l2.1.4.3 If the brake pipe pressure is reduced at an emergency
rate in the Control Valve, quick action chamber pressure
will position the diaphragm assembly and spool in the
extreme upward position. In this position, the quick action
chamber is now only connected to exhaust Choke M, which
provides a blowdown of the quick action chamber air. With
the spool valve in the upper position, the stem unseats the
vent valve pilot valve and exhausts the air pressure on the
top of the vent valve check valve carrier. Brake pipe pressure
below the vent valve check valve and carrier forces
that valve open, creating a large opening for rapid brake
pipe air exhaust. The choke in the top cover controls the
volume of air that must be exhausted at the pilot valve, thereby
permitting fast opening of the large vent valve. The diaphragm
assembly and spool valve will remain in the upper
position until brake pipe and quick action chamber have
been nearly exhausted, at which time the force of the air
spring above the check valve and carrier will move the assembly
downward, positioning the valve in its normal position.
2.1.5 RELEASE
2.1.5.1 In Release Position, an increase in the brake pipe
pressure is called for. When this higher pressure is admitted
into the brake pipe chamber above the large diaphragm
in the service valve all of the combined downward forces
position the diaphragm assembly and stem to permit the air
in Passage 16, that leads to the brake cylinder application
pipe, or brake cylinder relay valve control pipe, to vent to
atmosphere through the service application valve stem and
Passage 10 in the pipe bracket. The continued drop of air
pressure in the limiting valves permits the spring within the
service limiting valve to move the spool downward and, with
the build-up of brake pipe pressure, the emergency limiting
valve piston is held down. Both valves, upon resetting, provides
a means for a rapid exhaust of all air. The air on the
face of the charging valve diaphragm is also vented to atmosphere,
which permits the spring to move the charging
valve to its normal position when brake cylinder application
pipe pressure reduces to a value below 31/2 to 41/2 psi.
3.0 MAINTENANCE SCHEDULE
3.1 SIX MONTHS
At least once every six months, or more frequently if service
conditions so indicate, the disposable air strainer of the
1" Combined Cut-Out Cock and Strainer MUST BE replaced
and the dirt chamber removed and completely cleaned and
then replaced.
IMPORTANT: All operating property safety procedures and