Instruction Manual
D104483X012
785C Actuator
May 2022
23
Maintenance
Actuator parts are subject to normal wear and must be inspected and replaced when necessary. The frequency of
inspection and replacement depends on the severity of service conditions.
WARNING
Avoid personal injury and property damage from sudden release of process pressure or bursting of parts. Before
performing any maintenance operations:
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Do not remove the actuator from the valve while the valve is still pressurized.
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Always wear protective gloves, clothing, and eyewear when performing any maintenance operations.
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Disconnect any operating lines providing air pressure, electric power, or a control signal to the actuator. Be sure the
actuator cannot suddenly open or close the valve.
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Use bypass valves or completely shut off the process to isolate the valve from process pressure. Relieve process pressure
on both sides of the valve. Drain the process media from both sides of the valve.
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Vent the power actuator loading pressure and relieve any spring pre-compression.
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Use lock‐out procedures to be sure the above measures stay in effect while you work on the equipment.
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The valve packing box may contain process fluids that are pressurized, even when the valve has been removed from the
pipeline. Process fluids may spray out when removing the packing hardware or packing rings, or when loosening the
packing box pipe plug.
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Check with your process or safety engineer for any additional measures that must be taken to protect against process
media.
Instructions are given below for complete disassembly of the actuator, seal replacement, and O-ring replacement. When
inspection or repair is necessary, disassemble the actuator only as far as is required to accomplish the job. Key numbers
referenced in the following steps are shown in figures 18 through 53.
Actuator Removal
The following procedure is for the removal of the actuator from the valve.
WARNING
To avoid personal injury or equipment damage, use proper lifting and rigging practices while lifting the actuator assembly.
To avoid personal injury due to the sudden uncontrolled movement of parts, do not loosen the stem connector hex nuts
when the stem connector has spring force applied to it.
1. Ensure the valve and actuator are de-energized (mechanical, pneumatic, and electric) and appropriately isolated.
Disconnect the actuator tubing from the pressure connections on the pneumatic cylinder head flange and end
flange (key 2201 and 2210) and positioner. Provisions may need to be made to the actuator and spring if the design
is spring extended.
For 785C Spring Extend actuator:
It may be necessary to apply a temporary loading pressure to the bottom cylinder
pressure connection to move the piston rod away from the valve stem during removal. If it is not possible to provide
a temporary loading pressure, exercise caution when removing the actuator to prevent damage or personal injury.
2. Disconnect the stem connection by removing socket head cap screws (key 4302) from the valve stem connector
(key 4301).
