Pipe Flow · Head Loss · Self-Cleansing · DN / NPS / Bore · Units

Pipe Hydraulics, Sizes & Units

One page, one set of pipe data: a calculator that sizes and checks pipes on their real bores, a size reference with the actual bore of every size, schedule and pressure class, and unit conversions for the quantities used in water engineering.

Sizing works on real bores, not DN numbers. Pressure flow: Q = v·A, hf = λ·(L/D)·v²/2g with λ from Colebrook–White, hj = Σζ·v²/2g. Gravity flow: Colebrook–White on the part-full section (Dh = 4R, ks for the pipe in service; Manning optional), checked against EN 752 self-cleansing and bed shear stress. Every calculation has a link that restores it.

01 Flow, velocity, bore

Bores come from the Pipe sizes view — open it to compare every size and class of this material.
m³/h
m/s

02 Velocity check

Owner, municipal or project limits in m/s. The minimum size of the duty still applies.
—
Enter flow and velocity or pipe size.

03 Head loss · friction + fittings

m
1.00 up to 20 °C (PE) / 25 °C (PVC-U). Above that, take fT from EN 12201-1 Annex A or EN ISO 1452-2 Annex A (pipe only; fittings may differ).
Reducer / expander — ζ is defined on the small-side velocity and rescaled to the current bore. Count it here only, not in the list or additional Σζ.
mm
mm
no.
Override ζ

04 Segment & calculation report

Start node (upstream)
End node (downstream)
Node ID
Description
Elevation z, mPipe invert (gravity) or pipe centreline (pressure), same datum
Pressure p, bar(g)Pressure flow only — enter the start value; the end value is computed
—
Project & document
A4 calculation sheet built from the current inputs. Printing from the Calculator view prints the report.
Save & reproduce
Calculation ID —
The link in the address bar always carries the full calculation — bookmark it, paste it into an e-mail or print it in the report (section 9). Everything is also remembered in this browser. Nothing is sent to a server.

Reproducing a calculation. The address bar always carries the complete calculation after #s=; the report prints this link and an ID in section 9, so a checker can reopen exactly what was calculated. Export JSON saves the same data as a file for archiving with the project; Import JSON loads it back. The calculation core is a separate script block in this page and is covered by a regression test run against textbook values.

Reading the results. In “size the pipe” mode the required bore is rounded up to the next size that exists in the selected material and class, and all checks run on that real bore. For pressure flow the size follows from the target velocity. For gravity flow the size follows from slope, roughness (ks or n) and the maximum design depth; the velocity input is then not used, because a part-full pipe's velocity is set by its slope. Node elevations in section 04 give the end-node pressure for pressure flow and a cross-check of the slope for gravity flow; intermediate high points are not evaluated. PASS means every active check is met; CHECK means a recommended value is exceeded or the method is near its limit; FAIL means a hard limit is broken.

Where the numbers come from. Bores: the Pipe sizes view of this page (ASME B36.10M, EN 10255, ISO 2531 / EN 545 with ISO 4179 lining, EN 12201 / ISO 4427, EN ISO 1452). Friction: Darcy–Weisbach with Colebrook–White, iterated from Swamee–Jain; λ = 64/Re below Re 2300. Fitting coefficients are cross-checked between Crane TP-410, Idelchik's Handbook of Hydraulic Resistance, Blevins and published manufacturer tests (to EN 1267); tick “show reference ranges” to see the spread. With size scaling on, Crane's fT is computed from the Nikuradse fully-rough formula for clean commercial steel (ε = 0.046 mm) at the fitting bore, which matches the printed Crane table within rounding; the pipe material does not enter, because the loss occurs in the fitting body. Gravity: circular part-full geometry with Colebrook–White on the hydraulic diameter 4R (the EN 16933-2 / HR Wallingford method; ks 1.5 mm for foul sewers and 0.6 mm for clean pipes represent the pipe in service), Manning as an alternative; minimum self-cleansing velocity 0.7 m/s per EN 752 (the velocity criterion is common practice up to about DN300; larger sewers are assessed on shear stress); bed shear stress τ = ρ·g·R·i against your threshold. The recommended-velocity bands by medium and duty are Polarlys Innovation's own design table, compiled from practice — they are guidance, not a standard; a project requirement entered in section 02 replaces them. The calculation ID in the report is a fingerprint of every input; the link restores them all.

Cautions. Between Re 2300 and 4000 no correlation holds; the tool shows the laminar–turbulent spread and the result should not be used for design. Sludge above about 4 % DS and polymer solutions are non-Newtonian — friction is not computed for them, and the viscosity correction for 1–4 % sludge covers only the Newtonian term, not yield stress. Check gravity sewers twice: self-cleansing at the daily peak dry-weather flow, capacity and depth at the design peak. Maximum depth and minimum shear stress are set nationally or by the municipality, not by EN 752. Friction loss shown for a gravity pipe assumes it runs full under pressure and is for reference only. The steel rating is an indicative hoop-stress value; ductile iron uses the EN 545 PFA for K9, which falls with DN; PVC-U at de ≤ 90 is rated one PN class lower than the same SDR above de 90. Surge is not included anywhere.

Polarlys Innovation AS — water and wastewater engineering, Trondheim, Norway. Org. no. 820 776 402. [email protected]

Editorially independent. No supplier or product recommendations.

Provided for reference and preliminary design. Not a substitute for engineering design or a check against the governing standard. © Polarlys Innovation AS

Calculation report — preview