary stage.
Pump type: Submersible mixed-flow or non-clog in a RAS pit; vertical or horizontal mixed flow in a dry well; screw centrifugal where floc preservation is a priority. Archimedes screw pumps are still an excellent low-head answer where the geometry allows.
Impeller: Mixed flow, n_q 70–140. A radial end-suction impeller on this duty will be badly oversized in head and permanently throttled.
Materials: Cast iron casing, CF8M or hardened iron impeller, 316 fasteners. Nothing exotic is needed; the liquid is benign.
Sealing: Tandem seals in oil for submersibles; single or double cartridge seal with SiC faces for dry-mounted units.
Drive & control: Variable speed paced to influent flow at a set ratio, or controlled on sludge blanket level. This is one of the highest-value VFD applications in the plant because the duty is friction-light and runs continuously.
Watch-outs: Over-pumping RAS is a classic error: it hydraulically overloads the clarifier, thins the return, and wastes energy. Shear from an oversized high-speed pump degrades settleability. Confirm measurement accuracy — RAS ratio control is only as good as the flow meter on a solids-bearing line. Air entrainment from a shallow RAS pit.

P-11 Nitrate recycle / internal mixed-liquor recirculation 100–3 000 L/s · 0.3–2 m

Liquid: Aerated mixed liquor, 2–5 g/L MLSS, carrying dissolved oxygen that must not reach the anoxic zone.
Pump type: Submersible axial flow propeller pump in a draft tube, or a low-lift mixed flow column pump. In-channel recirculators with slow, large-diameter propellers are common in oxidation ditches.
Impeller: Axial propeller, n_q above 160. Head is typically under one metre; the entire duty is velocity, not pressure.
Materials: Cast iron housing, 316 propeller and shaft. Stainless is justified because the blades are thin and long-lived only if they stay smooth.
Sealing: Standard submersible tandem seal arrangement.
Drive & control: Variable speed set by recycle ratio or by anoxic-zone nitrate measurement. Ratio typically 200–400 % of influent; higher ratios give diminishing denitrification returns and carry more oxygen.
Watch-outs: Never specify a radial pump here. A centrifugal pump forced onto this duty will produce far more head than the channel needs, waste most of the energy across a valve, and shear the biomass. Minimise dissolved oxygen carryover by taking suction from a de-aerated zone and avoiding a free fall at the discharge. Check that the propeller motor does not overload if the channel level rises.

P-12 Waste activated sludge (WAS) 1–40 L/s · 5–25 m

Liquid: 0.5–1.2 % solids biological sludge, sent to thickening or digestion.
Pump type: Non-clog centrifugal for thin WAS; progressive cavity where accurate volumetric wasting is required for solids retention time control.
Impeller: Closed two-vane or self-cleaning single vane.
Materials: Cast iron with CF8M impeller.
Sealing: Double or tandem mechanical seal.
Drive & control: Timed or flow-paced wasting with totalising flow measurement. Continuous small-flow wasting stabilises the process better than large intermittent batches.
Watch-outs: Wasting accuracy directly controls sludge age; a pump that cannot deliver a repeatable low flow undermines process control. Very low flows push a centrifugal pump far left of BEP — consider a smaller pump running longer rather than a large one running briefly.

P-13 Jet aeration and motive-liquid pumping 20–400 L/s · 10–30 m

Liquid: Mixed liquor pumped as motive fluid through jet nozzles where it entrains process air.
Pump type: Non-clog centrifugal, usually dry-mounted, feeding a nozzle manifold. A genuinely friction-dominated duty.
Impeller: Closed two-vane non-clog with a free passage smaller than the nozzle throat, so anything that gets through the pump also gets through the jet.
Materials: Cast iron casing, stainless impeller; nozzles and mixing tubes in 316 or in a wear-resistant polymer.
Sealing: Double mechanical seal with barrier fluid.
Drive & control: Usually fixed speed with the air side modulated; the motive flow sets the mixing energy and should not be reduced below the manufacturer's floor.
Watch-outs: Nozzle blockage changes the system curve abruptly and pushes the pump left. Provide isolation and rodding access to the manifold. Solids passage through the pump must be smaller than the nozzle, not larger, or the jets block instead of the pump.

P-14 Moving bed and fixed film recirculation 20–600 L/s · 2–12 m

Liquid: Process water with sloughed biofilm; in an MBBR, carriers must remain in the reactor and out of the pump.
Pump type: Non-clog or mixed flow; trickling filter recirculation commonly uses submersible non-clog units.
Impeller: Non-clog closed or self-cleaning; sized to pass sloughed film without roping.
Materials: Cast iron and stainless; nothing unusual.
Sealing: Standard tandem submersible seal.
Drive & control: Variable speed on recirculation ratio, which in trickling filters is used to keep wetting rate up at low flow.
Watch-outs: Carrier retention screens must be intact; plastic carriers entering a pump jam it and are expensive to lose. Sloughing events produce a sudden solids spike — size for that, not for the average.

P-15 Anaerobic digester recirculation and heating loop 10–150 L/s · 8–30 m

Liquid: Digesting sludge, 2.5–8 % TS at 35–40 °C (mesophilic) or 50–57 °C (thermophilic). Contains grit, rag, struvite crystals, entrained biogas and hydrogen sulphide. Strongly non-Newtonian.
Pump type: Chopper centrifugal is the common choice for recirculation through an external heat exchanger; progressive cavity or rotary lobe where solids are above about 5 % or the loop is long. Screw centrifugal where the heat exchanger tolerates lower head.
Impeller: Chopper with hardened cutter bar, or recessed. Passage must clear rag that has survived the whole plant.
Materials: Ductile or cast iron casing with hardened iron or 316 wetted parts; hardened chopping elements. 316L is adequate for the liquid but wear, not corrosion, sets the life.
Sealing: API 682 dual pressurised seal with a barrier fluid system (Plan 53B) is the reliable arrangement, with SiC against SiC faces. A quench (Plan 62) helps where struvite crystallises on the atmospheric side. The seal must not depend on the sludge for lubrication.
Drive & control: Continuous or timed recirculation with temperature control on the heat exchanger. Motors and all electrical equipment must suit the hazardous area classification — typically Zone 1 or 2 under ATEX, or Class I Division 1 or 2 under the NEC. Dry-run and low-flow protection are mandatory.
Watch-outs: Entrained biogas is the biggest operational problem: even 5–10 % gas by volume will make a centrifugal pump lose prime and vapour-lock. Provide a flooded suction, a short straight suction line, and a high-point vent back to the digester. Struvite scales rapidly in pipework and on seal faces after any pressure drop. Grit accumulates at the digester floor and finds the suction. Thermal expansion and heat exchanger fouling change the system curve over a run.

P-16 UASB, EGSB and IC reactor feed 10–500 L/s · 6–25 m

Liquid: Acidified industrial wastewater: brewery, distillery, dairy, pulp, food processing. pH 4–7, volatile fatty acids, chloride from cleaning chemicals, sometimes 35–40 °C, often with fibre and fat.
Pump type: End-suction or self-priming centrifugal for feed from the conditioning tank; frequency-controlled to hold a steady organic loading rate.
Impeller: Closed or semi-open depending on fibre. Fat and fibre from food industry effluent will rope a standard closed impeller.
Materials: 316L as a minimum because of acidity and chloride from clean-in-place chemicals; duplex 2205 where chloride exceeds about 1 000 mg/L (less in warm effluent) or pH falls below 4. Lined or all-plastic pumps for chemically severe streams. Carbon steel and cast iron corrode quickly in acidified effluent.
Sealing: Single cartridge seal with a flush plan suited to the fluid; a quench prevents the seal gumming with fat. Double seal where the effluent contains abrasives.
Drive & control: Variable speed on flow, paced by the buffer tank level and by organic loading. Feed must be smooth — slugging an anaerobic reactor destabilises it.
Watch-outs: Corrosion is the main risk on the feed side, unlike municipal digesters. Sulphide generation in the buffer tank attacks copper and iron. Temperature control matters: cold feed shocks the biomass. Check that the pump does not aerate the feed — introduced oxygen inhibits methanogens.

