Vacuum control valves, unlike vacuum isolation valves whose function is limited to full opening and closing, allow control of volume flows. This is usually done by narrowing or widening the valve passage. The control range varies depending on the design principle of the control valve. This is also referred to as the available conductance spectrum. Valves with a very large conductance spectrum generally allow finer volume control than valves with a small conductance spectrum. However, the design principle and the type of drive are also decisive for the fineness and precision of the valve control. Vacuum control valves are predominantly electrically driven, since the electric drive usually allows very fine and fast position changes of the valve plate. Both are crucial for precise control. In addition to electrically driven control valves, however, there are also pneumatic solutions that e.g. move to mechanically predefined control positions, or manual solutions. Vacuum control valves are also available as pure control valves without an isolation function, i.e. they never seal completely and always allow a minimum residual volume flow, or as control and isolation valves that also offer complete interruption of the volume flow.
Vacuum control valves are available in very different designs, as control requirements for vacuum systems can vary greatly. The following criteria are therefore decisive when selecting a vacuum control valve:
- The level of the maximum differential pressure at which the valve is to control. This is not necessarily the maximum differential pressure that the valve can withstand when closed, if it also has an isolation function.
- The size of the required conductance spectrum, the control range.
- The size of the flow rate
- The speed with which changes in the volume flow are to be carried out
- The resistance to by-products in the volume flow or to aggressive media in general.
- The sensitivity to flow changes e.g. turbulence caused by the control process.
- The sensitivity to particles that may be emitted through the valve.
- The ambient temperatures at which the valve is to be used and at which it is to control.
- The type of controllability as linear flow change or dynamic change, where the control speed can be controlled independently of the position of the valve plate in a so-called control profile.