Vibration in Suction piping

[Mechya]

Hi, My question is about the vibration that is experienced in the suction piping of a single stage centrifugal pump in a chilled water application for human comfort.
The piping arrangement is like this; suction has positive pressure with a air separator and a strainer installed just before the suction point, whenever the pump is in operation, the whole piping from the strainer to the pump suction point vibrates. Can anybody advice me on the causes.
Thanks..

 

[DesignerMike]

How close is the strainer to the suction of the pump?

What is the velocity through the line? (or give line size and gpm)

Is the strainer sized correctly.
Did you take the strainer out and test without screen to see if that was the cause?

What type of strainer?

I doubt that I will have answer, but these are questions that would help us help you.

 

[pennpiper]

I have seen this before. In the case I saw both the suction piping and discharge piping were vibrating. The client claimed that we (our company) were guilty of improper design. After we did a complete study we found that the fault was theirs. The level controller on the suction source tank had failed and the level was at the very bottom. The pump was cavatating. That was the cause of the vibration.
Therefore I say check your suction source.

 

[mfi2000]

Does the pump vibrate? Is it aligned properly. A lot of places use vibration eliminators on the suction and discharge piping due to turbulence in the system which cannot be cured. Are there any other pumps which do this?

 

[proinwv2]

I agree with the possibility of cavitation. Have you actually measured the suction pressure?

Paul Ostand

http://www.ostand.com

 

[imok2]

may want to read this:

http://www.mcnallyinstitute.com/11-html/11-12.html

 

[TBP]

I doubt very much that you can get cavitation on a chilled water pump. The temperatures are typically 45*F supply to the system, and 55*F return to the chiller. The chilled water circ pumps are typically (or should be...) very low head, because the piping system is a loop. Every GPM that leaves the pump discharge returns to the suction. Even in tall buildings, the loop is like a ferris wheel - the weight going up is equal the weight coming down - so relatively little power is required. Velocities are kept low, or else there will be noise complaints from occupants.

I'd check alignment, and possibly that the impeller was properly balanced at the factory.

 

[cvg]

if your strainer is plugged, you could get low pressure and cavitation... Check the strainer

 

[TBP]

Does someone have experiece with a chilled water circ pump actually cavitating? I don't mean theoretically - I mean actually seen it in the field - steam bubbles forming in the suction of a chilled water circ pump and then collapsing the higher pressure areas of one of these low head pumps. I really don't think it's possible, but I've been wrong before. You'd get dissolved air popping out of solution long before cavitation became an issue. I think that if anything, the pump would become air-bound, rather than cavitated. You'd also have complaints from building occupants regarding lack of AC if the flow was restricted to any degree by something like a blocked strainer. Most hot water heating/chilled water pump installations I've seen, have a pressure gauge installed across the circ pumps. In any event, strainers are easily checked. I don't think it's mentioned how old the installation is. If it's a brand new system, I suppose there could be contruction debris in the lines. If it's a system that's been in service for a few years, and there's so much corrosion & fouling that a strainer could be blocked - wow - then there are FAR greater problems than just a vibrating pump.

 

[Mechya]

Hi, Thank u all very much for the advices, I check the strainer and found partially blocked; actually,this is a an old installation and a week before some work was done near the strainer, welding and little hammering caused the scale and corrosion particles inside the piping to dissociate and block the strainer...

Thanks to you all once again...