Vacuum pump installed in a high position can give better vacuum 1

[lotus7312]

Hi, all,
My boss said that somebody told him that if a water ring vacuum pump was installed in a high position(say, on the roof of the plant), then you can get better vacuum. Did anyone hear about this? Is there any theory or logic behind this?
Thanks

 

[Ti85]

My view would be that the closer the pump is to the tank you're pulling a vaccum on the better. Inserting additional piping will both increase the likelihood of air leaks in the system and there will also be a pressure gradient in the piping, sucking is pumping from the other end, (not exactly but you know what I mean?).

 

[tblaser]

lotus7312

Vacuum inside of the pipe is not affected significantly by changes in elevation. Unless the pump is located higher in attempt to separate liquids, I do not see an advantage.

Is he confusing this system with an ejector system which requires barometric leg(s)?

Did you contact a vacuum pump manufacturer for their view?

 

[quark]

Ti85 is right. It should be as close as possible. I don't find any logic in it. Moreover we faced problems with mist contaminating our products when the pump was above the equipment level.

Regards,

 

[aepp]

Is important the water temperature, this affect your vacuum
if water is hot your vaccum is loss
and water is cool you vacumm is high

 

[RogerH]

Some speculation; could it be so that a low (grade) postion of the pump created a liquid leg , e.g. if there is a low point in the suction-side piping and this occasional liquid accumulation is giving an fluctuating vacuum. By placing the pump high this wont happen and hence the vacuum is "better" (i.e meaning stable)

 

[hacksaw]

high or low is not critical, but free draining pipe is

 

[roaling]

In my opinion, the pump installation at high position is better to avoid any possible liquid carry-over and not to get an higher vacuum.

 

[groovy]

Liquid carry-over is normally avoided by installing a small vessel in the vacuum line between the main vessel and the vacuum pump. In this way any liquid which is carried over drops in that vessel instead of going in the vacuum pump. In my experience the water temperature has some effect on the vacuum achieved, whereas the position does not. Position is important in case of ejectors having barometric legs.

 

[hspl]

I agree to friends saying that height has no role to play in vacuum formation and the pump should be as close to the vessel as possible for better evacuation. water temperture should be as low a practically possible for achieving a vacuum close to 710 mm of Hg. If you need higher vacuum try vacuum boosters in addition to the water ring vacuum pump.

 

[bewdley]

I have always followed the rule of thumb of using water at a temperature 3 deg C minimum below saturation temperature at the suction pressure. This does not allow water recycle, though. Moreover, as the pressure drop in suction line is an important figure (just calculate the gas velocity and you will probably be amazed), I only use full bore ball valves and, if not absolutely necessary, avoid check valves on suction.
For the same reason, it is also good practice to locate the vacuum pump as close as possible to the vessel to evacuate - this explains the advice to locate in a high position, as usually this evssel is a condenser or otherwise requires a barometric leg for discharge, so it is normally high.
Last - don' be scroogy, use a big pipe at least suction side.