The Control Valves consist of the single-seated Angle Valve and Pneumatic Actuator.The process medium flows through the valve in the direction indicated by the arrow. The position of the plug (3) is changed by the signal pressure acting on the diaphragm in the actuator (8).The plug stem (6) and plug are connected to the actuator stem (8.1) by the stem connector (7). The plug stem is sealed by spring-loaded PTFE V-ring packing (4.2) or by an adjustable high-temperature packing.The control valve can be equipped with an extension bonnet with metal bellows which functions as an additional seal to comply with stringent regulations.we are gonna discuss about the procedure to assemble a diaphragm actuator to the control valve below
Depending on the arrangement of the compression springs (8.3) in the actuator, the control valve provides two different types of fail-safe action:
Actuator stem extends:
When the signal pressure is reduced or the air supply fails, the springs force the actuator stem to move downward and close the valve. When the signal pressure rises, the valve opens while acting against the force of the springs.
Actuator stem retracts:
When the signal pressure is reduced or the air supply fails, the springs force the actuator stem to move upward and open the valve. When the signal pressure rises, the valve closes while acting against the force of the springs
Procedure to assemble a diaphragm actuator
If the valve and the actuator were not assembled by the manufacturer or if the original actuator attached to the valve is to be ex-changed for an actuator of another type or size, proceed as follows:
1.Loosen the lock nut (6.2) and the stem connector nut (6.1) on the valve.Press the plug and plug stem firmly into the seat ring, then thread the stem connector nut and the lock nut down
2.Unscrew the connector stem parts (7)and the ring nut (8.2) from the actuator.Slide the ring nut over the plug stem of the valve.
3.Place the actuator on the yoke (5.3)and secure with the ring nut (8.2).Read the bench range and fail-safe action of the actuator stated on the name-plate.
4.For actuators with actuator stem ex-tends, apply a signal pressure that corresponds to the lower bench range value (e.g. 0.8 when the range is be-tween 0.8 to 2.4 bar) to the lower diaphragm chamber connection.For actuators with
actuator stem re-tracts, apply a signal pressure that corresponds to the upper bench range value (e.g. 2 bar when the range is between 0.4 to 2 bar) to the upper diaphragm chamber connection.
5.Turn the stem connector nut (6.1) by hand until it contacts the actuator stem(8.1). Turn it another 1/4 turn and secure this position with the lock nut (6.2).
6.Attach the stem connector parts (7) and screw tight. Align the travel indicator scale (5.5) with the tip of the stem connector