3.6.6 Gas dosing valves and gas control valves
Gas dosing valves are used for the inlet of defined gas flows into a vacuum system, for example, to maintain or set a certain pressure. They often work according to the principle of a needle valve. By turning a spindle, a gap is released and this opening and length provide the flow conductance. The gas flow is dependent on the spindle revolutions and is represented as a characteristic curve. The valve position can be read from a scale and set reproducibly.
Gas control valves are motor-controllable dosing or proportional valves, where the size of the valve opening continuously increases with the applied coil current, all the way up to the maximum opening. The volume flow associated with the coil current is illustrated in the characteristic curve. Control valves are operated by control units or are directly controlled by external controllers. They are used in automated processes for pressure or flow control.
For very low flow rates under UHV conditions, e. g. for mass spectrometer applications, there are bakeable all-metal gas dosing and gas control valves that seal with a ceramic plate against a metal seat.
Figure 3.24: UHV all-metal gas dosing valve