Emerson Process Management FISHER 657 - Manual (Page 6)

Instruction Manual
D100306X012
657 Actuator (30-70 and 87)
December 2010
6
1. Provide a vise or some other method of supporting the valve and the weight of the actuator during assembly. For
direct or reverse acting valves, push the valve stem down away from the actuator while mounting the actuator.
2. Screw the stem locknuts all the way onto the valve stem. With the concave side of the travel indicator disk (key 14)
facing the valve, install the travel indicator disk on the valve stem. (Note: The travel indicator disk is not used with
size 87 actuators.)
3. Lift or hoist the actuator onto the valve bonnet:
a. For size 87 actuators, insert the cap screws and tighten the hex nuts, securing the actuator to the bonnet.
b. For all other size actuators, screw the yoke locknut onto the valve bonnet and tighten the locknut. (Note: On
small size actuators, it may be necessary to remove the indicator disk and re‐install it while lowering the actuator
on to the valve because the disk will not go through the actuator yoke opening.)
4. Do not connect the actuator stem to the valve stem at this time. Whenever the actuator is installed on the valve, it
is recommended to perform the Bench Set Spring Adjustment procedure to verify that the actuator is still adjusted
correctly.
Discussion of Bench Set
The bench set pressure range is used to adjust the initial compression of the actuator spring with the valve‐actuator
assembly “on the bench.” The correct initial compression is important for the proper functioning of the valve‐actuator
assembly when it is put into service and the proper actuator diaphragm operating pressure is applied.
The bench set range is established with the assumption that there is no packing friction. When attempting to adjust
the spring in the field, it is very difficult to ensure that there is no friction being applied by “loose” packing.
Accurate adjustment to the bench set range can be made during the actuator mounting process by making the
adjustment before the actuator is connected to the valve (see the Spring Verification Procedure).
If you are attempting to adjust the bench set range after the actuator is connected to the valve and the packing
tightened, you must take friction into account. Make the spring adjustment such that full actuator travel occurs at the
bench set range (a) plus the friction force divided by the effective diaphragm area with increasing diaphragm pressure
or (b) minus the friction force divided by the effective diaphragm area with decreasing diaphragm pressure.
For an assembled valve‐actuator assembly, the valve friction may be determined by following the procedure described
below:
1. Install a pressure gauge in the actuator loading pressure line that connects to the actuator diaphragm casing.
Note
Steps 2 and 4 require that you read and record the pressure shown on the pressure gauge.
2. Increase the actuator diaphragm pressure and read the diaphragm pressure as the actuator reaches its mid‐travel
position.
3. Increase the actuator diaphragm pressure until the actuator is at a travel position greater than its mid‐travel
position.
4. Decrease the actuator diaphragm pressure and read the diaphragm pressure as the actuator reaches its mid‐travel
position.
The difference between the two diaphragm pressure readings is the change in the diaphragm pressure required to
overcome the friction forces in the two directions of travel.