Regulation of Vacuum on Liquid Ring Pumps

Let in air.

Thanks just need to work out how as the company did not supply not supply any pressure control valves to regulate pressure in our tank, and centrifugal pumps struggle to discharge properly. any suggestions on the control of letting in air???

Use a vacuum relief valve. The pump supplier may be able to provide it.

I've used LR vacuum pumps where a vacuum relief valve was included as standard, to avoid cavitation if the pump operates against a closed suction (maybe not required by all LR pumps). In one case we specified 80mbar (at a certain flow) and a vacuum relief valve opening at 200mbar (their standard) had been fitted. We had to get them to come and change it, or perhaps it was possible to adjust it, I can't remember.

Cheers.......Codey

If the water used in the pump is at 60C you the vacuum will be automatically controlled to about 200 mBar. A simple flow control valve (globe valve may be enough if there is active vapour generation in the system). A controlled air leak using an air inlet with a flow control valve is one more option. Bioramani

Use a gas flow controlled with a control pressure valve with a pressure transmiter if you need tight control. Be sure to properly estimate the control valve Cv. If you have a small system, and you don't need high precision, you can tray with a globe type valve, 1/2" or 3/4". Use air if your system is friendly and there is no risk of explosion or risky reactions.

Most vacuum systems using Liquid Ring Pumps should have 'by-pass-valve' between discharge to suction. The normal practice is to keep open this valve during starting and slowly closing this as the vacuum pump stabilises. This helps in effecting vacuum gradually without shocks at suction side.

If you have such a by-pass-valve, adjusting this valve would help in achieving the desired vacuum.

Normally such valves use to be 'gate valve' and not suitable for controlling purpose. You will be surprised that, opening this valve by 5 to 8% will totally unload the compressor. So you may have to have a globe valve in parallel to this 'start-up by pass valve'.

Most vacuum systems using Liquid Ring Pumps should have 'by-pass-valve' between discharge to suction. The normal practice is to keep open this valve during starting and slowly closing this as the vacuum pump stabilises. This helps in effecting vacuum gradually without shocks at suction side.

If you have such a by-pass-valve, adjusting this valve would help in achieving the desired vacuum.

Normally such valves use to be 'gate valve' and not suitable for controlling purpose. You will be surprised that, opening this valve by 5 to 8% will totally unload the compressor. So you may have to have a globe valve in parallel to this 'start-up by pass valve'.