How to Solve On-Off Valve Problems?

In this article we will discuss about problems we face in On-Off valve and their troubleshooting steps to solve the problem.

On-Off Valve Problems

Below mentioned steps will help you to solve the problems being faced in an On-Off valve

• Physically check all the components/accessories of the On-Off valve. No leakage or no physical damage should be present. If any leakages are found, then attend them after taking proper work permit as well as other precautions. If any accessory is found damaged, then replace the accessory.
• The air supply pressure to the On-Off valve’s actuator should be as per the value mentioned in the datasheet. Air pressure can also be found on the actuator’s name plate. Do not set air pressure more or less than air pressure mentioned in the datasheet. This will damage the actuator or make valve movement sluggish respectively.
• Also check all intermediate valves for air isolation. All should be open.
• Some valves in the air supply circuit are present to directly open or close the ON-OFF valve. They are called bypass valves which manually operate the ON-OFF valve. Ensure that these valves are closed if present in the circuit.
• If gearbox is present, then ensure that the gearbox is in auto mode.
• Try operating the ON-OFF valve through the gearbox’s handwheel. If found hard during operation, either gearbox is having issue or the body is stuck. Check for the issue with Mechanical team.
• Operate the On-Of valve from the PLC or DCS system by giving the command. If valve does not move, then check the supply voltage to the SOV. If voltage is not present, then check the fuse in the marshalling cabinet. If fuse is found ok, then check all the intermediate cable connections. If all connections are ok, then check the cable healthiness.
• If voltage is coming but valve does not move, then check whether there is any handle for latching the SOV or not. Because in many valves which are used in ESD system, a separate handle is present to latch the SOV for operation. If found unlatched, then latch the handle. If SOV is not getting latched, then check the interlock.

• If the On-Off valve’s SOV is still not getting any voltage from system, then check for Interlocks and Permissive from the system.
• If voltage is present but the SOV does not operate, then check the coil’s healthiness. Refer to the Solenoid Valve Problems & Solutions to learn how to troubleshoot the SOV.
• If On-Off valve is operating properly, but there is problem in the feedback, then set the feedback from the feedback box. Feedback loop has fuse and barrier/isolator also. If setting feedback does not works, then check the fuse as well as barrier/isolator also.
• Check the actuator for air passing issue. Before removing the tubing, take approval for valve operation. If found passing, then overhauling of the actuator is needed.
• If the On-Off valve is used in non-critical service then operate the valve few times with direct air. This will rouse the body of the valve.
• Check the fail action of the valve. If getting stuck in between, then valve might be actually stuck or spring of the actuator might be damaged.
• Check all the control valve accessories like quick exhaust valve, air volume booster, trip valve and vent port. There should be no issue of blockage in them. Also replace them if in doubt. 
• If there remains issue in which the vale does not opens fully or does not closes fully, then check the lock-nut given on the actuators. Adjust them if required.