Vacuum gas ballast valve

[glenn1340]

Hi Guys,
I`ve noticed a few posts asking what a gas ballast valve on a vacuum pump is for. I was in the workshop the other day rebuilding a two stage Edwards vacuum pump and looking at the manual I found this information:

"In a pump stored with the same oil for a long time condensed vapours may contaminate the oil bath and affect performance. This also the case after pumping vapours and when the oil appears cloudy in the sight glass.
-Run the pump, with the inlet valve shut.
-Open the ballast valve and allow the pump to run for 1/2 to 1 hour or longer if the oil remains cloudy. This operation accelerates the temperature ise of the pump while eliminating residual vapours present in the oil bath.

To pump with condensable products it is neccesary to operate with a hot pump.
For this run the pump with the inlet valve shut for 1/2 hour with the gas ballast valve open or 1 hour with the gas ballast closed. When the oil bath is hot the condensation of vapours in the pump is reduced or prevented.

The pump`s capacity to eleminate condensable vapours is related to their type, the pump temperature and the quantity of air introduced by the gas ballast. Thus, for higher vapour levels in a system a single stage pump is more suitable.

When condensable vapours are being pumped, gas is compressed beyond its saturated vapour pressure in the compression phase, ie towards exhaust side of the pump, and can condense impairing performance.

The gas ballast valve is used to inject air inot the last stage of the pump during the "compression" phase so that the partial pressure of the pumped gas (this would be air or nitrogen in a refrigeration system. My words) is less than its saturated vapour pressure at the temperature of the pump. Condensation is, therefore, impossible if this limit is not reached. The maximum admissible vapour pressure is obtained at pump inlet for this value.

The saturated vapour pressure of a body is higher when the system is hot than when cold; therefore the pump must be reach operating temperature before pumping consable vapours."

A word of caution, constant running the pump with the gas ballast valve open can cause significant oil mist from the exhaust it`s advisable to check the oil level often.

I hope this all makes sense.
Glenn

[db133]

Hi

I trying to find information on running an Edwards ED35 Speedivac pump.

Oil change what oil etc.

Any information will be most apreciated.

In any event kind regards.

[Grizzly]

Vacuum pump oil would be advantageous, although if out in the field and without the correct grade.
I have gotten away with fridge grade oil.
After all it is to provide a viscous seal between the vane tips and the chamber metal surface.
As to when to change?
The colour of the oil is always an indication, however it never harms to change the oil.
If in doubt change it it's not going to harm the pump!
How long you intend to leave the pump running is also a deciding factor.
IE. If you have a large system with the pump running overnight then it is always sensible to change the oil first.

Glen thanks for a good post.
Cheers Grizzly

[db133]

OK thanks, we all have to start some where, still looking for the Edwards ED 35 Running Instructions. As I need to know the details, wot goes where and how much, that sort of thing. It might only want TLC and I do not want to **** it up.

Ref the oil for an ED35 "Vacuum pump oil would be advantageous" Is it all the same ? Sorry if its a daft question but I have only just found out there is such a thing as "vacuum pump oil". Found the Gas Ballast knob and a level glass with what looks like an oil drain screw below it and the oil nut on top.............

[db133]

Found the ES&ED Series Maintenance Manual but it excludes the Operation and Routine Maintenance as its in the Working Instructions.........So now I know I am looking for the "Working Instructions" for the Edwards ED 35 Speedivac..........Google ?