Effect of Suction Dampeners on NPSHr (recip technology) 1

[GaTechTheron]

I actually have 2 issues.

1)Our pump manufacturer cannot give me a hard number for NPSH because they say it has to be tested. Infact, they claim to be able to take the NPSHr from a compeditors similar pump, add a foot or 2, and then have a "good" approximation.

I do not consider this a good approach, especially when NPSHa is within 2 ft of NPSHr. Does anyone know of a better way to approximate this?

2)We are not taking into consideration the effect of the suction dampeners on NPSHr. I know these should have a very good effect on acceleration head, but I'm not sure how much. Is there a way to approximate this as well?

My Cameron Hydraulic book will only take me so far.... All help is greatly appreciated.

 

[CH5OH]

a pump manufacturer should be able to provide you with that data.test:take pump to best efficiency point shoke inlet valve untill discharge pressure dropped 5% of best efficiency point.for npsh test there are even standards(API,...)

 

[GaTechTheron]

Thank you for the reply.

Allow me to be more clear. I'm looking for a way to determine how much acceleration head will be reduced by including a suction dampener. We will run the test, but I don't want to buy a Pump... THEN find out it will require to much NPSHr

 

[stanier]

You need to invest in the book The Reciprocating Pump Theory Design and Application by Miller published by Kreiger.

NPSHa will specificaly have to take into account acceleration of the fluid.

NPSHr of pump does have to be tested by the manufacturer as it depends on the losses through the inlet valves, manifold and other devices on the suction side.

Alternatively you could model the pump using a transient analysis program such as AFT's Impulse.

http://www.aft.com.

 

[SNORGY]

I have seen pulsation dampener vendors claim up to 95% attenuation in pulsations, whereas in practice, the observed attenuation was 50% or less.

Some vendors give you some overview level equations that you might apply (google Hydril of Coors-Tek) but to date I haven't had much luck with getting anything useful or accurate out of them.

Stanier, thanks for the tip, I will try to locate that book.

Regards,

SNORGY.

 

[curtis26]

I have not read The Reciprocating Pump Theory Design & Applications, but I think that sound like the most sound advice that I have read.

My advise if you are with in 2 feet of the NPSHr estimate of the pump is to use a centrifugal charge pump (it will likely be cheaper than paying for the manufacture to do the NPSHr test) and on a recip pump you can probably supply 3-4 times the NPSHr with out hurting anything. Also, the manufacture will likely require for you to have something like 7 feet NPHSa over the NPSHr or 150% NPSHa over the NPSHr anyways.

While we know the dampeners do reduce NPSHa loss due to acceleration head they do not change the NPSHr. The use of dampeners during the NPSHr test increase the accuracy of the test results. You might be able to do an NPSHr test on a pump with low flow variation like a quintuplex for example (7.1 flow variation) with out dampeners and get good results, but if you try to do the test on a double duplex pump (45.6%) the pressure gage is going to be bounce all over the place and the readings you take will likly have a standard error that exceed the 2 feet differential you are trying to test.