VS4 pump having high vibration possibly due to wrong bush clearances

[Hamza1988]

Hi, a VS4 type vertical pump is having high vibration though the pump was recently overhauled. The pump bushes were replaced during the overhaul and the sleeve-bush clearance was 0.28 mm. The issue was that the pump manufacturer did not provide any design range for the bush clearances therefore we set between 0.25 - 0.30 mm. The sleeve diameter is 40 mm.
Soon after the overhaul, the pump was run and the horizontal value of vibration seems to be on the higher side at the motor D.E side. The motor bearings were also replaced.

What do you guys think could be the issue? Also, API 610 does not provide the recommended values for the bush clearances in a VS4 pumps. Is there an authentic journal or standard that can be followed to set the bush clearances in vertical pumps.

Thanks.

 

[LittleInch]

What's the coupling design?

Assume it was all aligned OK in static condition?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Strong]

Was the clearance when pump was removed prior to overhaul 0.28 mm? Were the same high vibrations present then? What wear was indicated on the shaft journal and bushing/bearing?

Walt

 

[JS_]

I built pumps for over nine years.

Usually default to Mark's handbook to figure clearances...

I'm assuming Bronze bushing and Stainless Steel sleeves.

If pumping water, these are the clearances that I used for shafting turning 1800 rpm .010" - .015" or roughly .25mm to .38mm


What type of impeller? open? closed?



I have seen these problems with short coupled pumps:

wrong rotation which causes the threaded couplings to unscrew. This causes a side loading and whip action of shafting.

misalignment of motor to shafting

incorrect balance of impeller or impellers

shafting incorrectly straightened or not straightened, IF shaft is one piece and turned it may have relieved internal stresses and is bent.

wrong clearances

and my favorite one: severe Cavitation blamed as a balance issue......

 

[JJPellin]

For that shaft size, I would specify the clearance as 0.006 inch to 0.009 inch on the diameter for a bronze bushing over a stainless steel shaft or sleeve. I am assuming 3600 rpm or 1800 rpm. Your bushing clearance may be a little bit on the high side. I would add to the excellent list that JS provided:

Shaft run-out caused by a threaded coupler where the shaft ends but up against one another
A bent shaft caused by buckling after running at excessively high flow rate, resulting in upthrust.

It would be easier for us to make good suggestions if you provided the number of stages, the bushing material, the sleeve material, the rotational speed and the fluid being pumped.

Johnny Pellin

 

[CouplingGuru]

In addition to checking alignment at the coupling, also check run-outs on coupling hub to to shaft. On some occasions you could have a severely off center bore in your coupling. That could add significant vibration depending on coupling style and size.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[Hamza1988]

Thanks guys,

The coupling is a jaw coupling.

The pump was initially overhauled due to the same reason, high vibrations. When our vibration analyst performed the analysis, he found high bush clearances to be the reason. We removed the pump and replaced the bushings with new ones as a lot of scoring was observed in the bushings though the sleeve was found to be good and smooth. The bushings are not bronze but polymer based. The clearance values of the old bushings could not be measured accurately due to heavy scoring but these were within the range of 0.30 to 0.35.

We also checked the runout of all the shaft and a maximum value of 0.05 mm was found.

Any imbalance in the impeller was not checked though.