P-17 Granular sludge recirculation and upflow velocity control 50–2 000 L/s · 2–12 m

Liquid: Reactor effluent recirculated to set upflow velocity, carrying anaerobic granules 0.5–3 mm across that must survive the journey.
Pump type: Screw centrifugal or low-speed open-impeller centrifugal. Axial flow where the lift is very small. The design intent is the opposite of a normal pump specification: the lowest shear that will do the job.
Impeller: Screw centrifugal single helical vane, or a wide open impeller at reduced speed. Run at 700–1 000 rpm rather than 1 450 where the hydraulic allows.
Materials: 316L or duplex depending on chloride and pH; the same corrosion logic as the feed pump applies.
Sealing: Single cartridge seal with flush; biogas in the recirculated liquid argues for a double seal where the pump can run partially gas-bound.
Drive & control: Variable speed to hold the design upflow velocity — roughly 0.5–1.5 m/h in a UASB, 6–12 m/h in an EGSB, and higher again in the riser of an IC reactor. Recirculation is therefore a process variable, not a fixed rate.
Watch-outs: Granule attrition is cumulative and silent; it shows up months later as rising effluent solids and falling reactor capacity. Avoid throttling valves in the recirculation line, which shear more than the pump does. Biogas entrainment causes flow instability. Calcium carbonate and struvite scaling on impellers in hard, phosphate-rich effluents.

P-18 Digestate transfer and post-digestion storage 5–80 L/s · 10–40 m

Liquid: Digested sludge, 2–6 % TS, high ammonia, high alkalinity, struvite-forming, warm.
Pump type: Progressive cavity or rotary lobe for thick digestate; chopper centrifugal for thin digestate over short distances.
Impeller: Chopper or recessed if centrifugal.
Materials: Cast iron with hardened or 316 wetted parts. Ammonia rules out copper alloys and brass fittings entirely.
Sealing: Double seal with barrier fluid and a quench to keep struvite off the atmospheric face.
Drive & control: Variable speed with flow measurement; batch transfers on level.
Watch-outs: Struvite (magnesium ammonium phosphate) precipitates wherever pressure drops or turbulence increases — at valves, elbows, seal faces and pump discharge. Design for chemical cleaning access, or dose to control it. Hazardous area classification may still apply near the digester.

P-19 Biogas condensate and foul condensate 0.1–3 L/s · 5–25 m

Liquid: Water condensed from biogas: saturated with hydrogen sulphide and carbon dioxide, pH often 4–6, aggressive to steel and copper.
Pump type: Small self-priming or submersible sump pump, or a sealless magnetic drive unit.
Impeller: Closed, small.
Materials: 316L at minimum; thermoplastic (PP, PVDF) or lined pumps are a better answer. No cast iron, no bronze, no copper anywhere in the circuit.
Sealing: Sealless is ideal; otherwise a double seal, since leakage releases hydrogen sulphide into an occupied space.
Drive & control: Level-controlled, with hazardous-area-rated electrics where the sump is connected to the gas system.
Watch-outs: This tiny duty causes outsized trouble: a corroded condensate pump lets liquid back up into gas lines and trips the whole digestion plant. Specify the material properly and provide a duty/standby pair.

P-20 MBR membrane tank recirculation 100–3 000 L/s · 1–5 m

Liquid: Mixed liquor at 8–12 g/L MLSS, distinctly viscous and shear-thinning, recirculated at three to five times permeate flow to control solids concentration in the membrane tank.
Pump type: Submersible axial or mixed flow propeller pump in a draft tube is the correct machine. Non-clog centrifugal only where the geometry forces a real lift.
Impeller: Axial or mixed flow, n_q above 130. The duty is almost pure friction and velocity head.
Materials: Cast iron casing with 316 propeller and shaft.
Sealing: Tandem submersible seals with moisture detection.
Drive & control: Variable speed tied to permeate flux so the recirculation ratio stays constant across the day. Reducing recirculation at low flux saves substantial energy.
Watch-outs: Apply a viscosity correction. At 10 g/L MLSS the effective friction factor and the pump's absorbed power are materially higher than the clean-water values, and head output falls — see Section 8. Fine screening to 1–3 mm upstream of an MBR is not optional; hair and fibre that reach the membranes cannot be removed by cleaning. Excess shear reduces floc size and accelerates fouling, so do not specify more recirculation head than the hydraulic profile requires.

P-21 MBR permeate extraction and backpulse 5–200 L/s · −5 to +15 m

Liquid: Filtered permeate, clean, but drawn under vacuum from a submerged membrane at −0.1 to −0.5 bar transmembrane pressure. Air is routinely entrained.
Pump type: Self-priming centrifugal, or a rotary lobe pump where reversal for backpulse is required from the same machine. Some designs use a gravity siphon with a level difference and no pump at all.
Impeller: Closed, designed for suction service with air handling capability.
Materials: 316L wetted parts, because the same pump is exposed to hypochlorite and citric acid during maintenance cleans. EPDM elastomers for hypochlorite compatibility.
Sealing: Mechanical seal rated for vacuum service — a seal that relies on internal pressure to close will leak air inward under suction. Specify a balanced cartridge seal suitable for negative pressure.
Drive & control: Variable speed on flux or level, with transmembrane pressure monitored continuously as the fouling indicator. Reversal or a separate backpulse pump on a timed cycle, typically every 8–15 minutes.
Watch-outs: The suction runs under vacuum (−0.1 to −0.5 bar g), so NPSH available is small. It must still exceed NPSH required with margin, so select the pump explicitly for suction-lift service; a standard end-suction pump will cavitate. Air ingress through flanges and seals corrupts flux measurement and can air-bind the pump. Never allow the pump to pull more vacuum than the membrane manufacturer permits — fit a vacuum limit interlock, because excessive transmembrane pressure damages the module irreversibly.

P-22 Ultrafiltration and microfiltration feed 20–500 L/s · 15–60 m

Liquid: Pre-screened surface water, secondary effluent or seawater at 1–4 bar feed pressure.
Pump type: End-suction or horizontal split case; vertical multistage for small skids.
Impeller: Closed multi-vane.
Materials: 316L for fresh water; duplex or super duplex for seawater pretreatment. The pump also sees clean-in-place chemicals, so check acid and hypochlorite compatibility of elastomers and coatings.
Sealing: Single cartridge seal, Plan 11, with faces suited to intermittent chemical exposure.
Drive & control: Variable speed on flux or feed pressure. The system curve rises through a filtration run as the membranes foul, then resets at backwash — size across that range.
Watch-outs: Pressure spikes during valve sequencing can exceed module ratings; use slow-acting valves and a controlled ramp. Do not let the pump run against a closed system during backwash sequencing. Strainer differential monitoring upstream.

P-23 Brackish water RO high-pressure feed 10–300 L/s · 100–300 m (10–30 bar)

Liquid: Cartridge-filtered brackish water, 1 000–10 000 mg/L TDS, dosed with antiscalant and often acid.
Pump type: Horizontal ring-section (BB4) or axially split (BB3) multistage or vertical multistage. Single-stage high-speed pumps for smaller trains.
Impeller: Closed radial, low n_q, several stages in series.
Materials: 316L up to about 1 000 mg/L chloride at ambient temperature, with some margin for the tight crevices of a high-pressure pump; duplex 2205 above that and wherever acid dosing lowers pH; super duplex as chloride approaches seawater. Check the chloride and temperature combination against the pitting guidance in Section 9.
Sealing: Balanced cartridge seal rated for the full discharge pressure at the stuffing box, with a Plan 11 or Plan 13 flush. Seal face selection must tolerate high pressure and the occasional low-conductivity permeate flush.
Drive & control: Variable speed for recovery control and soft start. Interlock on low suction pressure from the cartridge filters, and on high discharge pressure.
Watch-outs: Never start against a closed discharge or allow dry running; a multistage pump self-destructs quickly. NPSH available is often marginal after the cartridge filters as they load — base the calculation on the dirty filter condition. Axial thrust rises with differential pressure; confirm the balance device and thrust bearing at maximum duty. Rapid valve closure in a high-pressure loop causes damaging transients.

