Cavitation in closed loop pumping system 1

[Aptx4869]

Dears

Kindly, I want to hear from you regarding this topic. The system is closed cooling system.

I believe it is difficult to attribute the sound you hear from centrifugal pump to be a cavitation especially if the discharge pressure is normal.

The last time we had a problem with this system is that the the suction valve was fully closed (we thought it was open).The discharge pressure was normal and there is no sound from the pump. This happens because the suction valve is like a discharge valve that is far away from pump (closed loop). So if the suction valve is closed, there will be no flow and liquid will just recirculate in the pump casing.

If there is a strainer upstream of the pump that is nearly clogged, it may cause cavitation, but only if the discharge pressure is low. then you can say there is a possibility of cavitation.

Now, one of our pumps has a sound (difficult to tell what it is), but since the discharge pressure reads normal, I would say maybe the sound is from the pump bearing.

Please I will be happy to hear from you to know If I have some misconceptions here. Please comment

 

[Artisi]

Fit a compound gauge on the inlet, removes all doubt of what is happening on the inlet side, also can you measure flowrate through the pump and measure power draw? .

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.)

 

[SandCounter]

Do you have a head tank?

I used to count sand. Now I don't count at all.

 

[Aptx4869]

SandCounter

We have an expansion tank that is on top of the system.

 

[Aptx4869]

Artisi

We have a pressure gauge between the inlet of the pump and the suction strainer. How can I use it to my benefit ? What if the inlet pressure gauge indicates 5 psig. (It seems to me the cavitation is difficult to happen in this situation). The liquid is demineralized water mixed with Hydrex 2510S for treatment. The liquid temperature is 100 F.

You mean when cavitation happens, that means there will be less current drawn by the motor ? Again we had a case where the suction valve was fully closed and if you have measured the current in that situation you will notice small current draw, but that does't necessarily mean you will have cavitation

The discharge of the pump will go to various systems for cooling. Each system has a flow meter. I imagine If there is a cavitation, the flow rate will be low, but again we have a suction pressure of 5 Psig ? the temperature of inlet water to the pump is 100 F

 

[Artisi]

If the inlet was restricted by a closed valve, you had 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.)

 

[Aptx4869]

Dear Artisi

I have witnessed the case where the suction valve was fully closed (I am talking about closed loop pumping system)and there was no abnormal sound in the pump. the fluid was just recirculating in the pump casing with zero flow

 

[LittleInch]

For most pumps if the inlet pressure into the pump is more than 0 barg/psig, then cavitation is unlikely.

You can get essentially blocked outlet and recirculation within the pump with high discharge pressure, but no cavitation.

For no flow situations your electrical power input is reduced.

You are correct in that cavitation is not always the cause of noise in a pump. If you've abused this pump as much as you say you have ( closed valves, re-circulation, blocked filter etc etc,) then I'm not surprised the bearings or other part of the pump is making noise.

Did you also forget to fill the oil bottle on the bearings for some time or perhaps turn off the bearing cooling water?? Was the header tank always filled up or at the right pressure?

You are drip feeding information here and it's getting a bit annoying. Please give us all the relevant information and ask a sensible question.

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

 

[lilliput1]

Calculate the available NPSH and compare it with the pump operating required minimum NPSH. The pump will cavitate if the available NPSH is less than the minimum required.