Hydraulic Significance of NPSHA in Pump Operation:

• Acronym Definition: NPSHA stands for Net Positive Suction Head Available.
• Engineering Definition: It represents the absolute hydraulic head available at the pump suction nozzle above the vapor pressure of the liquid:
  $$\text{NPSHA} = h_{\text{atm}} + h_s - h_f - h_{\text{vp}}$$
  To prevent destructive cavitation, the system's available suction head must strictly exceed the pump's required suction head ($\text{NPSHA} \gt \text{NPSHR}$).

Pump Characteristic Curves and Efficiency Analysis:

• True Operating Facts:
• For standard backward-curved centrifugal pumps, the head-capacity ($H-Q$) curve slopes downward; head decreases as discharge increases.
• Shut-off head occurs at $Q = 0$ when the delivery valve is completely shut.
• The pipe thickness and pressure rating must withstand maximum hydrostatic pressure at shut-off head without bursting.
• Statement 4 is completely False: Pump hydraulic water horsepower is proportional to discharge: $\text{WHP} = \frac{\gamma Q H}{75}$. At shut-off head, because $Q = 0$, useful water power output is zero, and therefore pump efficiency is exactly ZERO ($\eta = 0\%$), not maximum! Maximum efficiency occurs at the Best Efficiency Point (BEP) at intermediate design flow.

Application of Pump Affinity Laws for Rotational Speed:

• Affinity Law Formulation: For a given centrifugal pump of fixed impeller diameter, developed head ($H$) is directly proportional to the square of rotational speed ($N$):
  $$\frac{H_2}{H_1} = \left(\frac{N_2}{N_1}\right)^2$$
• Given Parameters:
• $N_1 = 1,500\text{ RPM}$
• $H_1 = 10\text{ m}$
• $N_2 = 1,650\text{ RPM}$
• Computation:
  $$\frac{N_2}{N_1} = \frac{1,650}{1,500} = 1.1$$
  $$H_2 = H_1 \times (1.1)^2 = 10 \times 1.21 = 12.1\text{ m}$$