P-24 Seawater RO high-pressure feed 20–600 L/s · 550–750 m (55–75 bar)

Liquid: Pretreated seawater, roughly 20 000 mg/L chloride, at 55–75 bar.
Pump type: Barrel-casing multistage (API 610 type BB5) or axially split multistage for large trains. Axial piston positive displacement pumps for small trains below roughly 50 m³/h.
Impeller: Closed radial, 5–12 stages, with balance drum or opposed impellers for thrust.
Materials: Super duplex CD3MWCuN (PREN above 40) is the standard. 6 % molybdenum austenitic alloys and nickel aluminium bronze are alternatives. 316L is not acceptable at these chloride levels and pressures.
Sealing: API 682 cartridge seal rated for high pressure, often dual with a barrier, faces in silicon carbide. Consider a low-pressure stuffing box arrangement where the design permits.
Drive & control: Variable speed or a fixed-speed pump with a booster on the energy recovery circuit. Isobaric pressure exchangers recover roughly 95 % of the concentrate energy and need a matched low-differential, high-flow booster pump, itself in super duplex.
Watch-outs: Energy recovery integration dominates the design; specific energy for seawater RO falls from about 6 kWh/m³ without recovery to 2.5–3.5 kWh/m³ with a modern isobaric device. Crevice corrosion at gaskets and under deposits is the failure mode, not general corrosion. Hydraulic transients on trip are severe at 70 bar. Cartridge filter condition governs NPSH and wear.

P-25 Clean-in-place and chemical cleaning circuits 5–150 L/s · 15–50 m

Liquid: Sodium hypochlorite at 200–1 000 mg/L, citric or oxalic acid, caustic soda, sometimes warmed to 35–40 °C. Alternating alkaline and acid duty.
Pump type: End-suction centrifugal in plastic or lined construction, or a sealless magnetic drive pump.
Impeller: Closed, in the same material as the casing.
Materials: PVDF or PP for the wetted path, or 316L tolerates intermittent dilute cleaning solutions (hypochlorite up to about 1 000 mg/L) at ambient temperature with thorough rinsing afterwards, but never 10–15 % hypochlorite product. Titanium where hypochlorite concentration is high. Elastomers in EPDM — nitrile fails quickly in hypochlorite and FKM is attacked by hot caustic.
Sealing: Sealless is preferable for an intermittent chemical duty that sits idle between cleans, because a dried seal face leaks on the next start. Otherwise a double seal with a compatible barrier.
Drive & control: Fixed or variable speed with temperature and flow interlocks. Crossflow velocity during cleaning is specified by the membrane supplier.
Watch-outs: Mixed-chemical service is the hard part — a material that is excellent for acid may fail in hypochlorite. Specify for the worst of the cleaning chemicals. Sealless pumps must never run dry, so interlock against an empty CIP tank.

P-26 Thickened sludge to dewatering 1–25 L/s · 10–60 m

Liquid: 4–12 % TS. Apparent viscosity in the hundreds to thousands of centipoise; yield stress rises steeply with solids.
Pump type: Progressive cavity or rotary lobe. Centrifugal chopper or recessed pumps stop being practical above about 4–5 % TS even on short lines, and above about 3 % on long ones.
Impeller: Not applicable — rotor and stator, or lobes.
Materials: Hardened rotor with nitrile or EPDM stator; hardened lobes. Grit is the wear driver.
Sealing: Packing with flush, or a cartridge mechanical seal with a clean quench.
Drive & control: Variable speed feeding the dewatering device, with polymer dosing paced to the same signal.
Watch-outs: Do not shear conditioned sludge after polymer addition. Provide a pressure relief device: a positive displacement pump against a blocked line will fail something. Dry running destroys stators. Include water flush and rodding points.

P-27 Centrate, filtrate and sidestream return 2–60 L/s · 5–30 m

Liquid: Liquid returned from dewatering: high ammonia, high phosphate, warm, struvite-forming, with fine solids.
Pump type: Non-clog centrifugal or submersible.
Impeller: Closed two-vane or self-cleaning; passages that resist scaling.
Materials: Cast iron with 316 impeller; no copper alloys because of ammonia.
Sealing: Double seal with a quench to suppress crystallisation on the atmospheric face.
Drive & control: Level or flow controlled; equalise the return so it does not shock the biological stage during dewatering hours.
Watch-outs: Struvite deposits build in pipes and on impellers within weeks in some plants. Plan for acid cleaning access, or treat the sidestream. Returning a concentrated ammonia load to the head of works at a single time of day can destabilise nitrification.

P-28 Sludge blending and transfer between tanks 5–60 L/s · 8–35 m

Liquid: Mixed primary and secondary sludge, 2–5 % TS, variable hour to hour.
Pump type: Chopper centrifugal for thin blends and short runs; progressive cavity where solids or distance increase.
Impeller: Chopper or recessed.
Materials: Cast iron with hardened wetted parts.
Sealing: Double mechanical seal with barrier.
Drive & control: Variable speed with density measurement where blend ratio matters.
Watch-outs: Solids content varies far more than designers assume; select on the thickest credible case and check the thinnest for runout. Line velocity must stay above about 1.0 m/s to avoid deposition.

P-29 Leachate and landfill gas condensate 1–50 L/s · 15–120 m

Liquid: Aggressive: chloride often 2 000–10 000 mg/L, ammonia several thousand mg/L, variable pH, high hardness, dissolved iron and manganese, heavy scaling tendency.
Pump type: Submersible borehole pump in the leachate well, or horizontal end-suction at the treatment plant.
Impeller: Closed, with generous clearance to tolerate scale.
Materials: Duplex 2205 as a floor at these chloride levels, super duplex at the upper end; 904L and alloy 20 where the liquid is also acidic. Non-metallic (PP, PVDF) for small duties.
Sealing: Double seal with barrier fluid; scaling will kill a single seal.
Drive & control: Level control with anti-dry-run protection; hazardous area rating where landfill gas is present.
Watch-outs: Iron and calcium scaling blocks impellers and instrumentation. Plan acid cleaning. Corrosion allowances on fasteners and lifting chains are routinely forgotten and are the first things to fail.

P-30 Sodium hypochlorite transfer and dosing 0.05–10 L/s · 10–40 m

Liquid: 10–15 % sodium hypochlorite. Decomposes and releases oxygen gas, especially when warm, which vapour-locks pumps and blocks dosing lines.
Pump type: Diaphragm metering pump for dosing; sealless magnetic drive centrifugal in thermoplastic for transfer. Peristaltic for small, gassy duties.
Impeller: Closed, in PVDF or PTFE-lined construction.
Materials: PVDF, PTFE, CPVC or titanium. Stainless steels pit rapidly in hypochlorite and must not be used. No bronze, no cast iron, no Monel. Gaskets and diaphragms in PTFE, FKM or peroxide-cured EPDM — not nitrile.
Sealing: Sealless is strongly preferred; a leaking hypochlorite seal is both a corrosion and a safety problem.
Drive & control: Flow-paced dosing with residual trim control. Provide calibration column and degassing valve.
Watch-outs: Gas binding is the dominant failure. Provide a flooded suction, rising suction line without high points, a degassing dosing head, and keep the storage cool and out of sunlight. Hypochlorite strength decays with temperature and time, which changes the required dose rate seasonally.

