Which of the following operational modifications will INCREASE the Net Positive Suction Head Available ($ ext{NPSH}_A$) of an agricultural irrigation pump?
Options:
(A) Lowering the pump closer to the water level in the sump (reducing static suction lift $h_s$)
(B) Increasing the diameter of the suction pipe to decrease frictional head loss ($h_{fs}$)
(C) Installing a foot valve with an unrestricted, streamlined strainer
(D) Pumping water at higher temperatures near boiling
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
- A, B, and C decrease suction line losses and suction lift, increasing $\text{NPSH}_A = \frac{P_{\text{atm}} - P_v}{\gamma} - h_s - h_{fs}$.
- D increases vapor pressure $P_v$, which severely reduces $\text{NPSH}_A$ and induces cavitation.