Pump Noise Question

[rafadan]

Does my pump seem to be working fine or is this noise and vibration on the gauge indicating a problem? The fluid is thermal oil, the centrifugal pump works at 3000 rpm.

I am suspecting it could be entrained air or limited suction flow.

If it is regarding limited suction flow, will decreasing the discharge valve opening help?
Could impurities in the line cause a noise like this? There is a 0.8mm strainer at the pump inlet but I have noticed smaller particles from the pipe welds etc.
Could it be misaligned coupling?
Does rotating the vane by hand help deaerate the pump? Any suggestions on a way to take out the air out of the pump?

Any other tips or suggestions? Thanks in advance

 

[Strong]

You video does not show the pump or indicate anything about it. The audio is not calibrated for sound level, but it does not sound like Cavitation, so I would not conclude that air is present. The gage needle has slight vibration that might be typical of the way it is mounted. Misalignment coupling: either do a vibration analysis or measure alignment with dial indicators or laser system. If pump is centrifugal type, then reducing flow may reduce sound and vibrations, if new operating point is closer to BEP. Impurities do not cause much, if any, noise; unless that clog strainer and reduce suction pressure. A video camera is not the best tool to use to confirm any of your guesses of machine faults, if any are really present!

Walt

 

[rafadan]

Walt Thank you for the comments. I will check the strainer, align the coupling and reduce the flow to see if helps.

I was thinking it could be air entrainment rather than cavitation as it is the first run.

Can you tell me why the gauge vibrates when it is mounted as such? In the current setup the gauge is right after the pump followed by a check valve.

There is also another gauge right after the oil heater coils, and there is no vibration in that one.

 

[Artisi]

First up, air entrainment and cavitation are 2 seperate animals and are independant of each other, the gauge fluctuation can be blade pass problems or simply a combination of pump speed / installation / pipework, valve placement etc. The video tells us nothing.
Try reducing the flow by throttling the discharge valve, if the noise reduces if could be but not necessarily cavitation.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[electricpete]

is this ...vibration on the gauge indicating a problem?

I did not detect the gage vibrating, but the needle on the gauge is certainly "vibrating" or fluctuating... I assume that's what you're referring to. In that case the gage is simply responding to a fluctuating fluid pressure. There can be a variety of causes of fluctuating pressure, including normal blade pass frequency pulsations mentioned by others. Personally I wouldn't be concerned by seeing a pressure gage fluctuating - at our plant most pressure indicators on discharge of a pump have "snubbers" in-line between the pipe and the gage to dampen the pressure pulsations to protect the gage and make it easier to read. I'm guessing maybe that pipe loop was a (poor?) attempt to do that (I can't think of any other purpose for that loop).



=====================================
(2B)+(2B)' ?

 

[rafadan]

Thank you for the answers.

I am also guessing the loop connection was maybe to dampen the gauge needle vibration by keeping an air layer in between. There is also one loop before a temperature gauge which I don't quite understand. Does the blade pass frequency pulsations mean some kind of natural frequency of the liquid flow caused by the blade movement? Is it normal to see it in a 3000rpm centrifugal pump? I will be at the site in a few days and try to make some adjustments.

 

[electricpete]

Blade pass frequency is the rate at which impeller vanes pass by a given stationary point (number of vanes times rpm). There is some degree of pressure pulsation and vibration inherent in all centrifugal pumps (some more than others, but generally the pulsations associated with centrifugal pumps are not as much as positive displacement pumps).

But thinking about it some more, I don't think the needle would be capable of responding much at a frequency as high as blade pass frequency, which for your 3000rpm motor would be 50hz times number of blades. Even if only 3 blades (it's probably more) that would be 150hz. What I can see in the video I'd guess is 5-10hz.

Maybe it is just fluid turbulence close to the pump discharge creating the needle movement. I'm not much of a fluids guy but I work in a power plant and I'm used to seeing many of our pressure gages moving like that (so it doesn't strike me as unusual). Maybe others can add their comments on what are the common causes of gage needle movement and whether you should be concerned.


=====================================
(2B)+(2B)' ?