P-31 Ferric chloride, alum and coagulant dosing 0.02–5 L/s · 10–40 m

Liquid: Ferric chloride at roughly 40 %: extremely corrosive, acidic, staining, and can crystallise in cold weather, at temperatures that depend on its strength. Alum and PAC are acidic but less aggressive.
Pump type: Diaphragm metering pump, or magnetic drive centrifugal in lined or plastic construction.
Impeller: Closed, PVDF or PTFE-lined.
Materials: PVDF, CPVC, PTFE-lined, FRP with vinyl ester, rubber-lined, or titanium. 316 stainless steel fails in ferric chloride — it is a classic pitting and crevice corrosion test reagent. Hastelloy C-276 and titanium are the metallic options.
Sealing: Sealless magnetic drive, or double seal with compatible barrier.
Drive & control: Flow-paced with a stroke or speed adjustment; dilution water at the injection point to prevent local precipitation.
Watch-outs: Heat trace and insulate outdoor lines against crystallisation. Provide secondary containment and eyewash. Ferric stains everything permanently; plan for spill management. Dosing lines block at the injection quill — use a removable quill with isolation.

P-32 Lime slurry and powdered activated carbon 0.1–10 L/s · 10–40 m

Liquid: 5–30 % lime slurry: abrasive, settles rapidly, and scales every surface it touches. PAC is abrasive and dusty.
Pump type: Peristaltic hose pump for dosing, progressive cavity for transfer, or a rubber-lined horizontal slurry pump for large flows.
Impeller: If centrifugal: rubber-lined or high-chrome, at low speed.
Materials: Natural rubber lining, high-chrome iron, or hose in EPDM. Steel scales and then abrades.
Sealing: Peristaltic avoids the question entirely, which is why it dominates this duty. Otherwise packing with generous clean flush.
Drive & control: Continuous recirculation loop past the injection point so the slurry never sits still; dose by pinch valve or by pump speed.
Watch-outs: Never run a lime line dead-ended. Provide flush connections and unions for rodding at every bend. Keep velocity above 1.2 m/s to hold solids in suspension. Scale removal needs acid cleaning access.

P-33 Polymer preparation and dosing 0.02–3 L/s · 10–50 m

Liquid: Neat emulsion or dissolved polymer solution, 0.1–0.5 %, viscous and shear-sensitive.
Pump type: Progressive cavity for solution transfer, diaphragm or gear pump for neat emulsion dosing into the make-up unit.
Impeller: Not applicable — centrifugal pumps shear the polymer chain and destroy its flocculating power.
Materials: 316 or plastic; the chemistry is benign, the mechanics are not.
Sealing: Packing or single seal; polymer is slippery and undemanding on seals but will gum on an exposed face.
Drive & control: Variable speed paced to the sludge feed rate, with ageing time provided in the make-up system.
Watch-outs: Shear anywhere in the path — pump, valve, long turbulent line — degrades performance and raises chemical cost. Keep velocities low and dose as close to the mixing point as possible.

P-34 Sulphuric acid and caustic soda 0.02–5 L/s · 10–40 m

Liquid: 93–98 % sulphuric acid, or 25–50 % sodium hydroxide. Both are hazardous; caustic crystallises at low temperature at 50 % concentration.
Pump type: Sealless magnetic drive or canned motor pump; diaphragm metering for dosing.
Impeller: Closed, in alloy or fluoropolymer.
Materials: Concentrated sulphuric acid: alloy 20 (CN7M) or PTFE-lined; note that carbon steel is used for storage of concentrated acid but fails at dilute concentrations, so never mix the two contexts. Caustic: carbon steel or 316 at moderate temperature, nickel alloys when hot. Elastomers in PTFE or EPDM for caustic; PTFE, FFKM or FKM for concentrated sulphuric acid, never EPDM or nitrile.
Sealing: Sealless is the default for safety reasons.
Drive & control: Flow-paced with pH trim; low-level interlock to prevent dry running of a sealless pump.
Watch-outs: Dilution of concentrated acid changes the material requirement completely. Heat trace 50 % caustic lines above 15 °C. Provide containment, deluge and emergency isolation at the pump.

P-35 Final effluent, reuse and UV feed 20–2 000 L/s · 5–60 m

Liquid: Treated effluent, low solids but not clean; biofilm forms readily.
Pump type: End-suction or split case; submersible in an effluent wet well.
Impeller: Closed multi-vane.
Materials: Cast iron with 316 impeller; full 316 where the effluent is chlorinated or reused.
Sealing: Single cartridge seal, Plan 11.
Drive & control: Variable speed on downstream demand or level; UV systems need a stable flow for dose validation.
Watch-outs: Flow stability matters more here than efficiency, because UV dose depends on it. Biofilm on instruments and in wet wells.

P-36 Plant service water and seal water 2–50 L/s · 40–90 m

Liquid: Final effluent or potable water used for washdown, screen sprays, polymer make-up, seal flush and chemical dilution.
Pump type: Vertical or horizontal multistage with a pressure vessel and automatic self-cleaning strainer.
Impeller: Closed multi-vane, several stages.
Materials: 316 throughout where effluent is the source; the duty is continuous and the liquid is not clean.
Sealing: Single cartridge seal with its own clean supply where the service water itself is dirty.
Drive & control: Pressure-controlled variable speed with a small accumulator to avoid short cycling.
Watch-outs: This is the most commonly undersized system on a plant. Add up every seal flush, spray bar and dilution demand, including simultaneous peaks. Poor service water quality causes seal failures across the whole site, so specify the strainer properly. Cross-connection control between effluent service water and potable water is a regulatory requirement, not an option.

P-37 Drainage, dewatering and sump pumping 1–50 L/s · 5–30 m

Liquid: Building and gallery drainage: spillage, washdown, grit, rag, whatever falls in.
Pump type: Small submersible with a vortex impeller, portable or fixed.
Impeller: Recessed or semi-open — reliability beats efficiency for a pump that runs a few minutes a day.
Materials: Cast iron or 316 where the drainage carries chemicals.
Sealing: Standard submersible tandem seal.
Drive & control: Float or conductivity level switches, with a high-level alarm to the control system.
Watch-outs: Sump pumps sit idle for weeks and then must start on demand. Seals dry out, floats foul, and non-return valves seize. Include them in the planned maintenance routine and test them. Chemical spillage may reach a sump never designed for it — check drainage routing against the chemical inventory.

P-38 Fire water 30–300 L/s · 70–120 m

Liquid: Stored water, stagnant between tests.
Pump type: Listed and approved fire pump set: horizontal split case or vertical turbine, with a jockey pump, in accordance with NFPA 20 or the local equivalent.
Impeller: Closed, with a curve shape mandated by the standard — shutoff head no more than 140 % of rated, and at least 65 % of rated head at 150 % of rated flow.
Materials: As listed by the approval body; bronze-fitted cast iron is typical.
Sealing: Packing, deliberately — a controlled drip is expected and easily verified.
Drive & control: Electric or diesel drive with a dedicated controller, automatic start on pressure drop, manual stop. Never on a variable speed drive unless specifically listed.
Watch-outs: This duty is governed by the approval standard, not by ordinary selection practice. Routine churn testing (weekly for diesel drivers, monthly for many electric drives under NFPA 25) and annual flow testing are part of the specification. Do not apply general pump engineering judgement over the listing requirements.

Flow and head bands are typical municipal ranges for orientation; confirm against the specific project hydraulic profile, local code and the manufacturer's certified curves.

Section 8

Sludge and mixed liquor: why clean-water curves mislead

Water is Newtonian. Sludge and concentrated mixed liquor are not: their apparent viscosity falls as shear rate rises, and they have a yield stress that must be exceeded before they move at all. Two separate corrections are needed, and they are often confused.

Correction one: pipe friction

This is the large effect. At the same velocity, head loss in sludge can be several times the clean-water value, and it grows steeply above about 3 % total solids. A centrifugal pump selected on a clean-water system curve will deliver far less flow than intended, or none at all, once solids concentration rises.

