Instruction Manual
D104483X012
785C Actuator
May 2022
22
Actuator Mounting
The following procedure describes how to mount a 785C actuator on a push down to close valve so that the piston rod
to valve plug stem connection allows full travel and proper shutoff. Key numbers referenced in the following steps are
shown in figures 24 through 38 and 48. If you purchase a 785C actuator for field installation on a control valve, mount
the actuator on the valve and secure it to the bonnet with the bonnet-to-actuator bolts. The stem connection should
then be made up to clamp the actuator stem and valve plug stem together to provide proper valve travel.
WARNING
When moving the piston rod with loading pressure applied, exercise caution to keep hands and tools out of the piston rod
travel path. If the loading pressure is accidentally disconnected, personal injury and property damage is possible is
something is caught between the piston rod and other control valve parts.
NOTICE
The 785C spring extend actuator spring load will force the piston rod to extend out of the cylinder, and it can come into
contact with the valve stem during actuator mounting.
If the valve stem is allowed to remain in the up position (towards the actuator) during mounting, it can interfere with the
actuator mounting, possibly damage valve stem threads or bend the valve stem. Be sure the valve stem is pushed down
(into the valve body), away from the actuator while mounting.
To avoid damaging the valve plug seating surfaces, do not rotate the valve plug while it is seated. Also avoid damage to the
valve plug stem by careful use of tools during travel adjustment.
1. Using the given lifting eye bolts (key 2215), hoist the actuator vertically oriented. Slowly lower it over the valve
taking care not to contact the stem in manner that could cause damage.
2. Once the actuator is seated on the bonnet yoke, install the studs through the yoke mounting plate. Install the nuts
and tighten to the appropriate torque as specified in the applicable valve instruction manual.
CAUTION
Before pressurizing the cylinder, ensure the plastic plugs are removed from the pneumatic cylinder and replaced with
appropriate metal plugs or other pressure-retaining devices.
3. Starting with the piston (key 2206) at the top of the pneumatic cylinder, manually, or with air pressure, extend the
piston rod (key 2350 or 2402) to the specified valve travel.
4. With the valve plug on the seat, attach the valve stem connector (key 4301) by inserting the socket head cap screws
(key 4302), clamping the piston rod (key 2350) to the valve stem. Make sure to attach the travel indicator
(key 5000) and anti-rotator plate (key 4850) if supplied. Confirm proper operation and check travel, travel indicator
adjustment, etc. before placing the actuator into operation.