Refrigerating Specialties Division
2
Principles of Operation (See Fig. 1 & 1A)
The outlet pressure is sensed under the diaphragm through the sensing tube,
which is part of the Flange Ring-tube assembly. 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 pressure to enter on top of the piston.
This causes the power piston to force the modulating plug to open to maintain
constant outlet pressure. 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 the outlet pressure
will lift the diaphragm against the force of the range spring, allowing the pilot
plug to start closing. The pressure on top of the power piston is decreased and
the closing spring acts to reduce the opening of the modulating plug and the
flow of fluid through the regulator. The pressure on top of the power piston
is controlled by the flow through the pilot seat and the bleed through a bleed
hole in the power piston and through the clearance between the piston and
cylinder. A minimum of 0.14 bar (2 PSIG) pressure drop across the regulator
is required to open it fully.
The A4AO Outlet Pressure Regulator therefore opens on a drop in the outlet
pressure below its set point and closes on a rise in outlet pressure above
its set point. The outlet pressure set point is not appreciably affected by
variations in the inlet pressure.
Manual Opening Stem
All Type A4A Regulators are provided with a manual opening stem. To open the
regulator manually, back the stem out (turn counterclockwise) 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.
Adjustment
Install a pressure gauge at the regulator gauge port in the A4AO Adapter
next to the sensing tube. Back the adjusting stem all the way out to stop
(counterclockwise). This will reduce the set-point to its lowest level and cause
the valve to close. Operate the system until the outlet pressure is lower-than
desired. Slowly turn in the adjusting stem (clockwise) until the desired outlet
pressure is reached.
A4AO Outlet Pressure Setting Ranges
Approx. Pressure Change
Factory Set Point
Set Point Ranges
per Turn of
(unless otherwise
Adjusting Screw
specified)
V:500mm hg to 8.3 bar
1.7 bar (25 psi)
2.8 bar (40 psig)
(20in hg to 120 psig)
D:5.2 to 19.3 bar
3.7 bar (53 psi)
9.7 bar (140 psig)
(75 to 280 psig)
TYPE A4AOE (See Fig. 2)
Description
A4AOE Outlet Pressure Regulator,
Remote Sensing Connection
This regulator allows control of downstream pressure at a point remote from
the outlet of the regulator. The pressure from the desired sensing point is
connected directly to the A4AOE adapter at Fitting 7A in place of the Flange
Ring-tube Assembly 20 shown for the A4AO. Thus the regulator will control
the pressure at the sensing point. The regulator operation and adjustment
is the same as for A4AO.
Type A4AOS (See Figs. 2, 3, and 4)
Description
A4AOS Outlet Pressure Regulator
With Electric Shut-Off
The A4AOS Pressure Regulator controls outlet pressure when the mod-
ular solenoid is energized, and closes when the solenoid pilot is de-ener-
gized regardless of the pressure setting or pressure in the regulator. The
Modudapter (Fig. 2, item 28A) is used only with the A4AOS. The Pilot Solenoid
is mounted on Pad #1 of the Modudapter along with Moduplate, item #52,
mounted on Pad #2 with “S” showing to the outside of the regulator.
Adjustment: With the solenoid energized, proceed as with the A4AO.
Installation
All regulators are packed for maximum protection. Unpack carefully. Check
the carton to make sure all flanges and other items are unpacked. Save the
enclosed instructions for the installer and eventual user.
Do not remove the protective coverings from the inlet and outlet of the
regulator until the regulator is ready to be installed. Protect the inside of
the regulator from moisture, dirt and chips before and during installation.
When welded or brazed flange connections are used, all slag, scale and loose
particles should be removed from the flange interior before the regulator
is installed between the flanges. It is advisable to install a close-coupled
companion strainer (RSF) at the inlet of the regulator to help protect it from
any foreign material in the system.
The A4A series of regulators will give optimum performance if mounted
in a horizontal line in a vertical position with the manual opening stem on
bottom. Where other positions are desired, the factory should be consulted,
please give application and piping details. The regulator must be installed
with the arrow on the valve body pointing in the direction of the fluid flow
for the regulator to function properly. Backward flow through the regulator
is uncontrolled and will vary with the valve model and the reverse pressure
drop encountered. The regulator is not a check valve.
Tighten the flange bolts and nuts evenly to provide proper seating of the
flange gasket and to avoid damage to gaskets or flanges. (See Flange Bolt
Torque Table, page 12). Avoid using the regulator flange bolts to stretch or
align pipe. Even the heavy duty semi-steel body of an A4A can be distorted,
causing the precision parts to bind.
The regulator should be installed in a location where it is easily accessible
for adjustment and maintenance. The location should be such that the
regulator cannot be easily damaged by material handling equipment.
When it is necessary to insulate the regulator (and companion strainer),
the insulation should be installed to provide access to the regulator (and
companion strainer) for adjustment and maintenance. Do not insulate the
solenoid coil and coil housing. Proper indicating gauges should be installed
to be easily visible to the operating engineer for system checking and
adjusting purposes.
Disassembly and Assembly
Refer to Figs. 2, 3 and 4 in this section.
Before disassembling any A4A type regulator, read the information in this
bulletin and Bulletin RSB, Safety Procedures for Refrigerating Specialties
Division Refrigeration Control Valves.
Before a regulator is removed from the line or disassembled in the line, make
sure that all refrigerant has been removed from the regulator, including the
bonnet where applicable, and the close coupled strainer. The regulator must
be isolated from the rest of the system in a safe manner. When pumping down
to remove the refrigerant, the manual opening stem 33A must be turned
out (counterclockwise) to make sure the valve is open.
All A4A Regulators General Procedure
The construction of the regulator and the method of disassembly are
relatively simple, but some procedures must be followed to avoid damage.
The following describes the procedure for the basic A4A; special instructions
for other types are included in other appropriate sections.