Correction two: pump performance

This is usually the small effect for treatment duties. The Hydraulic Institute viscosity correction method (HI 9.6.7) reduces head, flow and efficiency, but the corrections only become significant above roughly 20 mm²/s kinematic viscosity. MBR mixed liquor at 10 g/L behaves as perhaps 2–4 times water viscosity at pumping shear rates, so the pump curve itself barely moves — but absorbed power rises with density and the pipe friction correction above may have raised system friction by 20–40 %. Thick sludge above about 4 % is a different matter, and is the reason the answer there is positive displacement.

Sludge and MLSS correction estimator

Liquid

Concentration % TS

Pipe velocity m/s

Clean-water friction head m

Static head m

Friction multiplier–

Corrected friction head–

Corrected total head–

Specific gravity estimate–

Power relative to water–

–

Indicative design multipliers applied to clean-water friction loss at around 1 m/s. Published data scatter widely with sludge origin, temperature and shear history — measure rheology for any large or critical sludge line.
Total solids	Behaviour	Friction multiplier	Practical pumping choice
< 1 %	Essentially Newtonian	1.0–1.2	Centrifugal, no correction needed
1–2 %	Slightly pseudoplastic	1.2–1.5	Centrifugal non-clog, add head margin
2–4 %	Pseudoplastic with measurable yield stress	1.5–2.5	Chopper or recessed centrifugal on short runs; PD preferred for long runs
4–6 %	Strongly non-Newtonian, plug flow in pipes	2.5–4.5	Progressive cavity or rotary lobe
6–10 %	Yield stress dominates; laminar plug with a thin annulus	4.5–9	Progressive cavity, with generous pressure rating
> 10 %	Paste; moves only under sustained pressure	> 9	High-pressure piston or hydraulic ram pumps, short lines

Two practical consequences. First, keep line velocity at roughly 1.0–1.5 m/s for sludge. Thin sludge becomes turbulent in that range; sludge above about 4 % usually stays laminar, where friction is far worse, and below it solids settle. Second, always include a clean-water flush connection on sludge lines: the ability to push the line clear with water is what keeps a plant running.

Section 9

Materials of construction

Corrosion, abrasion and erosion are three different problems with three different answers. A material chosen for one can be a poor choice for another, and in treatment plants the chosen material is frequently a compromise between them.

Metals

Material	Cast designation	PREN	Strengths	Use in treatment	Limits
Grey cast iron	ASTM A48 Cl.30–35 / EN-GJL-250	–	Cheap, damps vibration, machines well, forgiving casting	Casings for sewage, RAS, stormwater, effluent; most submersible pump bodies	Brittle; graphitic corrosion in soft or acidic water; vulnerable in septic, low-pH or high-chloride sewage
Ductile iron	ASTM A536 65-45-12 / EN-GJS-450-10	–	Twice the tensile strength of grey iron, ductile	Pressure casings on potable high-service and larger sewage pumps	Same corrosion behaviour as grey iron; usually needs an epoxy lining
Bronze	C87600, C87850, C89833 (lead-free); C83600 is leaded and not for potable service	–	Good in clean water, easily cast, non-galling	Impellers and wear rings in potable water pumps	Dezincification of brasses; ammonia causes stress corrosion cracking, so not for digester or centrate service. Check NSF/ANSI 372 lead limits
Nickel aluminium bronze	C95800 / CuAl10Ni5Fe4	–	Excellent seawater resistance, good cavitation resistance	Seawater intake pumps, marine service	Sulphide-polluted stagnant seawater; galvanic couples with stainless
316 / 316L stainless	CF8M / CF3M	24–26	The general-purpose corrosion-resistant workhorse	Impellers, shafts, fasteners, chemical and membrane feed, effluent	Crevice corrosion is rare below about 1 000 mg/L chloride in oxygenated, near-neutral water at ambient temperature (304: about 200 mg/L). Use about 250 mg/L as the cautious figure where tight crevices, deposits or biofilm cannot be avoided, and lower limits when hot. Fails in ferric chloride and hypochlorite. Chloride stress corrosion cracking above about 60 °C
Duplex 2205	CD3MN	34–36	Roughly twice the yield strength of 316 and far better chloride resistance	Brackish RO, leachate, industrial anaerobic feed, aggressive sewage	Not for prolonged service above 300 °C; welding needs ferrite control
Super duplex 2507	CE3MN (cast 2507), CD3MWCuN (Zeron 100 type)	41–45	Seawater-capable, very high strength	Seawater RO high-pressure and booster pumps, seawater intake	Cost; casting and welding require qualified procedures
6 % Mo austenitic	CN3MN (cast AL-6XN), CK3MCuN (cast 254 SMO)	43–47	Seawater-capable, better formability than duplex, non-magnetic	Seawater and high-chloride service where duplex is unsuitable	Cost; lower strength than super duplex
Alloy 20	CN7M	–	Resists sulphuric acid across a wide concentration range	Sulphuric acid transfer and dosing	Poor in strong chlorides and hydrochloric acid
Hastelloy C-276	CW-12MW / CW-6M	>60	Resists oxidising and reducing acids, chlorides, hypochlorite	Ferric chloride, severe chemical duties, hot high-chloride streams	Expensive; usually reserved for small chemical pumps
Titanium Gr. 2	ASTM B367 C-2	–	Outstanding in oxidising chlorides: hypochlorite, ferric chloride, seawater	Hypochlorite and ferric duty, seawater heat exchangers and pumps	Poor in reducing acids without inhibitor; low hardness so poor abrasion resistance; galling
Ni-Hard 4	ASTM A532 Cl.I Type D	–	550–650 HB martensitic white iron	Grit pump casings and impellers	Brittle; no corrosion resistance; cannot be machined conventionally
27 % chromium white iron	ASTM A532 Cl.III Type A	–	600–700 HB with some corrosion resistance	The standard hard-metal slurry pump material for grit and abrasive industrial streams	Brittle; impact from large solids causes chipping

Pitting resistance equivalent and chloride screening

Chromium %

Molybdenum %

Nitrogen %

Service chloride mg/L

Service temperature °C

PREN = Cr + 3.3 Mo + 16 N–

Alloy class–

Indicative chloride ceiling–

–

The ceilings follow the Nickel Institute guidance for oxygenated, near-neutral natural and potable water at ambient temperature (304 about 200 mg/L, 316 about 1 000 mg/L), extended to the higher alloys and halved for every 20 °C above 25 °C. Wastewater with biofilm, deposits or sulphide deserves the cautious end. PREN ranks pitting resistance within the stainless family only. It says nothing about resistance to acids, about crevice geometry, about galvanic effects, or about weld heat-affected zones — all of which decide real service life. Crevices under gaskets, wear rings and deposits are where stainless pumps actually fail.

Non-metallics and linings

Material	Typical limit	Good for	Not for
Polypropylene (PP)	80 °C	Dilute acids and alkalis, hypochlorite at ambient, general chemical transfer	Oxidising acids, solvents, pressure duty, UV exposure without stabiliser
PVDF	120 °C	Hypochlorite, ferric chloride, most acids, high-purity duty	Strong alkalis at high temperature, ketones, amines
PTFE lining / ETFE	150–200 °C	Almost any chemical; the universal lining	Permeation over time; needs a rigid backing shell; poor abrasion resistance
FRP, vinyl ester	90–120 °C	Large chemical casings, ferric and alum service	Mechanical impact, abrasives, high pressure
Natural rubber lining	60–70 °C	Fine rounded abrasives — lime slurry, fine grit	Oils, fats, sharp or large particles, high tip speed
Polyurethane lining	60–70 °C	Fine abrasives with better tear resistance than rubber	Hot water, strong alkalis, hydrolysis in continuous wet service
Ceramic-filled epoxy coating	60–90 °C	Field repair and life extension of cast iron sewage hydraulics; restores clearances	A substitute for correct base material in severe service

