Bench Set - Emerson Fisher 667NS2 Instruction Manual

667NS2 Actuator
March 2022
2. Tighten the locknuts together, use a wrench on these locknuts, and screw the valve stem either into the stem
connector to lengthen travel or out of the stem connector to shorten travel.
3. Cycle the actuator to check travel. If travel is not equal to the specified travel, adjust and check travel until correct.
Tighten the stem connector cap screws when correct travel is obtained.
4. Thread the stem locknuts against the stem connector.

Bench Set

Discussion of Bench Set
The bench set pressure range is used to adjust the initial compression of the actuator spring with the actuator
assembly "on the bench." The correct initial compression ensures that the valve‐actuator assembly will function
properly when it is put in 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 (see the Mounting
the Actuator on the Valve Procedure) by making the adjustment before the actuator is connected to the valve.
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, determine valve friction as 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.
5. Calculate the actual friction force:
(
Difference
Friction
Force, in pressure
=1/2
readings, psig
pounds
Refer to table 1 for the effective diaphragm area.
8
) ( )
Effective
diaphragm area,
X
2
inches
Instruction Manual
D103472X012