Question

(d) A centrifugal pump delivers 1000 Ls-1 of water at a head of 3 m and speed of 60 rpm. Determine the Net Positive Suction Head Required.

Answer is [NPSHR = 0.196 m]

How do i do this?

Answer 1

Suction Specific Speed is an index that describes the characteristics of the suction side of the impeller. It is calculated using the NPSHr in feet, speed (N) in rpm, and flow rate (Q) in gpm at the pump’s Best Efficiency Point and maximum impeller diameter. The equation for Suction Specific Speed (designated Nss or S) is:

Nss=N×Q^0.5/NPSHr^0.75

Where:

Nss = Suction Specific Speed (unit-less)= 9000 (assume value)

N = Speed in rpm= 60 rpm

Q = Flow rate in gpm= 1000 l/s = 15850.32 gpm

NPSHr = measured in feet

Nss values for many standard impellers typically range from 7000 to 9000, but some designs may have a Nss as high as 18,000 to 20,000.

9000 = 60× (15850.32)^0.5 / NPSHr^0.75

NPSHr^0.75 =0.83932

NPSHr = 0.7917 ft

NPSHr = 0.2413 mts

Please provide the exact Nss Value to achieve your answer.