Elastomers — the part that is usually specified last and fails first

Elastomer	Range	Good	Fails in	Treatment use
Nitrile (NBR)	−30 to 100 °C	Oils, fats, sewage, abrasion	Hypochlorite, ozone, strong oxidisers, ketones	Sewage pump O-rings, PC stators, oil chambers
EPDM	−40 to 140 °C	Hot water, steam, ozone, hypochlorite, caustic, dilute acids only	Oils, fats, fuels — swells badly	Membrane systems, hypochlorite, CIP circuits, potable water
FKM (fluoroelastomer)	−20 to 200 °C	Oils, fuels, most acids, high temperature	Hot caustic, steam, amines, ketones, low-temperature flexibility	Chemical dosing, digester service, high temperature
FFKM (perfluoroelastomer)	−15 to 300 °C	Essentially universal chemical resistance	Cost only	Critical chemical seals where nothing else survives
PTFE (as a seal element)	−100 to 250 °C	Universal chemical resistance	Not elastic — needs spring energising; cold flow	Bellows seals and chemical pump gaskets

Three material mistakes that recur in treatment plants. Specifying 316 for hypochlorite or ferric chloride service, where it pits within weeks. Using nitrile O-rings in a chlorinated or ozonated circuit, where they harden and crack. And mixing alloys in a seawater or high-chloride circuit — a 316 fastener in a super duplex casing becomes a small anode against a large cathode and dissolves.

Section 10

Shaft sealing

Seal failure is the most frequent cause of centrifugal pump downtime, and in treatment plants it is usually a consequence of the environment the seal was given rather than the seal itself: abrasive product, dry running, crystallising liquid, or a flush that was never commissioned.

Arrangement	How it works	Use when	Accept that
Gland packing	Compressed rings with a controlled leakage rate lubricating the shaft sleeve	Grit and slurry service, fire pumps, large raw water pumps, sites with limited seal skills	It must leak. Budget for flush water, sleeve wear and routine adjustment
Single mechanical seal	One pair of flat faces held together, product-lubricated	Clean liquids: potable water, effluent, membrane feed, chemicals with good lubricity	Any dry running or abrasive ingress destroys it. Product must be clean and must not flash across the faces
Tandem / dual unpressurised	Two seals with a buffer fluid at a pressure below product pressure	Submersible sewage pumps — universally an oil-filled chamber between two seals	The outer seal is a backup, not a barrier. Monitor the chamber for water ingress
Dual pressurised (double)	Barrier fluid held above product pressure, so clean fluid crosses both faces inward	Sludge, digester recirculation, scum, slurry, hazardous chemicals	You now own a barrier fluid system: reservoir, cooling, pressure and level alarms. Commission it, or it is worse than a single seal
Cartridge seal	Pre-assembled and pre-set unit installed as a single component	Almost everywhere — the reliability gain from eliminating field setting errors is large	Higher unit cost, offset several times over by avoided failures
Split seal	Seal that installs without dismantling the pump or removing couplings	Large vertical pumps and awkward installations where teardown is expensive	Pressure and speed limits; higher cost
Sealless (mag drive, canned)	No dynamic seal at all; torque crosses a containment shell	Hazardous chemicals, hypochlorite, acids, anywhere leakage is unacceptable	Zero tolerance for dry running or solids; internal bearings are product-lubricated. Eddy current losses reduce efficiency

Flush plans worth knowing (API 682 numbering)

Plan	Arrangement	Typical treatment use
02	Dead-ended seal chamber, no circulation	Cool clean liquids only; common on small water pumps
11	Recirculation from discharge through an orifice into the seal chamber	The default for clean duties: potable, effluent, membrane feed
13	Recirculation from the seal chamber back to suction	Vertical pumps, and where the seal chamber must be vented upward
21 / 23	Flush through a cooler; 23 circulates a closed loop with a pumping ring	Hot duties — thermophilic digestion, hot industrial effluent. Plan 23 is far more efficient than 21
31	Discharge flush through a cyclone separator, clean fraction to the seal	Moderately dirty water where an external clean supply is unavailable
32	Clean flush injected from an external source	Grit, sludge and slurry pumps. Requires reliable service water at the right pressure
53A / 53B	Pressurised barrier fluid, with nitrogen directly over the reservoir (53A), a bladder accumulator (53B) or a piston accumulator (53C)	Digester recirculation, sludge, hazardous chemical. 53B avoids gas entrainment into the barrier
54	External pressurised barrier circulated by its own system	Multiple pumps served from a central barrier unit, larger plants
62	External quench on the atmospheric side	Crystallising liquids — struvite in digestate and centrate, hypochlorite, caustic. A very cheap fix for a common failure

Face materials

Carbon against silicon carbide: the general-purpose pair for clean water and effluent. Good dry-run tolerance for a few seconds, low friction.
Silicon carbide against silicon carbide: the standard for sewage, sludge and abrasives. Hard, chemically inert, but intolerant of dry running and of thermal shock.
Tungsten carbide against silicon carbide: tougher against impact and edge chipping; cobalt-bound grades are not suitable for aggressive or chloride-bearing liquids, so specify a nickel-bound grade.
Diamond-coated faces: used on severe sludge and digester duties where conventional faces last months; expensive but sometimes the cheapest option per operating hour.

The seal chamber matters as much as the seal. A tapered, large-bore seal chamber lets solids escape centrifugally and lets vapour vent; a traditional narrow stuffing box traps both. When retrofitting a mechanical seal to a pump originally built for packing, changing the chamber is often what actually fixes the reliability problem.

Section 11

Motors, drives and control

The pump is half the machine. Most of the energy, and a fair share of the failures, belong to the motor, the drive and the control logic that decides when the pump runs.

Motor sizing

Non-overloading selection means the motor covers the maximum power the pump can absorb anywhere on its curve at the fitted impeller diameter, not merely at the design duty. For radial pumps that is the runout end; for axial and mixed flow pumps it is the low-flow end, which catches people out.
Typical margins over duty power: 25 % up to 4 kW, 15 % to 40 kW, 10 % above that — unless non-overloading selection already exceeds these.
Do not treat the service factor as design margin. It is a short-term allowance, and running continuously into it shortens insulation life.
Specify efficiency class explicitly: IE3 as a minimum and IE4 where run hours are high, or NEMA Premium equivalents. On a pump running 8 000 hours a year the efficiency difference pays for itself quickly.
Submersible motors need a stated cooling basis. A motor relying on immersion cooling must not be run with the wet well drawn down, and a jacketed motor must have its cooling circuit clear.

Variable speed drives: where they pay and where they do not

The cube law only applies to the friction component. On a system that is mostly static lift, slowing the pump reduces flow a great deal and power much less, and below a certain speed the pump delivers nothing at all while still drawing power.

System	Static share	VFD value	Note
Nitrate recycle, MBR recirculation, RAS	< 20 %	Very high	Near-cubic savings; also the right way to hold a recirculation ratio
Membrane and filter feed	20–50 %	High	Also gives smooth ramping, which protects modules
Distribution and high service	40–70 %	Moderate	Best value is pressure management and reduced leakage, not pump power alone
Sewage lift to a long force main	> 70 %	Low to moderate	Savings are modest; the real benefits are soft starting, flow smoothing and reduced surge. Set a minimum speed that keeps the main scoured
Deep well and borehole	> 85 %	Low	Often better to run fixed speed at BEP and control by tank level

What a VFD requires of the rest of the installation

Inverter-duty insulation to NEMA MG1 Part 31 or IEC 60034-25, particularly with long motor cables where reflected wave voltage doubling occurs.
Shaft grounding rings or insulated non-drive-end bearings to prevent electrical discharge machining of the bearing races — a common early failure on retrofitted drives.
Output filters or dV/dt reactors on cable runs beyond roughly 30–50 m, and screened cable with proper 360-degree glanding.
Harmonic assessment at the point of common coupling; multiple drives on a small supply add up.
Avoidance of resonant speeds — programme skip frequencies once the installed vibration signature is known.
Reduced motor cooling at low speed on self-ventilated motors; check continuous low-speed operation against the motor's derating curve.

