Limit Switch usage on SDV and control valve 1

[Ulon]

Hi all,

Motor actuated control valve shall have limit switch, but for pneumatic and hydraulic usually all SDV will have limit switch but not necessarily for Control Valve?

Any comments?

Thanks

 

[hacksaw]

the motor actuator requires it to control the motor, the valve does not. beyond that it depends on you control requirements

 

[JLSeagull]

Consider the different switch functions.

Limit Switch
I use the term limit switch as the torque related switch that removes power from the electric motor for a motor operated valve.

Position Switch
For both electric motor and pneumatic on/off valve applications, the open and closed position switch contacts permit displaying the valve position on the HMI and to include the position status in the control logic if desired.

Position Transmitter
Some critical throttling control valves include a transmitter that provides the feedback of the actual valve position instead of using the output a.k.a. implied valve position. Transmitters are becoming more common in on/off valve applications too.

 

[JLSeagull]

Also, analog + HART outputs are increasing in use for shutdown valve operation. The diagnostics are improved using an elevated zero (4 mA) for the off status (close command for a shutdown valve) as compared to zero volts for a 24 Vdc solenoid.