NPSHr “ Net Positive Suction Head

✳️ NPSHr “ Net Positive Suction Head Required “ at the first stage impeller to ensure successful Pump operations.

📌 NPSHr is determined by the manufacturer with hydraulic testing. It is not determined by the system design – that would be NPSHa, or the net positive suction head available. NPSHa must always be > NPSHr to avoid the cavitation phenomena.

✳️ Min. Submergence is the amount of liquid required above the pump’s suction pipe to prevent a vortex from being created which can cause air entrapment and pre-rotation. The min. submergence is determined by the factory using a formula that is based upon the geometry and flow characteristics of the pump.

✳️ If the system characteristics do not meet the submergence or NPSH requirements of the pump, cavitation can occur in either case. If a vortex forms because the liquid level is too low, air can enter the pump and cause damage to the pressure changes. If there is not enough suction head available, the fluid pressure will fall below its vapor pressure inside the pump, leading to bubble formation & collapse(Cavitation).

✳️ To satisfy the Min. Submergence requirement, just add more liquid! In order to avoid NPSHr issues, you can add liquid, add pressure to the suction source, or reduce frictional losses in the suction system.