- externally controlled valves
- electro-pneumatic valves
- air-controlled valves
The raising of the sealing element is done with compressed air, directly via an externally controlled actuator. In single-acting actuators there is a pressure spring for the return to the rest position, taking away the control air.
We distinguish between
- externally controlled poppet valves
- externally controlled coaxial valves.
Externally controlled poppet valves:
The standard functions are: 'Closed with spring force and medium flow' or 'Closed with spring force against medium flow'.
In liquid-carrying pipelines, valves that close 'against the medium flow' are used for shut-off in order to reduce the water hammer.
The valves are controlled by a pilot valve, typically 3/2-way or 5/2-way.
Pilot-operated valves are suitable for controlling gaseous, highly viscous, conditionally contaminated and aggressive media. The drive (control) chamber is separated from the main medium.
Coaxial valves, externally controlled:
The switching process with this type of control takes place almost without friction and without differential pressure. This design allows any flow direction. NO- with spring force open is possible as well as the standard function NC- with spring force closed. The control air connection is realised by a Namur interface.
The following applies to externally controlled valves:
- Control pressure 3-8 bar is required
- Control medium preferably air
- fast opening and closing time with high repeat accuracy.
- Any installation position