How much is the different margin of NPSH should be?

[chonglom]

Is there any rule of thumb or standard that specified how much NPSHa - NPSHr should be? Thanks

 

[quark]

pump-zone

Goulds

 

[Latexman]

I've seen companies use ratios and margins. They also make a distinction on the type of application, like process, utility, cooling water. Using a maximum flow design case, a 3 ft margin and NPSHa/NPSHr = 1.1 is common for process and utilities. On cooling water, I've seen a more conservative ratio of NPSHa/NPSHr = 1.2.

Good luck,
Latexman

 

[JJPellin]

We use a margin of 3 feet or 15% on hydrocarbon services and 5 feet or 15% on water services. We are considering increasing the margin requirements.

Johnny Pellin

 

[25362]

Thread407-232673 brings an interesting discussion on the subject.

 

[MJCronin]

chong....

As stated by 25362, the best and most authoritative source of information on NPSHA margin is Hydraulic Institute Standard 9.6.1

You should note that the suggested margin is based on the expected pump and system operating conditions. A cooling tower pump has a higer margin than a chemical plant process transfer pump.

 

[BigInch]

NPSHa > NPSHr

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