Control strategy by duty

Duty	Controlled variable	Strategy
Sewage lift station	Wet well level	Start/stop bands with alternation, or VFD level-trimming with a flush cycle at full speed daily
RAS	Ratio to influent flow, or blanket depth	Flow-paced with a blanket override; avoid chasing the blanket with fast loops
Nitrate recycle	Recycle ratio, or anoxic nitrate	Ratio control with feedback trim from a nitrate analyser
MBR permeate	Flux and transmembrane pressure	Flux setpoint with TMP alarm and relax/backpulse cycles; hard vacuum limit
RO high pressure	Permeate flow and recovery	Speed control with interlocks on suction pressure, conductivity and high discharge pressure
Distribution	Discharge pressure or reservoir level	Lead VFD with lag fixed-speed pumps; pressure setpoint scheduled by time or demand
Digester recirculation	Heat exchanger outlet temperature	Continuous circulation with temperature-modulated heating, not pump cycling
Chemical dosing	Flow-paced with residual trim	Feedforward on flow, feedback on measured residual or pH

Protection to specify, not to assume

Thermal overload and motor winding thermistors; moisture detection in submersible oil chambers and stators; dry-run protection by power monitoring, level or flow for any pump that can lose suction; low-flow protection on multistage and sealless pumps; vibration switches or continuous monitoring on large units; bearing temperature on pumps above roughly 75 kW; and a run-hours-balanced alternation scheme so the standby pump is genuinely proven.

Section 12

Intakes, sumps and pipework

A correctly selected pump will still perform badly if the approach flow is disturbed, the submergence is short, or the suction pipe traps air. These are design errors that cannot be corrected by adjusting the pump.

Suction pipework rules

Suction pipe one or two sizes larger than the flange, with velocity typically 0.9–1.8 m/s.
At least five pipe diameters of straight pipe before the suction flange; ten for a double-suction pump. An elbow near a double-suction pump must lie in a plane perpendicular to the shaft (vertical, for a horizontal pump), never parallel to it, or the two impeller eyes receive unequal flow.
Eccentric reducers with the flat side uppermost on horizontal suction lines, so no air pocket can form.
No high points that can accumulate air; continuous rise toward the pump on a suction lift.
Suction strainers with a free area at least three to four times the pipe area, and a differential pressure indication so a blocked strainer is visible before it starves the pump.

Wet wells and sumps

Design against ANSI/HI 9.8 for submergence, approach velocity, clearances and vortex suppression, and for any large or unusual station, commission a physical or computational model study. Specific points that recur in wastewater:

Benched or trench-type floors so solids are swept toward the intake rather than accumulating in corners. Flat-bottomed wet wells build a sludge bank and a floating grease mat.
Inlet arranged so the incoming flow does not free-fall onto the suction and entrain air. Entrained air of a few percent noticeably degrades performance; ten percent can stop the pump.
Working volume sized on allowable motor starts, balanced against detention time. Too large a wet well means septicity, hydrogen sulphide and odour; too small means excessive starting.
Clearance from the intake bell to the floor and walls per the standard, with a floor cone or splitter where required to break the sub-surface vortex.

Wet well working volume and cycle time

Pump capacity L/s

Permitted starts per hour

Design inflow to check L/s

Wet well plan area m²

Average dry weather inflow L/s

Minimum cycle time–

Required working volume–

Level band–

Cycle at design inflow–

Detention at average flow–

–

Discharge pipework and transients

Check valves: swing check valves slam on reverse flow. For sewage, a ball check or a full-bore swing check with an external lever and weight is normal; nozzle or silent check valves close before flow reversal and are the right answer on high-head clean-water pumps.
Air valves: combination air release and vacuum break valves at every high point on a force main. Sewage duty requires a sewage-pattern air valve, not a water-pattern one, or it will block.
Surge: run a transient analysis for long force mains, high static lifts and any system where pump trip can cause column separation. Mitigation options include surge vessels, one-way surge tanks, air vessels, flywheels, and controlled valve closure. Retrofitting surge protection after a main has burst is the expensive path.
Force main velocity: aim for at least 0.75 m/s at some point each day to scour grit, with a normal operating range of about 1.0–2.4 m/s. Where a VFD keeps the pump slow, programme a periodic full-speed flush.
Baseplate and alignment: grouted baseplate, laser alignment after piping is connected, and flange loads within the pump's allowable nozzle load. Pipe strain distorts the casing, closes clearances and shortens seal and bearing life.
Vibration acceptance: reference ANSI/HI 9.6.4 or ISO 10816/20816, measure at commissioning, and keep the baseline. Vibration only means something when compared with a known-good reading.

Section 13

Energy and life-cycle cost

Pumping is typically the largest single electrical load in a water utility and the second largest in a wastewater plant after aeration. Over a twenty-year life, energy commonly accounts for 40 to 80 % of the total cost of owning a pump; the purchase price is often under 10 %.

Wire-to-water energy and life-cycle cost

Flow L/s

Total head m

Specific gravity

Pump efficiency %

Motor efficiency %

Drive efficiency %

Operating hours per year

Currency entered prices are not converted

Electricity price EUR per kWh

Purchase and installation cost EUR

Maintenance per year EUR

Evaluation period years

Discount rate % per year

Energy price escalation % per year

Hydraulic power–

Shaft power–

Electrical input–

Wire-to-water efficiency–

Specific energy–

Annual energy–

Annual energy cost–

Life-cycle cost, present value–

Energy share of life cycle–

–

Benchmarks worth carrying in your head

Order-of-magnitude values for sanity checking a design. Actual figures vary widely with topography, water quality and plant configuration.
Process	Specific energy	Comment
Conventional surface water treatment, excluding distribution	0.1–0.4 kWh/m³	Dominated by raw water lift and high service pumping
Municipal wastewater treatment, whole plant	0.3–0.6 kWh/m³	Aeration is typically half; pumping 15–25 %
Membrane bioreactor, whole plant	0.6–1.2 kWh/m³	Membrane air scour and recirculation add substantially
Brackish water RO	0.4–1.2 kWh/m³	Strongly dependent on feed salinity and recovery
Seawater RO with isobaric energy recovery	2.5–4 kWh/m³	Without energy recovery, roughly double
Sewage lift per 10 m of lift	~0.04 kWh/m³	At about 70 % wire-to-water efficiency

Where the energy actually leaks

Oversizing and throttling. A control valve dissipating 15 m of head is a heater. If a pump is permanently throttled, trim the impeller or fit a drive.
Running left of BEP. Efficiency falls, and so does reliability, so the cost appears twice.
Worn clearances. Open impeller front clearance and closed impeller wear rings both leak internally as they wear; several efficiency points are commonly recoverable by restoring clearances.
Unnecessary recirculation. RAS and mixed liquor recycle rates set once at commissioning and never revisited are a widespread, invisible energy cost.
Parallel pumps on a friction-dominated system. Each additional pump adds less flow and more head loss; sometimes one larger pump at BEP beats three small ones fighting each other.
Regulatory floors. Minimum efficiency requirements now apply to many pump types — the US Department of Energy pump energy index and the EU minimum efficiency index under Regulation 547/2012 — but they are floors, not targets.

Section 14

Failure modes and what they actually mean

Symptoms in pumping are ambiguous: the same noise has several causes, and most of them trace back to the system, not the machine.

