Noisy Vacuum Pump 1

[finite]

I am running some new vacuum pumps that we have just purchased. All the pumps are the liquid ring type. The pump is quite to a pressure of approx 80 Kpa(negative). As soon as I close the suction port to reach a pressure of 88 to 92 Kpa(neagative) the pump becomes noisy. I have checked that I have the correct coolingf fluuid flow rate, as well as the fact that the cooling fluid in the supply tank remains at the centre line of the shaft.
Please any suggestions

Finite

 

[fredb]

Hello,

Noisy liquid ring vacuum pumps can be caused by:

1. Coupling misalignment
2. High seal water flow
3. High discharge pressure
4. Improperly anchored pump
5. Bearing failure
6. Water filled casing during start-up
7. Lack of air flow to the pump

 

[mbelaidy]

You should have silencer because it is a common practice in vaccum pumps.

 

[25362]

Techniques for noise control include:

1. Modification of the basic pump design and/or operating conditions to minimize the generation of acoustic energy.

2. Interruption of the transmission of noise, whether borne by the structure (use flexible couplings and/or flexible resilient supports), liquid (use pulsation acoustic filters) or air (use absorption materials on the pump enclosure).

 

[quark]

I agree with fredb about lack of air flow to your problem. Becoming noisy at closed suction condition or near full (available) vacuum condition is a characteristic of liquid ring pumps. At very low pressures as there is no inrush of air water evaporates and cavitation occurs. As these pumps are progressive cavity type and compression occurs downstream bubbles break creating noise. Not to worry much about it. Just bleed some air through bleed valve if the noise is unbearable.

Silencers are installed at discharge and these things will not help much incase of your problem.

 

[alexsschen]

Cavitation is definitely the reason for the noise. Bleeding of air will increase the suction pressure but will be a straight foward / good solution only if the final achieved suction pressure is lower than the required suction pressure.

Otherwise, a cooler seal water / liquid supply is needed. Vapor pressure of the water/liquid at that particular pressure and temperature is the theoritical achievable vacuum / pressure.

 

[finite]

Thanks for all the answers. I was told yesterday that the manufacturer had welded ribs on the ensd of the blades. Now the ribs have been removed the pump is running quietly
Finite

 

[joken]

I have oil cooled liquid ring pumps that incorporate a suction relief to prevent this problem. The pumps have a 10 min delay off and this sometime creates vacuum below setpoint which would result in noise. A very small amount of air enters this valve and it works well. If only I could keep the seals from leaking.. Joken