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OPERATION
In a direct-acting (n.o. valve) system, an increase in
control (branch/pilot) air pressure forces the Actuator
diaphragm and cup assembly downward, forcing the valve
stem down to proportionally close off the flow through the
valve (Fig. 1).
In a reverse-acting (nc. valve) system, an increase in
control (branch/pilot) air pressure forces the Actuator
diaphragm and cup assembly upwards, forcing the valve
stem up to proportionally increase the flow through the
valve.
In Actuators without Gradutrol Relays or positive
positioners, branchline pressure is applied to the
diaphragm. In Actuators with Gradutrol Relays or positive
positioners, up to full main air pressure is applied to the
diaphragm to ensure the valve is positioned proportionally
to the pilot pressure (the branchline pressure output from
the controlling device).
MAINTENANCE
EQUIPMENT NEEDED
Commercial cleaning solvent or degreaser
VISUAL INSPECTION
Check periodically for leaks, loose fittings, and other
visible problems.
CLEANING
Clean the Actuator with a commercial cleaning solvent or
degreaser.
A
WARNING
Careless handling of solvents can cause permanent
respiratory or skin damage. Avoid prolonged exposure to
solvents.
A
1
THERMOSTAT
Fig. 1. Typical Direct-Acting MP953 Operation.
OPERATIONAL CHECK 2
Vary the branchline (pilot) pressure through the
operational range of the Actuator in both directions. The
valve should open and close smoothly.
ADJUSTMENTS
CHECK ADJUSTMENT ON MP953A, B, E, F
Install gages in the main and pilot air lines.
Main
should be greater than or equal to the
top of the sequencing range (span): 13 psi (90 kPa) is
the minimum main pressure for the device to function.
Slowly increase
pilot
which the valve stem begins to travel. This pressure
should be within kO.75 psi (5 kPa) of the start point
setting of theMP953AandB'ForMP953EandF, the
pressure should be within +l psi (7 kPa) of the start
point.
Continue increasing the pilot pressure until the valve
stem stops traveling. This pressure should be the start
point pressure plus the range (span) setting.
POSITIONER
the
pressure and note
pressure at
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