to the atmosphere. A
reducing-valve is attached to the driver's valve, and in the normal or
running position of the latter reduces the pressure of the air flowing
from the main reservoir to the train-pipe by 10 or 15 lb. per sq. in.
From the engine a train-pipe runs the whole length of the train, being
rendered continuous between each vehicle and between the engine and
the rest of the train by flexible hose couplings. Each vehicle is
provided with a brake-cylinder H (fig. 1), containing a piston, the
movement of which applies the brake blocks to the wheels, an
"auxiliary air-reservoir" G, and an automatic "triple-valve" F. The
auxiliary reservoir receives compressed air from the train-pipe and
stores it for use in the brake-cylinder of its own vehicle, and both
the auxiliary reservoir and the triple-valve are connected directly or
indirectly with the train-pipe through the pipe E. The automatic
action of the brake is due to the construction of the triple-valve,
the principal parts of which are a piston and slide-valve, so arranged
that the air in the auxiliary reservoir acts at all times on the side
of the piston to which the slide-valve is attached, while the air in
the train-pipe exerts its pressure on the opposite side. So long as
the brakes are not in operation, the pressures in the train-pipe,
triple-valve and auxiliary reservoir are all equal, and there is no
compressed air in the brake-cylinder. But when, in order to apply the
brake, the driver discharges air from the train-pipe, this
equilibrium is destroyed, and the greater pressure in the auxiliary
reservoir forces the triple-valve to a position which allows air from
the auxiliary reservoir to pass directly into the brake-cylinder. This
air forces out the piston of the brake-cylinder and applies the
brakes, connexion being made with the brake-rigging at R. The purpose
of the small groove n which establishes communication between the two
sides of the piston when the brakes are off, is to prevent their
unintended application through slight leakage from the train-pipe. To
release the brakes, the driver, by moving the handle of his valve to
the release position, admits air from the main reservoir to the
train-pipe, the pressure in which thus becomes greater than that in
the auxiliary reservoir; the piston and slide-valve of the
triple-valve are thereby forced back to their normal position, the