COPES-VULCAN INSTRUCTION MANUAL
MODEL 700 DIRECT-ACTING ACTUATOR
Rev.5 (08/10) Page 10 of
20 Form 01:P224:37
2.4 SPRING ADJUSTMENT
The spring was properly adjusted at the factory and, unless the actuator has been disassembled,
only minor adjustments should be necessary.
The initial spring preload (or bench-set) pressure is defined as the pressure at which stem motion
is initiated and is set by rotating the spring adjuster (Item 21). Rotate the spring adjuster upward in
the actuator yoke to increase the initial spring compression. Spring preload should be set to the
value given in the valve specification sheet.
The preload should be set with the stem packing loose or not installed since the value given in the
valve specification sheet is based on the assumption that there is no friction. If friction or valve
pressure is present, the following procedure should be applied:
A. Install an accurate pressure gage on the actuator air line.
B. Slowly pressurize the actuator and record the gage pressure at a point near mid-travel.
Continue to increase pressure so that the valve travels past mid-travel.
C. Slowly decrease air pressure and read the gage pressure when the valve reaches the open
position at which the previous pressure reading was made.
D. The friction force in terms of actuator pressure is equal to one-half the difference in the two
pressure readings.
E. Add this pressure to the value given in the valve specification sheet to obtain the new
precompression pressure. For example, if the opening and closing pressure readings were
36 and 30 psig (2.5 and 2.1 bar) respectively and the value in the valve specification sheet
was 6 psig (0.4 bar), then the target precompression pressure would be 9 psig (0.6 bar).
2.5 AIR CONNECTION
Accessories such as a positioner, air regulator, etc. will normally be assembled at the factory, and
the only air connection required at installation will be the supply line to the air regulator.
The size 100, 160, and 160-5 actuators will normally have 3/8" x 1/4" and 1/2" x 1/4" bushings
installed in the diaphragm cover. To increase stroking speed, such as when a volume booster is
employed, these bushings may be removed and a larger tubing line installed.
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