Type 667 Size 30-76 & 87
6
3. Increase the actuator diaphragm pressure until the
actuator is at a travel position greater than its mid-trav-
el 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 re-
quired to overcome the friction forces in the two direc-
tions of travel.
5. Calculate the actual friction force:
Friction
Force, = 1/2
pounds
Difference
in pressure
readings, psig
Effective
diaphragm area,
inches
2
ǒǓ
ǒ
Ǔ
Refer to table 1 for the effective diaphragm area.
When determining valve friction, you can make dia-
phragm pressure readings at a travel position other
than mid-travel if you desire. If you take readings at
zero or at the full travel position, take extra care to en-
sure that the readings are taken when the travel just
begins or just stops at the position selected.
It is difficult to rotate the spring adjustor (key 74, figure
6, 7, and 8) when the full actuator loading pressure is
applied to the actuator. Release the actuator loading
pressure before adjusting. Then re-apply loading pres-
sure to check the adjustment.
Bench Set Spring Adjustment
The term “bench set” means that the actuator is not
connected to the valve, or any other loads. Ensure that
the actuator diaphragm is at the bottom of its travel as
shown in figure 4. (Note: Some spring compression is
required to move the diaphragm to the bottom of its
travel.)
Also, provide a certified pressure gauge that will accu-
rately read the diaphragm pressure from 0 through the
upper bench set pressure marked on the nameplate.
Apply loading pressure to the diaphragm.
Stroke the actuator a few times to ensure that the
pressure gauge is working correctly, and that the ac-
tuator is functioning properly. It is important to be sure
that the actuator assembly is not binding or producing
any friction on the actuator stem movement.
Key numbers are shown in figures 6, 7, and 8.
For Direct-Acting Valves (PDTC)
1. If not already accomplished, push the valve stem
down away from the actuator to the closed position.
2. Set the diaphragm loading pressure to 0.3 bar (5
psig) over the upper bench set pressure. The upper
travel stop should be contacting the diaphragm casing.
3. Slowly decrease the pressure towards the upper
bench set pressure while checking for the first move-
ment of the actuator stem.
4. If movement occurs before or after the upper pres-
sure is reached, adjust the spring adjuster (see figure
4). Thread the adjuster up or down on the actuator
stem until the actuator stem movement is first de-
tected at the upper bench set pressure. (Note: You
may need to lower the loading pressure to reduce
spring compression, allowing the spring adjuster to
turn.)
5. Be sure the spring adjuster is adjusted to meet the
requirements of step 4 above.
6. Apply the lower bench set loading pressure to the
diaphragm. This will extend the actuator stem toward
the valve. Mark the end of the actuator stem on a
nearby surface using tape or some other method.
7. Slowly increase the diaphragm pressure until the
upper bench set loading pressure is applied. Again,
the travel stop should be against the diaphragm cas-
ing.
8. Measure the distance between the mark or tape to
the end of the actuator stem. This distance should
match the travel span shown on the travel indicator
scale (key 32).
9. If the span of travel is correct, bench set is com-
plete. Proceed to the Installing the Stem Connector
Assembly subsection.
10. If the travel span is not exact, remember the free-
length and load rate tolerances for the spring may pro-
duce a slightly different span than specified. Contact
your Fisher Controls sales office or sales representa-
tive for assistance.
For Reverse-Acting Valves (PDTO)
1. If not already accomplished, push the valve stem
down away from the actuator to the open position. Lat-
er, when installing the connector, pull up the valve
stem to the closed position.
2. Set the diaphragm loading pressure to a value less
than the lower bench set pressure (near zero). The
down travel stop should be contacting the yoke.
3. Slowly increase the pressure towards the lower
bench set pressure while checking for the first move-
ment of the actuator stem.
4. If movement occurs before or after the lower
pressure is reached, adjust the spring adjuster (see
figure 4). Thread the adjuster up or down on the actua-
tor stem until the actuator stem movement is first de-
tected at the lower bench set pressure.
5. Apply the upper bench set loading pressure to the
diaphragm. This will retract the actuator stem away
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