Actuators come in many design types. But the most commonly used in my experience in relation to mechanical valves are either pneumatic or electric actuators. They share the same understanding of how their torque operates a valve. When sizing an actuator for valves, accuracy is very important. If an actuator is sized by an inexperienced person, and he/she doesn`t size it correctly, this could be very dangerous. At the worst a major incident in a plant or refinery resulting in millions lost and/or damage to persons and the environment.
When considering the torque values to operate the valve, one must consider: How much torque is required to fully open and fully close the valve. If the valve gets stuck in mid function of opening or closing the valve a safety factor must also be considered sizing the actuator.
Valve torque requirements
Below are the valve torque requirements needed for correctly sizing the right actuator for the right valve.
This is the amount of torque required to start the movement of a valve from the closed position.
This is the amount of torque required to maintain movement of the valve between open and closed positions.
This is the amount of torque required to seat a valve into its closed position.
Maximum shaft torque
The torque required to permanently deform or break the valve stem.
The recommended safety factor is 25% for valves that requires 100 in-lb torque to open, the actuator’s break torque at 125 in-lbs.
true Double Block & Bleed Valves
When sizing an actuator for true double block and bleed valves like our AS-Schneider Twin Ball Design (Taurus Series). Two actuators are needed to properly actuator the valves if actuators are required by the user. Since the Taurus Series DBB Valves are designed for maximum safety with 2 balls inside the valve body, the customer would need to mount one actuator per ball & stem. Pneumatic and electric actuators can be mounted directly onto the valve stem with a mounting plate.
(Image source: © AS-Schneider)