Symptom	Likely causes	First checks
Gravelly rattling noise, fluctuating discharge pressure	Classic suction cavitation from insufficient NPSH margin; blocked strainer; closed or partly closed suction valve; liquid warmer than assumed	Measure suction pressure at the flange while running; recalculate NPSHa at the actual flow, not the design flow
Noise and vibration only at low flow	Suction recirculation; operating far left of BEP; minimum flow not respected	Measure flow; compare with the curve and the minimum continuous stable flow; look for impeller eye damage on the pressure side of the vanes
Erosion damage on the impeller outer edge and the volute cutwater	Discharge recirculation, usually from operating far left of BEP, or excessive cutwater clearance	Check duty point against BEP; check the impeller-to-cutwater gap, typically 4–6 % of impeller diameter
Flow steadily declining over months	Wear ring or front clearance opening up; impeller wear; pipe fouling; valve drifting shut; rising static in the receiving system	Take a field performance test: flow, suction and discharge pressure, power. Compare with the original certified curve
Pump will not prime, or loses prime	Air leak on the suction side; high point in the suction line; vortexing from low submergence; entrained gas in the product; loss of foot valve	Pressure-test the suction line; check wet well level against the required submergence; look for a whirl at the surface
Repeated seal failure within weeks	Dry running; abrasives in the seal chamber; flush plan not commissioned; crystallisation on the atmospheric face; shaft deflection from operating far from BEP	Verify the flush is actually flowing and at the right pressure; check duty point; check shaft runout and seal chamber type
Motor trips on overload	Running out to the right on a low-resistance system; liquid denser or more viscous than assumed; mechanical rub; for axial pumps, running at abnormally low flow	Measure power and flow together; check specific gravity and solids content against design
Bearings failing with fluting or frosted races	Electrical discharge from a variable speed drive without shaft grounding; also possible misalignment or pipe strain	Fit a shaft grounding ring or insulated bearing; check alignment cold and hot; check nozzle loads
Blockage every few days at a sewage station	Rag accumulation at the impeller leading edge; wet well solids mat; pump loitering at low speed; impeller type unsuited to modern wipes	Inspect for roping rather than for large solids; review VFD minimum speed and flush cycle; consider a self-cleaning or chopper hydraulic
Sudden loss of output on a digester loop	Gas binding from entrained biogas; struvite blockage; rag at the cutter	Vent the casing high point; check suction submergence; inspect for crystalline deposits
Vibration appearing at one particular speed only	Structural or rotor resonance excited by the drive; vane passing frequency coinciding with a natural frequency	Run a speed sweep with vibration measurement; programme skip frequencies; check baseplate grouting
Pump runs but delivers nothing on a high-static system	Speed below the point where the pump curve intersects the system curve; closed valve; wrong rotation	Calculate minimum useful speed; verify rotation direction against the casing arrow; confirm valve position

Field testing beats opinion. Three measurements — suction pressure, discharge pressure and electrical power, taken simultaneously with a flow reading — locate the pump on its curve and settle most arguments. Take them at commissioning and keep the record; a pump without a baseline can only be assessed by disassembly.

Section 15

Specification checklist

What a supplier needs in order to quote the right machine, and what a reviewer should look for before approving it.

Process and duty

Service name and tag number
Minimum, normal, design and maximum flow
Total head at each of those flows, with the system curve attached
Static head range, minimum and maximum
Suction source, level range, and NPSH available at maximum flow
Number of pumps, duty and standby arrangement, parallel operation
Operating pattern: continuous, intermittent, starts per hour

Liquid

Description, specific gravity, viscosity or rheology
Temperature range, vapour pressure
Total solids percentage and type; maximum particle size; fibre and rag content
Abrasives: concentration, hardness, particle shape
pH range, chloride, sulphide, ammonia
Dissolved or entrained gas
Scaling and crystallisation tendency
Cleaning chemicals the pump will see

Mechanical

Pump type and standard: ASME B73.1, ISO 2858/5199, API 610 type, or submersible
Materials for casing, impeller, shaft, sleeve, wear rings, fasteners
Seal arrangement, API 682 category and flush plan, barrier fluid
Impeller type, free passage, and maximum and minimum diameters
Bearing type and rated L10 life
Coupling, guard, baseplate and grouting
Allowable nozzle loads and flange ratings
Coatings and linings, internal and external

Electrical and control

Supply voltage, frequency, starting method
Motor efficiency class, enclosure, insulation, inverter duty
Hazardous area classification and certification
Instrumentation: temperature, moisture, vibration, leak detection
Control philosophy, minimum speed, alternation, flush cycles

Testing and documentation

Performance test to ISO 9906 and the acceptance grade (1B, 2B, 3B)
NPSH test if margin is tight; string test if required
Vibration limits and measurement points
Material certificates, NSF/ANSI 61 and 372 where potable
Certified drawings, spare parts list, O&M manuals

Five questions that catch most bad selections in review. Where does the design duty sit as a percentage of BEP flow, and where does it sit on the minimum and maximum system curves? What is the NPSH margin at maximum flow, not at duty? What happens at minimum flow — is it above the minimum continuous stable flow? Has the seal flush plan been specified with a source, a pressure and a commissioning test? And does the material selection account for the cleaning chemicals as well as the process liquid?

Section 16

Standards referenced

Reference	Subject
ANSI/HI 9.6.1	NPSH margin
ANSI/HI 9.6.3	Allowable and preferred operating regions
ANSI/HI 9.6.4	Vibration measurement and allowable values
ANSI/HI 9.6.7	Viscosity correction of performance
ANSI/HI 9.8	Intake and sump design
ANSI/HI 14.6	Rotodynamic pump acceptance tests
ISO 9906	Hydraulic performance acceptance tests, grades 1, 2, 3
ISO 2858 / ISO 5199	End-suction pump dimensions and technical requirements
ASME B73.1 / B73.2	Horizontal and vertical inline chemical process pumps
API 610 / ISO 13709	Centrifugal pumps for heavy duty service; configuration types OH, BB, VS
API 682 / ISO 21049	Shaft sealing systems and flush plans
NSF/ANSI 61 and 372	Drinking water system components and lead content
IEC 60034-30-1	Motor efficiency classes IE1 to IE5
NEMA MG1 Part 31	Inverter-fed motor requirements
ISO 10816 / 20816	Mechanical vibration evaluation
ATEX 2014/34/EU, IEC 60079, NEC Art. 500	Equipment for explosive atmospheres, relevant to digester and biogas areas
NFPA 20	Stationary fire pumps
EU Regulation 547/2012, US DOE 10 CFR 431 Subpart Y	Minimum pump energy performance
ASTM A48, A536, A532, A743/A744, B367	Cast iron, white iron, corrosion-resistant castings, titanium castings

Selection wizard

Where each pump sits

Hydraulic fundamentals that decide the selection

The four curves

Head, not pressure

Build the system curve as an envelope, not a line

NPSH: the margin, not the match

Specific speed sets the impeller shape

Affinity laws and their limits

A selection workflow that survives commissioning

Define the flow set, not a flow

Fix the duty and standby philosophy before sizing

Characterise the liquid honestly

Build the system curve envelope

Choose the pump family from the liquid and the specific speed

Select the hydraulic against BEP, then re-check both ends

Specify materials, sealing and bearings for the liquid and the atmosphere

Size the motor and drive, then design the control

Check the transient, the intake and the noise

Pump families and where each one belongs

When a centrifugal pump is the wrong machine

Impellers, solids passage and the rag problem

Shear: when moving the liquid damages the process

Duty sheets, stage by stage

Sludge and mixed liquor: why clean-water curves mislead

Correction one: pipe friction

Correction two: pump performance

Materials of construction

Metals

Non-metallics and linings

Elastomers — the part that is usually specified last and fails first

Shaft sealing

Flush plans worth knowing (API 682 numbering)

Face materials

Motors, drives and control

Motor sizing

Variable speed drives: where they pay and where they do not

What a VFD requires of the rest of the installation

Control strategy by duty

Protection to specify, not to assume

Intakes, sumps and pipework

Suction pipework rules

Wet wells and sumps

Discharge pipework and transients

Energy and life-cycle cost

Benchmarks worth carrying in your head

Where the energy actually leaks

Failure modes and what they actually mean

Specification checklist

Process and duty

Liquid

Mechanical

Electrical and control

Testing and documentation

Standards referenced