A. The purpose of the equalizing reservoir is to furnish a larger volume
of air above the equalizing piston than is found in chamber "D", thus to
enable the engineer to make a graduated reduction of the pressure above
the equalizing piston.
97. Q. What defect will cause the brake pipe and main reservoir pressure
to equalize when the handle is in running position?
A. This may be caused by leakage past the rotary valve, defective body
gasket, or leakage by the feed valve or its case gasket. To determine
which part is at fault, close the cut-out cock under the brake valve
and move the handle to service position, exhausting all air from chamber
"D" and the brake pipe; return the handle to lap position. Leakage of
air past the rotary valve is generally into the brake pipe port which
allows the air to come in under the equalizing piston, thus forcing it
upward, unseating the brake pipe exhaust valve, allowing this air to
escape to the atmosphere at the brake pipe exhaust port. Leakage past
the body gasket allows air to enter chamber "D", above the equalizing
piston, holding it in its lower position, keeping the brake pipe exhaust
port closed, thereby preventing the escape of this air to the
atmosphere. Since the capacity of the equalizing reservoir and chamber
"D" is small, such a leak will cause the black hand to quickly move up
to the position of the red hand. To determine if the leakage be in the
feed valve or its gasket, recharge the brake pipe to some pressure below
the adjustment of the feed valve, then place the handle in lap position.
If the black hand on the air gauge remains stationary, it is fair to
assume that the trouble is in the feed valve or its gasket, as in this
position of the brake valve the feed valve is cut out.
98. Q. With the engine alone, the brake pipe pressure will equalize with
that in the main reservoir, while when coupled to a train the pressure
will remain at that for which the feed valve is adjusted; where is the
trouble?
A. This is caused by light leakage of main reservoir air into the brake
pipe, and may come past the rotary valve, body gasket, or feed valve,
and with the lone engine is sufficient to raise the brake pipe pressure
to that in the main reservoir; while, when coupled to a train, the brake
pipe leakage of which is greater than this amount, this leakage will not
be noticed.