Actuator, Pneumatic (Type 755)

The Type 755 actuator is a pneumatically operated, spring opposed diaphragm actuator designed specifically to fit the Research
Control Valve body-bonnet assembly. The unit is available in two sizes: one to fit the 1/4 in. (6 mm) valve and a larger version to
fit the 1/2…1 in. (12…25 mm) valves. It provides a smooth linear extension of the valve stem upon an increasing instrument
signal. A decrease in instrument signal causes the stem to retract and open the valve. Downward closing force is generated by
instrument air on top of the diaphragm. An increasing pressure in the diaphragm cavity opposes the force of the spring and extends
the stem, closing the valve. The unit is designed to retract the stem, opening the valve, should the instrument signal fail.

FUNCTION

The 1/4 in. (6 mm) size 755 actuator normally operates in response to a 3…15 psi (0.2…1 bar) change in instrument signal, or a
12 psi (0.8 bar) range. This signal range causes the valve to stroke a distance of approximately 7/16 in. (11 mm). The standard spring
has a deflection rate of 25 pounds per 1/8 in. (3 mm) and operates against an effective diaphragm area of approximately 7 in.2
(4516 mm2 ). The 1/2 in. (12 mm) size 755 actuator also normally operates in response to a 3…15 psi change in instrument signal, or
a 12 psi (0.8 bar) range. This signal range causes the valve to stroke a distance of approximately 9/16 in. (14 mm). The standard spring in the 1/2 in. (12 mm) unit has a deflection rate of 30 pounds per 1/8 in. (3 mm) and operates against an effective diaphragm area of approximately 11 in.2 (7096 mm2).

STANDARD FEATURES

Compact lightweight design
1/4 in. (6 mm) unit = 1.81 pounds
(excluding handwheel and body-bonnet assembly)
1/2 in. (12 mm) unit = 4.01 pounds
(excluding handwheel and body-bonnet assembly)
Stainless steel external hardware
Powder coated for increased corrosion resistance
Simple design for easy maintenance

OPTIONAL FEATURES

Choice of other signal ranges: 3…27#, 6…30#
All stainless steel housing, 1/2 in. (12 mm) unit only, see
actuator Type 890
Manual handwheel for operation without air; can also be used
as an up-travel stop
Side-mounted positioner, for a top-mounted positioner, see
Type 759