China manufacturer of magnetic ballasts for metal halide flood lights & hps flood lights

Means through which air or another non-condensing gas is admitted into a vacuum pump are referred to as gas ballast. If the pump is displacing vapor that would condense in the pump at the corresponding temperatures without gas ballast, the gas ballast enables the outlet valve to open before the vapor condenses, and the vapor is discharged together with the ballast gas. Both atmospheric air as well as selected inert or process gases are used as ballast gas. The use of the gas ballast increases the attainable base pressure of a vacuum pump slightly. Consequently, for gas ballast vacuum pumps the base pressure is specified both with and without gas ballast.

The vacuum pumps are shipped and contain a feature known as the gas ballast valve. This is viewed as a black adjustable knob on top of the pump.

Often in vacuum work, the user will get water vapor, solvent vapor or other bad contaminants as part of the gas stream being evacuated from the vacuum chamber. These contaminants come over because they have turned into a gas molecule from a liquid molecule under "X" vacuum pressure and the pump pumped them out of the system. They then travel to the pump and turn back from a gas to a liquid in the pump oil.

All liquid chemicals have a value known as vapor pressure. This vapor pressure is a function of physical chemistry law. The basic formulae is PV=nRT. I could get into an explanation more detailed here, but suffice to say that as a result of this formula, water will boil at room temperature when a vacuum pressure of roughly 29.5" mercury vacuum is achieved. When water boils it is turning from a liquid into a gas. All chemicals have this feature, just at varying temperatures and pressures based on their molecular construction.