Rotating equipment — NPSH
Net Positive Suction Head margin (cavitation)
Computes NPSHa from the system + fluid properties and compares against the pump's NPSHr. Catches cavitation before it eats the impeller. The check every centrifugal-pump engineer does on every selection.
Inputs
bar
Atmospheric for open tank; vessel pressure for closed system
m
Positive if source is above pump centerline; negative for suction lift
m
Pipe friction + fittings + filter on the suction side
°C
m
From manufacturer's curve at the rated flow rate
m
API 610 §6.1.13 typical: 1.0 m for hot service · 0.5 m cold
P_v from IAPWS-IF97 steam tables
Results
ρ at T998kg/m³
P_vapor at T (interp.)2.34kPa
(P_surf − P_v) / (ρ·g)10.11m
+ Z_static − h_friction0.50m
NPSHa available10.61m
NPSHr (pump curve)3.50m
Margin (NPSHa − NPSHr)7.11m
Margin (% NPSHr)203 %
VerdictCONSERVATIVE — comfortable margin
NPSH balance
NPSHa10.61 m
NPSHr3.50 m
min margin0.50 m
API 610 11th ed. §6.1.13: NPSHa ≥ NPSHr + 1.0 m for hot service (T > 65 °C). Cavitation onset begins at NPSHa = NPSHr by definition; 3 % head-drop occurs slightly above. For fatigue-prone applications (cooling-water duty cycle) increase margin to 1.5-2 m.
Download all inputs + calculations + outputs as a single PDF.