NPSH for plunger pump

[jawadkikar]

Hi
please what is NPSH for plunger pump have the folloing data sheet:
LIQUID PUMPED:Condensate
SP. GR. @ PT:0.071
VAPOR PRESS. @PT:0.96
VISCOSITY @PT:0.66
NORMAL ATMOSPHERIC PRESS.: 0.96 bara
MAXIMUM CAPACITY @ PT: 2 m3/hr
DISCHARGE PRESSURE: 65 bara
SUCTION PRESSURE: 0

please to inform me the equation which determine the required NPSH

regards

 

[micalbrch]

NPSHR is something you can only get from the pump manufacturer. If you give us pump model and manufacturer or perhaps plunger diameter and stroke length, we will perhaps be able to make a guess (with some risk) but nobody here can calculate NPSHR of your pump.

 

[jawadkikar]

thanks
but can I calculate NPSHA


regards

 

[micalbrch]

Yes, of course you can. But you need some more information about the suction side installation to do this.

You can search here in the forum or just "NPSHA calculation" through Google and you will find all required information plus calculation formula.

 

[JJPellin]

In order to evaluate the cavitation potential for a piston pump, you have to know the stroke rate and suction line length. With a piston pump, the acceleration head can be quite significant.

Johnny Pellin

 

[btrueblood]

Need RPM too...

 

[jawadkikar]

thank you for your co-operation, but please what is the exact equation?


regarsd

 

[vpl]

Does "Bernouli" ring a bell?

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[25362]

You may find an answer to your queries in Pump Handbook McGraw-Hill, by Karassik et al., in the chapter: Displacement Pumps.

BTW, SP Gr. seems to be a typing error.

Good luck.

 

[jawadkikar]

thanks for all

 

[micalbrch]

For NPSHA calculation see:

http://www.engineeringtoolbox.com/npsh-net-positive-suction-head-d_634.html

What needs to be added to the NPSHA calculation formula for centrifugal pumps is the suction side acceleration head which is (L x v x n x c)/(k x g) where L is the suction pipe length, v is the fluid velocity, n is the stroke rate of your plunger pump, c is the pump factor (0.066 for a triplex pump), k is a correction factor for laminar flow (= 1.5) and g is the acceleration of gravity. The result must be deducted from the NPSHA result for centrifugal pumps.

 

[btrueblood]

Mical's equation is ok, but if you operate near the limit of suction head, or are comparing different pumps, you need to look at details of the pump construction, finding peak velocity or acceleration (depends on bore, stroke, rpm) through the smallest flow area (typically check valves). Peak velocity is affected by no. of cylinders, with 3, 5, 7 etc. giving better performance than 1, 2, 4, 6.

 

[chicopee]

To facilitate the understanding of the relationshp of NPSHA with inlet conditions to the pump, I am attaching one of my several examples that I have worked out in the past. Note the diagrams on the right side of the page showing these relationships.

 

[BigInch]

Its kinda' faint, but I don't see where you've included acceleration head there. Looks to be for centrifugals only.

 

[chicopee]

You mean velocity head. It could be included on the supply side,however for many systems,it would be too small of a value. There is a velocity head at the pump inlet in my attachment.
Same first law would apply on the inlet side of the plunger pump for only about half of its cycle.

 

[micalbrch]

No, he meant acceleration head and it is usually not a small value for multiple plunger pumps unless they have a suction side flow stabilizer (pulsation dampener) - and most of them haven't.

 

[ione]

It is definitely acceleration head. Piston pumps are characterized by pulsating flow (acceleration and deceleration are typical of reciprocating pump), which affects the value of NPSH.

Suggest to give a read

http://www.pump-zone.com/pumps/centrifugal-pumps/acceleration-head.html

 

[chicopee]

Thanks for the info. Biginch,micalbrch and ione

 

[BigInch]

reminds me of the 3 musketeers.
"For Ione and all."

 

[ione]

This motto sounds better: “All for Big and Big for all”