Fisher 657 - Manual (Page 6)

Instruction Manual
D100307X012
657 Size 80 and 100 Actuators
December 2010
6
Figure 3. Dimension B for Spring Adjustment
LOWER DIAPHRAGM CASING
SPRING SEAT
JAM NUT
ADJUSTING NUT
A0950‐1
B
For small spring forces, adjustments can be made by rotating the adjusting nut (key 114, figure 5). Clockwise rotation
(when viewed from diaphragm casings) of the adjusting nut will increase the loading pressure required to start
actuator stem travel, and counterclockwise rotation will decrease the pressure required to start travel. Tighten the jam
nut when adjustment is complete.
For high spring forces, it is necessary to use spacers between the lower diaphragm casing and the spring seat to isolate
spring force from the adjusting nut.
WARNING
To avoid personal injury from the compressed actuator spring snapping back to its original length, make and use the
spacers by following the instructions in the steps below.
To avoid personal injury, keep hands and tools away from the spring and spring seat as instructed in the following
procedure.
1. It is recommended that three spacers be made of 3‐inch schedule 80 pipe cut to the appropriate length specified in
step 2. If other than the recommended material is to be used, be certain that the spacers are capable of
withstanding the spring force involved. The spacers must be of equal length with ends cut squarely.
2. Measure dimension B as shown in figure 3. Cut length of spacers as follows:
a. If it is desired to decrease spring compression, make the spacers approximately 4.8 mm (3/16‐inch) longer than
dimension B.
b. If it is desired to increase spring compression, make the spacers approximately 4.8 mm (3/16‐inch) shorter than
either dimension B plus the amount of adjustment required or dimension B plus valve travel, whichever is less.
3. Whenever the total amount of adjustment required is greater than valve travel, the adjustment must be made in
two or more steps, and the amount of adjustment taken in each step must be less than valve travel.
4. Pressure the actuator to attain full travel. Cautiously insert the spacers at equal intervals around the spring seat (key
11, figure 5). The spacers must be seated squarely when in use or they may slip out of position. Keeping hands and