4 replies to this topic

[parsomash]

Hello All,

 

Here is the issue we got: we have a centrifugal pump needs to pump 15000 gpm from a cooling pond, the pump exceeds its volume rate and head which is 100 ft, but the problem is, on suction side you can hear horrible noise of cavitation. what  suprised me during our manometer test(which proved our calculation for NPSH and result is acceptable) was when accidently we left a pressure gauge valve connected to the suction line open, at the sudden pump worked smoothly with no noise. so we thought this is because of turbulance in the suction so that sucked air help to break the turbulance steam. then we put a vortex breaker there( a vertical and a horizontal in front of each other like a plus). now the pump is working fine with lower rate like 50% capacity but when the demand go higher pump goes nut and again horrible noise. please le me know what do you think ? what would be the reason? what should I do to eliminate the cause of problem?

for now, we think it would help if we increase size of suction pipe to 30 or 36"( now is 24") but the issue then would be sump distance to the inlet. any recommendation is highly appreciated.

the attachment may help to understand the subject better.

Attached Files

•  PUMP BLOCK scketch.pdf   19.87KB   34 downloads

[mansari]

In my opinion, suction side velocity is too high at your peak demand. 24" pipe with 15,000 GPM means a velocity over 11 ft/s, a velocity never recommended for suction piping. Recomendation is < 1 m /s or about 3 ft/s, therefore the appropriate suction line size for the given peak flow comes out to be 42". This could be the reason your pump operates smoothly at low loads.

[breizh]

Hi , 

 

Consider these 2 documents to support your query :

 

As stated in the previous reply  : Velocity far too high , I will add possibility for air to enter at the suction due to vortex or solubility .

 

Hope this helps

 

Breizh

Edited by breizh, 26 June 2013 - 06:06 AM.

[prengr]

I think you should be better changing your suction line size.

I roughly calculated velocity and pressure drop for 24" pipe. The result is that velocity is 3.4 m/s and pressure drop is 0.12 kg/cm2 / 100m. As you can see, velocity is slightly high for pump suction line. This can make some problem like your case. Therefore, I recommend increasing the line size whose velocity is to meet under 1.8 or 2 m/s.

[parsomash]

Thanks for all your replies.

 

Yes, I agree with you about bigger pipe size but what I am not sure or let's say I am suprised by sending air into suction side (there is a connection for pressure guage on the horiziontal run) that cure the issue , no noise no vibratiion. So, you think that is all about reforming the turbulance by sucked air?

Edited by parsomash, 26 June 2013 - 11:36 AM.