Understanding NPSH for Centrifugal Pumps

LANGFANG, China - June 10, 2013 - PRLog -- Fluid flows from areas of high pressure to areas of low pressure.Centrifugal pump operate by creating low pressure at the inlet which allows the liquid to be pushed into the pump by atmospheric or head pressure. Consider placing a pump at the top of a mercury barometer above: Even with a perfect vacuum at the pump inlet, atmospheric pressure limits how high the pump can lift the liquid.With liquid lighter than mercury,This lift height can increase,But there's still a physical limit to pump operation based on pressure external to the pump. this limit is the key consideration for Net Positive Suction Head.
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The definition of NPSHA is simple: Static head + Surface pressure head-the vapor pressure of your product-friction losses in the piping,valves and fittings.
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But to really understand it, you first have to understand a couple of other concepts:
1,Cavitation is what net positive suction head (NPSH) is all about, so you need to know a little about cavitation.
2,Vapor Pressure is another term we will be using.The product's vapor pressure varies with the fluid's temperature.
3, Specifica gravity plays an important part in all calculations involving liquid. you have to be familiar with the term.
4, You have to be able to read a pump curve to learn the NPSH required for your pump.
5, You must know the difference between gage pressure and absolute pressure.

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