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685 Piston Actuator
May 2013
Actuator Mounting
The following procedure describes how to mount a 685 actuator on a pushdowntoclose 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 2 and 3.
If you purchase a 685 actuator for field installation on a control valve, mount the actuator on the valve and secure it to
the bonnet with the eight 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.
CAUTION
To avoid damaging the 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. With the valve assembled and actuator mounted, make sure the valve plug is in the closed position. Then turn the
two stem locknuts (if present) all the way onto the stem thread.
2. Starting with the cylinder fully retracted, manually, or with air pressure, extend the piston rod extension to the
specified valve travel.
3. Attach the stem connector (key 18), clamping the piston rod (key 17) extension to the valve stem. Be sure you also
attach the feedback arm and travel indicator.
4. Cycle the actuator to check availability of desired total travel and that the valve plug seats before the cylinder
reaches the end of its stroke. You can make minor travel adjustments, if necessary, by loosening the stem
connector slightly, tightening the locknuts together, and (with the valve plug off the seat) screwing the stem either
into or out of the stem connector by means of a wrench on the locknuts.
5. If the total travel is adequate, tighten the stem connector (key 18) securely, lock the stem locknuts (if present)
against the connector, and adjust the indicator scale (key 22) on the yoke (key 21) to show valve plug position.
6. Provide a gauge, if necessary, to measure the pressure to the actuator. Make a final adjustment on the positioner to
set the starting point of valve travel and to obtain full travel for the given instrument range.
Handwheel Operation
If manual operation is required, the actuator should be equipped with a manual handwheel.
CAUTION
To avoid damage to actuator parts and difficult operation of actuator handwheels, open the bypass valve (key 66) before
using a handwheel.
The bypass assembly is furnished only when a handwheel actuator is specified. The bypass allows the pressure to
equalize on either side of the piston, so that the manual actuator can be used to position the control valve. Flow
through the bypass tubing is controlled by an angle needle valve, which is operated manually. This valve should be
closed when air pressure is being used to operate the actuator.
Key numbers referenced in the following steps are shown in figure 3. Refer to table 6 for turns-per-inch of travel
specifications.
6
Instruction Manual
D103626X012
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