To ensure that the full valve differential pressure can be accepted, it is important to adjust the positioner zero setting so that no air pressure opposes the spring force when the valve is seated. Figure 6.6.13 shows a typical positioner. Commonly, this would be known as a P to P positioner since it takes a pneumatic control signal (P) from the control system and provides a resultant pneumatic control output signal (P) to move the actuator.

Both pneumatics and hydraulics are applications of...


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