Gas Ballast Valve, What is it for?
All 2-stage pumps of model VPDx and VPEx made by VIOT are shipped and contain a gas ballast valve. This is viewed as a brass adjustable knob (thumb operated) on top middle of the pump. Often in evacuation work, the user will get water, or solvent vapor or other condensible contaminants as part of the gas stream and trapped in the vacuum chamber/oil. These contaminants come over because they have turned into gas from a liquid under vacuum. They then travel to the pump and turn back to a liquid and mixed with in the pump oil. All liquid chemicals have a physical character 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
