How can we explain easily to our customers what are NPSH available and NPSH requested? Most of them are not familiar with these data...

NPSHR("required", NOT "requested") is the amount of NPSH required by the design and manufacture of a specific pumping unit at a given flow rate and pump speed.
NPSHa("available") is the amount of remaining atmospheric pressure available at the suction inlet of the pump; this is a function of suction pipe design, site conditions, and suction side friction losses at a given flow rate(if any.)

Simply speaking - NPSHA is what you have, NPSHR is what you need!

NPSHr means the suction head Which pump needed, and NPSHa means the head which the system supply to pump.

When NPSHr is greater than NPSHa, it is good for the pump supplier and bad for the customer as the pump will require replacement parts or replacement pumps on a regular basis. Cavitation is the most effective way to distroy a pump and is almost never understood by customers. Ensure your sales team has a good handle on pump systems and the effects of flow rate of NPSHa and NPSHr to help educate your customers. This is an issue that does not have an easy answer and has been one of the most difficult concepts for me to explain to customers.

In other simple words: 1)in order to make pumping possible you need to have some pressure at the pump suction side, called AVAILABLE (which varies depending on the temperature, altitude above sea level, height above the pump suction, and the friction losses); 2) due to hydraulic design each pump has certain requirements as to the minimum suction pressure required for cavitation free pumping (trouble free pumping), also measured in meters- called REQUIRED

Can pumping problems be created by waveform distortion or form factor of supply voltage?.

I think Zhang has explained in simple terms what NPSHR and NPSHA means i.e. NPSHR is the minimum Head required by the Pump at Suction Inlet and NPSHA is the Head available at site of pump installation at Pump Inlet. NPSHA should always be more than NPSHR for trouble free pump operation.

I am disaonted that non of you my friends did not expend your explanation for the formula and gave an explanation for it's positive result or negative result .
P.S. none of you did not mention temp./vapor pressure as an importent factor .
positive suction condition / negative ( lift ) suc. condition .

As a very simple unswer for costomer , some of your ideas are not bad