Like humans, a pump also has basic needs, such as energy and nourishment. Its energy is called an adequate available supply of liquid at the suction nozzle. If the liquid is leaving the pump faster than it comes into the pump, then the pump is starved and feels hungry.

If an industrial pump is starved, the pump’s output of pressure and flow will be reduced. This will make process engineers assume that the pump is running off-its-curve. A pump running off its performance curve is considered a maintenance problem, yet it is actually a design or operation problem. This problem can be solved by astute instrumentation technicians.

Some people will say that NPSH doesn’t seem to be an accurate description for the minimum acceptable energy requirement of a pump. This is good argument. If you don’t look into the deep, the term NPSH seems to tiptoe around what it’s trying to describe. However, on further study, it’s really a good term.

With pumps, there are factors in the fluid and the suction piping that adds energy to the fluid. For example, a tank, holding liquid, supplies the suction nozzle of a pump DLLA138S1191 through a length of pipe. The liquid’s elevation in the tank, its temperature, and the pressure on the tank and liquid contains the gross energy available in the system. We could call it the Gross Positive Suction Head available. A pressure gauge at the tank’s exit pipe would record the energy in PSI after factoring the liquid’s specific gravity.

When the pump is started and the liquid begins draining from the tank into the suction piping, any movement of the liquid diverts some of the gross energy to the pump. Other energy is lost as the level drops in the tank. Other energy is consumed by the liquid’s velocity through the suction pipe and fittings. Still other energy is consumed by friction between the liquid and the internal walls of the suction pipe 8N7005 and fittings. As the liquid arrives to the pump suction nozzle, the remaining energy in the liquid is the net energy available to the pump.