In standard valves, when the valve is given a command to open to a certain point, there is no feedback to verify that the valve has opened to that position. With a valve positioner, the command is given and the valve positioner reads the opening, verifying the position and readjusting until it gets it to the exact position needed. This allows for great precision in the valve adjustment.
There are many applications for a valve positioner. Valve positioners are often used in vehicles such as cars, trucks, airplanes, trains, rockets and space vehicles. Valve positioners are also commonly used in the medical, pharmaceutical and food industries.
A valve positioner can be used in either linear or rotary valves. There are four basic valve positioner types: pneumatic, electronic, electro-pheumatic and digital. To verify the safety and accuracy of a valve positioner, it should have an Underwriters Laboratory (UL) or Canadian Standards Association (CSA) stamp of approval.
Pneumatic valve postioners communicate with air. Electric valve positioners use electric signals; single or three-phase AC or DC current is used. Electro-pneumatic valve positioners take an electric signal and convert it to a pneumatic (air) signal. Digital valve actuators use a microprocessor to monitor the valve accurately.