In a one-way-acting actuator, the air chamber on one side of the diaphragm is opposed to the other side of the diaphragm using an internal spring. The internal spring, called the range spring, moves the actuator in the opposite direction when the air pressure in the air chamber is reduced. The range spring also acts like a fail-safe mechanism, allowing the actuator to rotate to either an open or closed position when the air supply to the actuator is interrupted. Depending on the external shape, the spring is mounted adjacent to the diaphragm or adjacent to the diaphragm plate.
The actuator stem is connected to the diaphragm plate and is supported by guides through the top of the yoke. When the air pressure increases and the diaphragm moves, the plate moves in a corresponding form. Linear motion is transmitted directly to the actuator stem, which pushes the closing element within the valve. The actuator is mounted on the valve body with a yoke to indicate the position of the actuator or industrial valve, and to support the actuator rod, so that the actuator rod and the valve stem are connected. It also makes attachment easy to install. For diaphragm actuators, the most common connection method between the valve body and the actuator is a threaded yoke nut. Use a clamp to prevent accidental rotation of the actuator stem and valve stem, and the clamp should be equipped with an indicator to indicate the actuator or valve position.
For the convenient one-way acting diaphragm mechanism, the air signal from the controller to the actuator has a double function. It first provides the positioning signal, and secondly, it provides the power to generate the required thrust, which should be able to overcome the process force and friction. , Gravity, Closing Element Weight, and the counterforce created by the Range Shot. Diaphragm actuators have two structures of forward action and reverse action. For the positive acting configuration (Figure 5.9), compressed air is fed to the actuator, which extends the actuator stem and closes the valve.
This also means that, in the event of air loss, the actuator will retract the actuator stem and keep the valve open, keeping it open. For the reverse acting configuration (Figure 5.10), when air pressure is delivered to the actuator, the stem contracts and the valve opens. If the air supply or air pressure is interrupted, the actuator moves to the extended position and the valve closes.