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mostafaalkholy
Commentator

Join Date: Nov 2008
Posts: 72

Centrifugal Pumps

11/05/2008 9:28 PM

IF I HAVE A PUMP (CENTRIFUGAL) WORKING IN LOW NPSH ,WHAT SHUOLD WE DO TO OVERCOME THIS PROBLEM
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ducon
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Join Date: Dec 2006
Location: Hop around Toronto, New York & Karachi
Posts: 1876
Good Answers: 19
#1

Re: HOW TO OVER COME A LOW NPSH DURING OPERATION

11/05/2008 10:30 PM

Opt for a Low NPSH Pump. Try Grundfos CR Range pumps.

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 I not only use all the brains that I have, but all that I can borrow. Woodrow Wilson
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ducon
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Join Date: Dec 2006
Location: Hop around Toronto, New York & Karachi
Posts: 1876
Good Answers: 19
#2

Re: HOW TO OVER COME A LOW NPSH DURING OPERATION

11/05/2008 10:38 PM

Go to Google "type Low NPSH" and check Hydrcarbon Processing Special Report " Consider Regenerative Pumps for low-flow/low-NPSH application" . Check out Schematic & chart on page 1. E-mail author Mr. Steve Muller at stephensmech@aol.com.

Do let me know his reply also.

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 I not only use all the brains that I have, but all that I can borrow. Woodrow Wilson
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Aly Badawy
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Join Date: May 2008
Location: Egypt
Posts: 45
Good Answers: 1
#3

Re: HOW TO OVER COME A LOW NPSH DURING OPERATION

11/05/2008 10:59 PM

Dear Mostafa

1-You have to specify your problem exactly (do you have cavitation,low discharge,....etc?).

2-Send us your pump curve.Also the liquid and its temp you are pumbing.

3- The more informations you give , the more the rapid and accurate solution you will get.

Aly Badawy
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Ed Weldon
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Join Date: Oct 2008
Location: I'm outa here
Posts: 1924
Good Answers: 196
#4

Re: Centrifugal Pumps

11/06/2008 11:49 PM

Increase the NPSHA (NPSH available) Here's the basics:

1. Reduce friction losses in suction lines. Pipe to small diameter or too long, fittings like too many elbows, foot valves, strainers, check valves, globe valves. Old clogged and corroded piping.

2. Reduce flow rate to minimum required for system perfomance.

3. Reduce vapor pressure of pumped liquid by reducing temperature or amount of light fractions in liquid mixtures.

4. Eliminate sources of air entering the suction, which can produce symptoms that sound like cavitation. Air leaks or votitices in the suction source which can drag air in. Leaking pump seals. Entrained air in the liquid in the suction tank can be reduced by submerging the tank inlet, enlarging and baffling the suction tank or reducing liquid viscosity to allow bubbles to clear more quickly.

5. Increase the static head on the suction supply. Make sure the suction supply tank is vented to atmosphere properly.

6. Some high quality industrial end suction type pumps can be fitted with an inducer, a screw-like device which replaces the impeller nut. Contact the pump manufacturer

7. Note some manufacturers offer condensate pumps for steam boilers. these pumps are specifically designed for very low NPSH service.

8. Look at slower speed pumps, which in general will be substantially larger for the same head and capacity.

9. Note that flexible nonmetallic lines on the suction side of the pump can collapse from external air pressure and increase friction losses in the suction line.

10. Add energy to the liquid in the suction line through the use of a so called "jet". These devices are common in well pumps that have to draw water from depths below 25-30 feet.

11. Note that at high elevations there will be less NPSHA, all other things being equal, due to lower atmospheric pressure. Even weather changes to lower barometric pressures can bring cavitation symptoms in a system that is just on the edge to the point where the problem becomes noticeable.

I might have missed some points; but this all should give you something to chew on.

Ed Weldon
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Anonymous Poster
#5

Re: Centrifugal Pumps

11/07/2008 6:55 AM

u should attached a series of pump to overcome the promblem. on second thought u should measure the height of pump at which place it is placed ex. if the pump height is 10m then there will be a pressure of 1kg/cm2 or u should check the impeller size or their should be a propper fittings or casing of gasket is done, so their will be no pressure drop
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Anonymous Poster
#6

Re: Centrifugal Pumps

11/07/2008 9:17 AM

I agree with ALY,

Without specific information we can only give you non-specific answers.

What are you pumping, what is the system and what is the problem?
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2ndthot
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Join Date: Jul 2008
Posts: 29
Good Answers: 1
#7

Re: Centrifugal Pumps

11/12/2008 2:59 AM

the best thing you could do is to change your pump design into a unit capable to do the job, pump unit that are design for that kind of application. Ed Weldon is right. . . . .in some aspect.


try to ask a pump manufacturer if they have a unit that can handle the job.
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Anonymous Poster
#8
In reply to #7

Re: Centrifugal Pumps

11/15/2008 1:33 AM

How to work centrifugalpumps?
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ducon
Guru

Join Date: Dec 2006
Location: Hop around Toronto, New York & Karachi
Posts: 1876
Good Answers: 19
#9
In reply to #8

Re: Centrifugal Pumps

11/15/2008 6:59 AM

Sit on it. That should do.

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 I not only use all the brains that I have, but all that I can borrow. Woodrow Wilson
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Ed Weldon
Guru

Join Date: Oct 2008
Location: I'm outa here
Posts: 1924
Good Answers: 196
#10
In reply to #8

Re: Centrifugal Pumps

11/15/2008 11:10 AM

Fill pump with water. Rotate shaft whichever way pumps the best. Do not stand in front of discharge or you will get wet.

Ed Weldon
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2ndthot
Associate

Join Date: Jul 2008
Posts: 29
Good Answers: 1
#11
In reply to #8

Re: Centrifugal Pumps

11/17/2008 5:02 AM

a standard centrifugal pump (horizontal end suction design) only throw the water away from it. Its sucking power is not that strong, compared to its trowing power, thats why if you could check the performance curve, it always has a positive suction head. There are plenty of centrifugal pump design that is made to this kind of application, made specially for low suction head, sometimes even negative suction head. Increasing the suction head cannot be achieve by modifying the unit.
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SAMSAM
Active Contributor

Join Date: Dec 2008
Posts: 17
#12

Re: Centrifugal Pumps

12/01/2008 3:14 PM

1)Go up with the fluid in the tank - go up with the pressure on the inlet.

2)Go lower with the pump

If above not possible buy a new one but check the NPSHr (pump) on the offer.
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Users who posted comments:

2ndthot (2); Aly Badawy (1); Anonymous Poster (3); ducon (3); Ed Weldon (2); SAMSAM (1)

Previous in Forum: Centripetal Force or Centrifugal Force?   Next in Forum: BASE FRAME

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