3
Refrigerating Specialties Division
Adjustment
With the solenoid pilot electrically energized, proceed as described
above for Inlet Pressure Regulators.
Type A4WB (See Fig. 4)
Description
The Type A4WB is an Inlet Pressure Regulator with a Pilot Electric
Wide-opening, or Bypass, variation. When the integrally mounted solenoid
is energized the main valve is wide open thereby bypassing the regulator
function, that is, not regulating. However, in the wide open mode the
regulator will still require the 0.14 bar (2 psi) minimum pressure difference
to be fully open. When the solenoid is de-energized the valve functions as
an inlet pressure regulator.
Purpose
The Type A4WB frequently is used in the wide-open mode when maximum
refrigeration capacity from an evaporator is required. During the defrost of
the evaporator, the regulator pilot solenoid is de-energized, thus functioning
as a defrost relief regulator or for high pressure limit protection. Also, this
regulator can be used in the wide open mode for evaporator pump out
prior to defrost.
When used in a discharge pressure line, it can, when de-energized,
hold back enough pressure for some heat reclaim or defrosting function
and then, when energized, allow the discharge pressure to decrease to
a lower level.
Principles of Operation
The operation of the A4WB is the same as that described for the A4W on
page 2, when operating as a regulator (Pilot Solenoid De-energized). When
the solenoid is energized the upstream pressure from passage N bypasses
the underside of the diaphragm and is fed directly to the top of the
piston, whereby, provided a 0.14 bar (2 psi) pressure difference exists
across the main valve, the Modulating Plug will be held wide open.
Adjustment
With the solenoid pilot electrically de-energized, proceed as described
above for Inlet Pressure Regulators.
Type A4WD (See Fig. 5)
Description
The Type A4WD is a Dual Inlet Pressure Regulator capable of regulating
two different pressure set-points. When the integrally mounted S6A
Pilot Solenoid is energized, the regulator is controlling the lower of the
two set-points, which must be adjusted on the pressure pilot over the
center of the main valve. When the solenoid is de-energized, the regulator
is controlling the higher of the two set-points, which must be adjusted on
the bolt-on (outboard) pressure pilot.
Purpose
The Type A4WD uses are similar to those for the A4WB except that,
instead of operating in a wide-open position when the pilot solenoid is
energized, the regulator is controlling at some pre-set level.
Typical uses include capacity control of an evaporator at two different
pressure levels to regulate temperature, or evaporator pressure control
combined with defrost or washdown pressure relief.
Principles of Operation
The operation of the A4WD is similar to that described for the A4W on
page 2. When the Pilot Solenoid is energized, upstream pressure from
passage N is made available to both diaphragms. Since the path of
least resistance will be through the pilot having the lower set-point
(lower range spring force), that pilot will control.
When the Pilot Solenoid is de-energized, the upstream pressure from
passage N can flow only to the high pressure pilot, which will then
control the regulator.
Adjustment
Electrically de-energize the solenoid pilot and adjust the modular (bolt-
on) pressure pilot for the desired high pressure setting following the
adjusting procedure as described above. 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 A 4 W P
Description
The Type A4WP is an Inlet Pressure Regulator whose set-point 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 specifically 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 var y 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
Fig. 3 – A4WS
Fig. 4 – A4WB
Fig. 5 – A4WD
