Refrigerating Specialties Division
2
regulator will vary its pressure set point as load
demand varies as sensed by the thermal bulb.
A4AT DIRECT ACTING
TEMPERATURE REGULATOR
The A4AT Regulator modulates flow in response to
the temperature variation sensed by its thermal bulb.
A special temperature pilot replaces the standard
A4A pressure pilot. A rise in temperature will cause
the valve to open; a drop will cause it to close. This
valve responds only to temperature changes and is
not a pressure regulator.
Operation
Temperature changes of the cooled medium are
sensed by the thermal bulb of the pilot. As the bulb
is warmed the charge in the thermal element ex-
pands, creating an increase in pressure on the
element diaphragm. The resulting force pushes a
push pin against the pilot diaphragm, lifting it off the
seat, allowing inlet pressure to reach the top of the
piston of the main regulator, causing the main valve
to open. A drop in the temperature at the thermal
bulb causes the opposite to happen, closing the
main valve.
Adjustment
In addition to the pressure gauge at the inlet, a
thermometer is needed in the cooled medium. Set
the regulator pilot to the desired temperature by
turning the adjusting stem. The temperature scale is
only approximate and minor adjustments will be
necessary after the system has been in operation
for a while to obtain the desired temperature setting.
A4AOT REVERSE ACTING
TEMPERATURE REGULATOR
The A4AOT Regulator modulates flow in response
to the temperature variations sensed by its thermal
bulb. A special temperature pilot replaces the
standard A4AO pilot. A drop in temperature will
cause the valve to open; a rise will cause it to close.
This valve responds only to temperature changes
and is not a pressure regulator.
Operation
Temperature change of the controlled medium is
sensed by the thermal bulb of the pilot. As the bulb
is warmed, the charge in the thermal element ex-
pands. The resulting force is transmitted to the pilot
plug by a push rod, causing the pilot to close. This
in turn causes the main valve to close. A drop in the
temperature at the thermal bulb causes the opposite
to happen, thus allowing the main valve to open.
Standard range is -20
o
F to 80
o
F (-30
o
C to +30
o
C).
Also available 60
o
F to 140
o
F (20
o
C to 60
o
C). Maxi-
mum temperature to which thermal bulb can be
exposed is 150
o
F (65
o
C).
The A4AOTS Regulator combines the Reverse
Acting Temperature Regulator with Electric Shut-
Off. It operates the same as the A4AOT when the
solenoid pilot is energized and closes when the
solenoid pilot is de-energized regardless of the
temperature setting or pressure in the regulator.
Manual Opening Stem
All Type A4 Regulators are provided with a manual
opening stem. To open the regulator manually, back
the stem out (turn counter-clockwise) until it stops.
To put the regulator into automatic operation, turn
the stem in (clockwise) until only the flats on the
stem protrude from the packing nut.
Fig. 2
