A control valve is fitted with an actuator & electronic positioner. The valve fails closed on loss of air. The positioner is calibrated 4ma open, 20 ma closed. What position would you find the valve with loss of ma signal?
A) Fully open
B) Fully closed
C) As was before loss of signal
D) Depends on flow

 

When a control valve is fitted with a spring-to-close actuator, it is designed to fail closed if air supply is lost. This means that without air pressure, the valve naturally moves to the closed position.


In this setup, the electronic positioner is calibrated such that 4 mA fully opens the valve and 20 mA fully closes it. The positioner converts the electrical signal into air pressure to control the actuator. When the signal is lost, the positioner can no longer maintain control.


Since the valve is spring-to-close, loss of signal leads to loss of air to the actuator, causing the valve to move to its fail-safe position: fully closed. For a related example of actuator control in electronics, see this https://www.pcbway.com/project/shareproject/Flex_PCB_based_Actuator_fd1bc013.html

 

Thanks for explaining so clearly—that’s what I was thinking too
I have an exam coming up soon, and I wish I could get your help with a couple of questions so I can get a good explanation

 

The question does not have any detail about the action of the positioner on signal failure. Loss of signal does not necessarily mean loss of air to the actuator. As 0mA is less than 4mA my answer would be Fully Open.

 

I am confused between full open and full close even AI they get confused