Bulletin 22-00 A / Page 3
A4W Principle of Operation
Th
e inlet pressure enters the valve
fi lling the areas inside the piston
and inlet. Th
e pressure above the
piston prevents the piston from
moving upward. Inlet pressure travels
through passage (N), shown in the
A4W principle of operation cross-
section diagram, fi lling the chamber
underneath the diaphragm. When the
force created by this pressure acting
on the underside of the diaphragm
exceeds the force of the range spring
acting on top of the diaphragm, the
diaphragm moves upward. Th
is also
results in an upward movement of
the spring loaded pilot plug installed
directly underneath the diaphragm.
Note:
Upstream pressure,
communicated through passage (N),
is “sealed” under the diaphragm.
Th
e tight seal of the pilot plug and
pilot plug piston o-ring maintains
the inlet pressure as an independent
pressure source. Th
e upstream
pressure is not used as a pilot force
to move the piston. It simply works
against the force exerted by the range
spring which ultimately moves the
diaphragm. Th
is greatly enhances
the ability of these regulators to
operate despite the presence of system
impurities.
Th
e upward movement of the pilot
plug piston causes the pilot plug
piston seat to unseat, allowing the
pressure on top of the piston to vent
through the pilot plug, passage (P),
to the downstream side of the valve,
passage (T). Th
e lowering of the
pressure above the piston combined
with a higher inlet pressure causes it
to move upward, and the valve begins
to regulate upstream pressure at its
set point. As the valve regulates, a
bleed hole in the piston allows for
the continuous equalization of inlet
pressure to the top of the piston. A
piston seal ring ensures that this bleed
hole is the sole source of equalization.
Th
e pressure on top of the piston
varies with the position of the pilot
plug piston and the pressure drop
across the valve. As the pilot plug
A4W Principle of Operation Cross Section
A4WB Principle of Operation Cross Section (‘B’ Coil De-Energized)
system. (See Bulletin 00-20 for more
information)
Passage
Description
N
Inlet Pressure
P
Piston Pressure, Top
T
Outlet Pressure
B
Electric Wide Open Bypass
S
Electric Shut-Off
M
Manual Opening Stem
A4W Port Plate Passage Table
N
T
P
Pilot Plug
Piston
Seat
Pilot Plug
Piston Seal
O-Ring
Diaphragm
Pilot
Spring
Manual
Bypass
Stem
Pilot Plug
Piston
H
N
P
T
B
M
N
Electric
Wide
Open
Manual
Bypass
Stem
T
P
Seal Cap
