Pump Hydraulics
Suction, power, and selection — graded against the rules the industry actually uses.
NPSH Margin
Compute NPSH available from suction conditions and grade the margin against the required NPSH. The margin rule is service-dependent.
Margin of 29.4 ft meets the max(1.0 m, 1.1×NPSHr), general/petroleum service. The margin rule is service-dependent — confirm against the pump vendor curve.
- General / petroleum≥ 3.28 ft (1.0 m) / 1.1×
- Chemical≥ 1.97 ft (0.6 m)
- Boiler feed≥ 0.3×NPSHr
NPSHa = Hsp + Hss − Hvp − Hsf, all in ft of liquid (H = 2.31·P/SG).
Pump Power
Water horsepower, brake horsepower, and kW from flow and head, plus the next standard NEMA motor size.
70–80% is normal for mid-size centrifugal pumps near BEP.
WHP = SG·Q·H/3960; BHP = WHP/η; kW = BHP·0.7457. Motor is the next NEMA HP above BHP — add service factor margin for continuous duty.
Affinity Laws
Project a new duty point for a speed change or impeller trim: Q∝r, H∝r², P∝r³.
Projection is within the reliable affinity-law range. Re-check NPSHr at the new point.
Trim ratios below 0.80 lose accuracy and efficiency. Always re-check NPSHr at the new point — it does not scale with the affinity laws.
VFD Savings (Static-Corrected)
Honest annual savings range for a VFD retrofit. Splits head into static and friction so the cube law doesn't overstate the payback.
40% static head means real savings fall between the cube-law and static-corrected bounds. Quote the range, not the best case.
Quote the low (static-corrected) figure for proposals. The cube law only holds for friction-dominated systems; static head sets a power floor a VFD cannot beat. Payback ≈ installed VFD cost ÷ annual savings.
Minimum Continuous Flow
Estimate the minimum flow needed to keep the pump's temperature rise within an allowable limit.
Keep flow at or above 14 gpm to limit temperature rise. Add a recirculation or ARC valve if the process can throttle below this.
Q_min ≈ BHP/(2.95·Cp·SG) for a 15°F rise, scaled by the allowable ΔT. Most of the brake power at shut-off becomes heat — protect the pump with a recirculation line below this flow.
Cavitation Diagnostic
Check the symptoms you observe; the tool points to the most likely cause and the next check to run.
Choose the observed symptoms to identify the most likely cause.
If cavitation is indicated, run the NPSH Margin tool next. Recirculation points to raising flow above minimum continuous flow; air entrainment to suction integrity; wear to a mechanical inspection.
Specific Speed
Classify the impeller from specific speed (Ns) and gauge low-flow stability from suction specific speed (Nss).
Specific speed Ns ≈ 913. Suction specific speed (Nss) is a risk index, not a pass/fail — high Nss widens the unstable low-flow window.
- Radial< 2000
- Francis / mixed-radial2000–4000
- Mixed flow4000–9000
- Axial flow> 9000
Nss above ~11,000 widens the unstable low-flow window — treat it as a risk index, not pass/fail.
Pump Selection Summary
Roll system inputs into a vendor-ready spec sheet: duty flow, total head, NPSH margin, and brake power.
Duty point, TDH, NPSHa, and BHP are assembled. Send to the pump vendor to confirm against real curves and NPSHr.
TDH = static lift + friction. BHP = SG·Q·TDH/3960/η. Send this summary to the pump vendor to confirm against real performance curves and tested NPSHr.
Piping & Hydraulic Transients
Velocity, pressure drop, wall thickness, and the transients that wreck a line.
Pipe Velocity & Size
Pick the smallest Schedule-40 line that keeps liquid velocity inside the recommended band for the service.
7.6 ft/s is within the 5–10 ft/s guideline for discharge service.
v = 0.4085·Q/ID² (Schedule 40 steel). Keep suction lines slow to protect NPSH; discharge can run faster. Higher velocity means more friction and erosion.
Liquid Pressure Drop
Darcy-Weisbach friction loss for liquids with a Swamee-Jain friction factor — distinct from compressed-air drop.
8.38 psi/100 ft is steep — pump head and energy cost climb fast. Size up the pipe.
Re = 3160·Q·SG/(ID·cP); laminar f = 64/Re below Re 2300, otherwise Swamee-Jain. hf = f·(L/D)·v²/2g, converted to psi via 0.433·SG. Add fitting losses before sizing the pump.
Wall Thickness (B31.3)
Minimum wall per ASME B31.3 process piping using the full code form — then the lightest standard schedule that meets it.
The selected schedule clears the ASME B31.3 minimum with margin. This is NOT a Barlow estimate — the full code form (Y, E, W) is used.
t = P·D / (2·(S·E·W + P·Y)), Y = 0.4, W = 1.0. This is the full B31.3 form — NOT the Barlow thin-wall approximation, which under-predicts for thick or high-pressure pipe. Confirm mill tolerance (−12.5%).
Fitting Losses
Total the minor losses from valves and fittings into a head loss and an equivalent length of straight pipe.
Head loss = ΣK·v²/2g; equivalent length = ΣK·D/f (f ≈ 0.02). K-factors are for fully-open valves — partially closed valves rise sharply.
Thermal Growth
Axial growth of a pipe run from ambient to operating temperature, plus a first-cut expansion-loop leg length.
≈2.70 in — an expansion loop or bellows is required to avoid overstressing anchors and nozzles.
Growth = rate(in/ft)·length, measured from 70°F ambient. Loop leg L ≈ 6·√(D·Δ) for Sch-40 carbon steel — a starting point, not a stress analysis. Confirm anchor and guide loads.
Pipe Support Span
Maximum spacing between pipe supports for a given size, service, and insulation.
Space supports no more than 45 ft apart. Bending stress and sag (≤9000 psi / typ. ¼ in) govern — shorten for valves or concentrated loads.
Spans are water-filled, straight-run values where bending stress (≤9000 psi) and sag govern. Shorten at valves, flanges, and concentrated loads. Empty/gas lines allow a bit more; insulation a bit less.
Compressed-Air Pipe
Size an air main, drop, or branch on the air-velocity convention, with a pressure-drop-to-energy-cost note and receiver tie-in reminder.
SCFM is converted to ACFM at line pressure before sizing. Tie new headers into the receiver, not a compressor discharge, and keep total distribution drop under ~10% of system pressure. Every ~2 psi of artificial demand adds about 1% to energy cost.
Water Hammer
Joukowsky pressure surge from valve closure, the critical closure time, and a safe minimum closure time.
Closure (2.0 s) is well above the critical time (0.21 s). Surge is limited to a fraction of full Joukowsky.
Wave speed a ≈ 4720 ft/s (water in steel, simplified). ΔP = ρ·a·Δv. Closing faster than 2L/a gives the full Joukowsky surge — add slow-close actuation, a surge tank, or relief on long lines.
Pump Check Report
Roll NPSH, power, affinity trim, and VFD savings for one duty point into a branded one-pager.
Pump Check Report
Bundle NPSH margin, pump power, affinity trim, and VFD savings for one duty point into a branded one-page summary.