Vibration of pumps

[B.L.Smith]

Dear Friends,

I'm not a Equipment man. But I'm piping stress analysis.
I have a question:
Have you ever seen vibration of pumps? what is the reason of this vibration? have you ever seen use of expansion joint at suction or discharge of the pump for damping this vibration?

 

[1gibson]

Rotating equipment will vibrate, if it is worn out or not operated as designed then it will vibrate more. A joint that "loosens" the connection will probably increase pump vibration, but may reduce piping vibration. Does that really solve your problem?

Unless it is a natural frequency problem, that wouldn't help.

P.S. thank you for saying "damping" and not "dampening." Getting the vibrations wet would not help.

 

[bimr]

If the pump was not designed, sized, or installed correctly, you may see increased vibration.

 

[bimr]

Examples:

Pump should have a concrete foundation which is 2-3 times the mass of the pump. If not, there may an increase in vibrations.

A pump that is operated off the best efficiency point will exhibit more vibrations.

 

[JJPellin]

The most common sources of vibration in a pump would be imbalance, misalignment, bearing failure, cavitation, pipe strain, foundation design, internal rub, structural resonance and earth quake.

Johnny Pellin

 

[stanier]

Add to that poor pump selection where the operating point is not close to BEP.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[QualityTime]

Putting expansion joints at the suction and discharge of the pump is not a good idea. You are creating unbalanced forces which will expand or contract the expansion joint. Your pump can go for a walk if the forces are large enough. The best thing to do is to to have flanged fittings/welded pipe.

Long ago I was asked to look at a 4000 HP pump that had a working pressure of around at 240 psi. I can't remember the capacity of the pump but I beleive the pressure thrust was around 120,000 lbs. Then engineer had a restrained victaulic coupling between the check valve and the butterfly valve. The play in the restrained coupling allowed the pump went for a walk when the pump was started up the first time. I advised the Owner that tie rods should be installed between the butterfly valve and the check valve to make the joint rigid (same as a flanged joint). It worked. The engineer did not know the subtilties between a restrained joint and a flanged joint.

The same engineering company did the same thing on a 72" diameter line in a water plant. The pressure thrust was around 700,000 lbs. The restrained couplings engaged under pressure as it should. The movement however cracked the shoulder on the concrete pipe supports. All of the couplings were removed and replaced by welded joints. I advised the Owner well before the piping was installed that this would havppen. There have been a lot of catrostrophic coupling failures in the US. The engineer shoould have just specified welded joints.

Pump vibration can be caused by a lot of things. Most were mentioned above. The other thing that can cause vibration is if vortexes or air is being sucked into the pump suction