Recommended NPSH Margin according to ANSI / HI guideline
NPSH margin = NPSHa ‐ NPSHr
NPSH margin ratio = NPSHa / NPSHr
Hydrocarbon (Petroleum) process pumps
minimum margin ratio of 1.1 or minimum margin of 1 m
whichever is greater. (Within the AOR ‐ allowable operating
range)
Chemical process pumps
Suction specific speed range
Below 210 metric or 11000 US unit
Above 210 metric or 11000 US unit
NPSH margin ratio or margin
NPSH margin ratio 1.1 or margin 0.6 m whichever is greater within AOR
NPSH margin ratio 1.1 or margin 0.6 m whichever is greater within POR
NPSH margin ratio 1.2 or margin 1 m whichever is greater outside POR
Power Plant pumps (Non‐nuclear)
Water / wastewater pumps
Pulp and paper stock pumps
Suction specific speed range
Below 145 metric or 7500 US unit
Above 145 metric or 7500 US unit
NPSH margin ratio or margin
NPSH margin ratio 1.1 or margin 0.6 m whichever is greater
NPSH margin ratio 1.2 or margin 1 m whichever is greater
HVAC and other building services pumps
Suction specific speed range
Below 145 metric or 7500 US unit
Above 145 metric or 7500 US unit
NPSH margin ratio or margin
NPSH margin ratio greater than 1 throughout AOR
NPSH margin ratio 1.1 or margin 0.6 m whichever is greater