Suction pressure in pump operations is defined as what, and why does it matter?

• A. It is the suction side pressure and must be positive to maintain prime.
• B. It is the discharge side pressure and must be positive.
• C. It is the downstream pressure after the nozzle.
• D. It is the ambient atmospheric pressure around the pump.

Answer: (B)

Suction pressure is the pressure at the pump’s inlet (the suction side). It matters because the pump needs water to be drawn into the impeller, and having positive pressure at the inlet relative to the water’s vapor pressure keeps the water in liquid form and preserves prime. If suction pressure drops toward zero or becomes negative, cavitation can occur, reducing flow, causing damage, and risking loss of prime. So suction pressure being positive at the inlet is essential for reliable priming and proper pump operation.