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).
1
THERMOSTAT
POSITIONER
Mius
Fig. 1. Typical Direct-Acting
MP953
Operation.
MAINTENANCE
EQUIPMENT NEEDED
-
Commercial cleaning solvent or degreaser
-
Pressure Gage 14003519 (0 to 30 psi [0 to 207
kPa])
-
Wrench 301572A for
MP953A
and B
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
A
Careless handling of solvents can cause permanent
respiratory or skin damage. Avoid prolonged exposure to
solvents.
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
air
pressure
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
pressure and note
the
pressure at
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.
75-5500