Instruction Manual
D102602X012
657NS Actuator
November 2012
9
If you are adjusting to 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 supply pressure line that connects to the actuator diaphragm casing.
2. Increase the actuator diaphragm pressure. Record 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. Record 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:
Friction
Force,
pounds
=1/2
Difference
in pressure
readings, psig
(
)
X
Effective
diaphragm area,
inches
2
(
)
Refer to table 1 and 3 for the effective diaphragm area.
When determining valve friction, you can make diaphragm pressure readings at a travel position other than mid-travel
if you desire. If you take readings at the zero or at the full travel position, ensure that the readings are taken when the
travel just begins or just stops at the position selected.
The spring adjustor is difficult to rotate. Release the loading pressure before adjusting, then re-apply loading pressure
to check the adjustment.
Bench Set Adjustments
1. Monitor loading pressure carefully when making adjustments. Do not exceed the maximum pressure specifications
of either the loading regulator or the actuator casings (refer to table 1 for Maximum Diaphragm Casing Pressure).
2. Each actuator spring has a fixed pressure span. Changing the spring compression shifts the span up or down to
make valve travel coincide with the loading pressure range.
3. For sizes 40 through 70, turn the spring adjustor (key 12, figure 2 or 3) into the yoke to shift the span up or turn the
spring adjustor out of the yoke to shift the span down. For size 80, remove the spring case assembly (key 35, figure
4) by removing the cap screws (key 6, figure 4). Then rotate the spring adjustor (key 12, figure 4) to shift the span.
Replace the spring case assembly and screws.
If the actuator has a side-mounted handwheel assembly, turn the handwheel clockwise to close the valve.
For successful operation, the actuator stem and valve plug stem must move freely in response to the loading pressure
change on the diaphragm.
Operation
In a direct-acting diaphragm actuator, an increasing loading pressure causes the actuator stem to move downward,
compressing the spring. When the diaphragm pressure is decreased, the spring moves the actuator stem upward. This
