A positioner is used to adjust the position of a linear or rotary valve actuator, in response to a signal received from a controller. They are very precise and thus are frequently used in control applications to increase response speeds and allow for quicker loading and venting. A positioner is mechanically connected to the stem or shaft of a valve, allowing a comparison of its actual position with the position programmed by the controller. If this position is different, the valve positioner conveys necessary feedback to the controller, which then moves the actuator until it reaches the correct position.
What are Positioners?
Valve positioners are available in several different types:
- Pneumatic positioners operate on pneumatic signals to supply the correct amount of air pressure to the valve actuator. They are inherently safe and can supply large amounts of force to operate the valve.
- Electric positioners perform the same function, but operate on electricity to provide the input signal. They can be supplied with DC voltage, or AC in either single or three-phase current.
- Electro-pneumatic positioners are self-explanatory, using a mixed operating system of both electricity and air.
- Digital or smart positioners operate by means of a microprocessor, which positions the valve actuator, and at the same time monitors and records the functional data. They operate in a very similar fashion to an analogue positioner, but use a digital signal conversion rather than an electronic one. Smart positioners are extremely accurate, incorporate online diagnostics, and use less air than their analogue equivalents.