Liquid Ring Pump Vacuum Loss

The warmer the water the more vapor is generated thus compensating the vacuum since part of volume is filled with water vapor !

Water has a partial pressure that varies from a few MM at zero C to 760 MM at 100C.

At 100 C the pump totally fails. At temperatures rise you get a progressive failure to total. This is what nick name says in other words.

By looking at your question it seems that first culprit is rise in temperature of the sealing liquid. But please understand that not only seal liquid, but there are other factor's which may lead to reduction in pump capacity.

First of all; note those liquid ring vacuum pumps are versatile machines in "wet load" (condensable gases) application.

Also note that sealing liquid is absorbing the heat of compression, friction & condensation.

The capacity of the pump is greatly influenced by vapour pressure of the sealing liquid, and the vapour pressure will vary with the change of sealing liquid temperature. When sealing liquid temperature rises, vapour pressure also rises, thereby reducing pumping volume. Please refer following chart.

Lets take the example of the pump running at seal liquid temperature of 15°C at 40 Torr. If there is raise of seal fluid temperature of 5°C the capacity of the pump drops down to 20%.

So increase in seal water temperature is not good for the pump capacity.

Now you are saying that your pump capacity is dropping with increase in seal water temperature. That means something is going wrong in the system & not only in the pump.

There could be some reasons (as listed below) for the same;

Ø Inadequate seal water flow (due to low flow the heat absorption capacity is not enough & in every cycle it is getting heated & may be is vaporising.

Ø Excessive sealing liquid leakage from the packing / seal. (loss of water will increase the temperature)

Ø Recirculation heat exchanger choke.

Ø Recirculation pump performance is in adequate.

Ø System leaks - Sources of leaks can include open drain valves, blown gaskets, loose flanges, poorly packed valves, inadequate barometric drop legs on separator, broken pipes etc. Higher leakage will result in lower vacuum.

Ø Variation in pump rpm - If rpm is low, pump will run at a lower capacity. Check motor and V-belt.

You have to check following;

Ø Pump performance like pressure, temperature, pump seal tightness, and in case of packing replace it with seal.

Ø Check the pump operating point; if the operating point has shifted to the left may be you have to check for the HE choke.

Ø Check for the seal water adequate supply.

Ø Low seal water flow could be due to a plugged strainer or partially closed valve in the recirculation line.

Ø Check in the system whether hot condensable gases along with the non condensable gases are introduced in the system.

I hope after complete check of the system as above there should not be any problem