glenn1340
26-02-2011, 06:24 PM
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
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