KB002001: What is the Purpose of a Gas Ballast Control? - General LC/MS 

The gas ballast control on the E1M18 rough pump for the LC/MSD serves two primary functions; 1. To prevent the condensation of vapors inside the pump. The condensates will contaminate the oil, cause performance to deteriorate and may cause corrosion of the pump mechanism. 2. To allow the oil return function to operate correctly. Note: The gas ballast valve must be opened a MINIMUM of 2.5 turns for gas ballasting and the oil return function to operate correctly. Additional turns will admit more air into the pump, but this is NOT essential, since the pump is effectively ballasted with 1.5 to 2.0 liters/min of nitrogen from the LC/MSD.