Refrigerating Specialties Division
4
Energize the solenoid pilot and adjust the integral pressure pilot
for the desired low pressure setting following the same procedure.
The modular (bolt-on) pilot MUST be adjusted for a set-point
HIGHER than the integral pilot or the regulator will always be
controlling at the lower set-point whether the pilot solenoid is
energized or de-energized.
Type A4WP
Description
The Type A4WP is an Inlet Pressure Regulator whose setpoint
can be compensated by a remote pressure. Typically the remote
pressure would be a pneumatic signal from a thermostat or
controller, but it can also be a refrigerant pressure. The remote
pressure is fed into the bonnet of the regulator where it is capable
of changing the set-point on a 1:1 basis. That is, a 0.07 bar (1.0
psi) change in the remote pressure will create a 0.07 bar (1.0 psi)
change in the set-point of the regulator.
Although not specifi cally described in this bulletin, the A4WP
is also available with any of the “S”, “B”, “D” and “OE” features
mentioned elsewhere
.
Purpose
The Type A4WP can be used to vary an evaporator or condenser
pressure to match a changing load condition. A pneumatic
thermostat-controller modulates the air pressure applied to
the top of the diaphragm as the temperature at the thermostat
changes. Whether used as part of a cooling system to control
evaporator pressure, or as part of a Heat Reclaim system to control
condensing pressure, a rise in temperature at the thermostat
must cause a decrease in controlled air pressure. (Normally
this is known as a “Reverse Acting” thermostat-controller.) The
decrease in air pressure will lower the regulator set-point and
produce a lower inlet pressure and lower evaporator or condenser
temperature. Conversely, a drop in temperature at the thermostat
must cause an increase in air pressure, with a resultant increase
in evaporator or condenser temperature. Usually, the controller
modulates the air pressure from 0.21 to 1.0 bar (3 to 15 psig)
throughout its control range.
The A4WP can be used as a Differential Pressure Regulator if the
regulator outlet pressure is connected to the bonnet.
Principles of Operation
The Type A4WP operation is the same as the A4W described above
except that the set-point is changed (compensated) on a 1:1 basis
by the pressure that is fed into the bonnet.
If the A4WP is part of a pneumatically operated control system,
the air must be clean, dry and oil free. To avoid the possibility of
moisture from compressed air freezing in the bonnet or in other
parts of the control system, a dehydrated air system must be used
whenever it may come in contact with sub-freezing temperatures.
This is particularly true if the regulator is controlling suction gas
fl ow at temperatures below freezing.
Adjustment
If the A4WP is part of a pneumatically operated control system.
the controller must be adjusted according to the manufacturers
instructions to obtain the optimum system performance. To
adjust the pressure regulator. disconnect the air line and follow
the instructions, above listed for the Type A4W. This setting
represents the lowest inlet pressure the regulator will allow,
thus providing a low limit feature to the regulator. Next, connect
the air line. From this point the regulator’s set-point will be
increased on a 1:1 ratio with the air pressure increase.
If the A4WP is compensated by a remote refrigerant pressure, the
setpoint of the regulator (the inlet pressure it will be controlling)
will be equal to the sum of the remote pressure and the pressure
equivalent to that made by the range spring adjustment. If the
remote pressure is the regulator outlet pressure, then the valve
will control an inlet pressure equal to the outlet pressure plus the
Range Spring setting. Or, said another way, the Regulator will be
a Differential Pressure Regulator because the set-point will be
the difference in pressure across the regulator.
Type A4WOE (See Fig. 2-2,2A)
Description
The Type A4WOE is an Outlet Pressure Regulator with an external,
fi eld installed connection to the downstream (outlet) pipe of the
regulator. This connection is not furnished with the regulator. The
regulator will tend to open on a drop in outlet pressure below
set-point and will tend to close on a rise in outlet pressure above
set-point.
Although not described in this bulletin, the A4WOE is also available
in combination with the “S”, “B”, “D” and “P” features described
elsewhere.
Purpose
The Type A4WOE will modulate fl ow of refrigerant fl uid to
maintain a constant downstream pressure as set-for, despite
fl uctuations in load. However, once closed, the regulator can do
nothing further to reduce downstream pressure. This reduction
must come from system capacity. The regulator cannot maintain
set-for pressure if uncontrolled blanch lines feed into the main
pipeline downstream of the A4WOE Regulator.
Typical applications are as a hold back or crankcase pressure
regulator to prevent pressure rise in a suction main, or to prevent
too low a plant suction pressure by putting an artifi cial load on the
main from a higher pressure source.
Principles of Operation
The outlet pressure is sensed under the Diaphragm through the
external tube which has been installed in the fi eld to the outlet
pipe downstream of the main valve. When the force created by the
outlet pressure acting under the Diaphragm is less than the force
of the Range Spring, the pilot is open, allowing upstream pressure
from passage N to fl ow to the top of the Piston. This causes the
Piston to force the Modulating Plug to open to maintain a constant
outlet pressure. A decrease in the outlet pressure allows the
Range Spring to open the pilot further, allowing more pressure
on top of the piston and opening the Modulating Plug further.
An increase in outlet pressure will lift the Diaphragm against
the force of the Range Spring, allowing the Pilot Plug to start
to close. The pressure on top of the Piston is decreased
and the Closing Spring acts to reduce the opening of the
Modulating Plug and the fl ow of fl uid through the regulator.
Fig. 5 - A4WD
Fig. 2-2 - A4WOE
