TM 55-203
combined dirt collector and cutout cock (fig 8-13) is
connected in the brake pipe leading to the pipe bracket.
It prevents pipe scale, sand, cinder, and other foreign
matter from entering the AB valve. The umbrella-
shaped check valve retains in the dirt chamber the
collected dirt accumulated during airbrake operation. To
remove the dirt chamber for cleaning, remove the two
nuts securing the chamber to the collector body.
connects the branch pipe to the brake pipe. It prevents
excessive moisture that may be deposited in brake pipe
from passing into the branch pipe and thence to the AB
valve.
i.
Retaining Valve.
(1) The retaining valve is a three-position,
manually operated, pressure-retaining exhaust valve
car near the brake staff The handle positions are plainly
identified as follows:
Figure 8-10. Exterior view of A-2-A quick-service
value.
(a) EX (Direct Exhaust) handle pointing
emergency air pressure. Letters cast on a lug projecting
downward.
from the separation plate identify the reservoirs. The
(b) HP (High Pressure Retain) handle 45to
letters AUX on one side of the lug indicate the auxiliary
60clockwise from EX position.
reservoir and the letters EMERG on the other side of the
lug indicate the emergency reservoir.
(c) SD (Slow Direct Exhaust) handle 135
to 1500 clockwise from EX position.
f. Automatic Air-Operated Slack Adjuster (when
equipped)
(2) The retaining valve is calibrated to regulate
the air pressure as follows:
(1) The automatic slack adjuster (fig 8-3) is a
device for maintaining a uniform running standard piston
(a) With the handle in direct exhaust the
travel.
brake cylinder pressure exhausts freely to the
atmosphere.
(2) The piston travel, when over that for which
the adjuster is set, is automatically shortened by a small
(b) With the handle in high pressure retain
cylinder having a piston with a pawl which engages with
it retards the exhaust of air from the brake cylinder down
and turns the ratchet nut The adjuster cylinder takes air
to a predetermined pressure and then retains that
from the brake cylinder through a small pipe which is
amount (approximately 16 to 22 psi).
tapped into the brake cylinder at a distance from the
pressure head approximately equal to the desired piston
the brake cylinder pressure exhausts slowly to the
travel.
atmosphere.
(3) When piston travel allows the piston
packing cup to pass the port where the adjuster pipe is
(3) The calibration of the retaining valve is such
connected to the cylinder, brake cylinder pressure is
as to permit the blowdown of a 435-cubic-inch reservoir
admitted to the adjuster cylinder which moves the piston
volume from an initial charge 80 psi pressure for each of
the full stroke of the cylinder, compresses a spring and
its three positions in the time specified below:
moves the pawl over two teeth of the ratchet nut.
Position
Pressure blowdown
Time (in seconds)
(4) When the airbrake is released and the brake
cylinder piston moves back past the port, the air in the
Direct Exhaust
70 to 10 psi
Less
than
3
adjuster cylinder exhausts into the nonpressure end of
seconds
the brake cylinder. This permits the piston spring in the
High Pressure
adjuster cylinder to force back the adjuster piston, and
Retain
60 to 40 psi
33 to 43 seconds
by means of the pawl makes 1/8 of a turn of the ratchet
Slow Direct
nut.
Exhaust
60 to 40 psi
17 to 22 seconds
g. Combined Dirt Collector and Cutout Cock.
A
8-14
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