V. SUPPLY SYSTEM CONSIDERATIONS
G. NPSHR (Net Positive Suction Head Required)
The NPSHR is the head of liquid, in feet, required at the centerline of the liquid end inlet/suction connection to completely fill each cylinder on the reverse/suction stroke. It is the feet of liquid necessary to;
a) overcome the frictional losses through inlet manifold, valves and liquid chamber,
b) overcome the valve weight and spring force acting on the valve,
c) overcome the valve velocity head losses,
d) accelerate the liquid from rest to required velocity.
NPSHR is a function of the liquid and pump characteristics (stroke, plunger size, liquid end design, and operating speed).
NPSHR is usually determined by test or estimated by computation. Figure 55 and 56, on pages A36 and A37 respectively, show the liquid supply system relationships for open and closed supply tanks.
