Traction Rolling Stock - Indian Railways Institute of Electrical ...

which has the requisite inter connection between valves by means of cored passages in the
casting itself, the only external pipe connections being from the main reservoir and brake pipes
and atmosphere.
7.3.5 Brake Controller
The brake controller handle has five positions as under ;-
(a) I ...... Release and Running
(b) II ...... Full service EP
(c) III ...... Lap (for auto application)
(d) IV ...... Service automatic
(e) V ...... Emergency
The positions of brake controller is shown in fig. 7.3.5.
Lower brake cylinder pressures with self-lapping feature as explained later are
obtainable for intermediate positions of the handle between positions I and II, the actual brake
cylinder pressure being dependent upon the degree of handle movement away from position I.
7.3.6 E.P. brake system
Fig 7.3.6 is a block diagram explaining the functioning of the EP brakes. When an EP
application is to be made, the controller handle is moved from position I towards position II. (Fig
7.3.5). First the holding train wire is energized which energizes the holding magnet valves
throughout the train, thus closing the exhaust from the brake cylinders. The application valves are
then energized via the application train wire. This causes compressed air to flow the brake
cylinders from the main reservoir pipe, the rate of flow being controlled by a choke (not shown in
the figure). If the application valve remains energized, the pressure in the brake cylinder builds up
to 3.5 kg/cm², any rise of pressure beyond this value being prevented by the 'limiting valve'.
Between positions I and II the self-lapping mechanism controls the brake cylinder
pressure. Fig.7.3.5 shows the self-lapping mechanism schematically. Movement of the controller
handle towards II compresses a spring in a small control cylinder, the amount of compression
depending upon the degree of handle movement. This spring acts on piston at the back of which
air pressure from the brake cylinders of the leading bogie is applied. When the brake cylinder
pressure exceeds the value corresponding to the controller handle position, the mechanism deenergises
the application train wire, thus limiting the brake cylinder pressure to value
corresponding to the handle position. If the brake cylinder pressure drops on account of leakage
etc. The application wire is re-energized. If the handle is moved backwards, the holding wire is deenergized
till the brake cylinder pressure drops to the required value. The self-lapping mechanism
thus automatically controls the brake cylinder pressure at definite value corresponding to the
handle position and enables graduated application and release. In position II & V the application
and holding circuits are energized by 'positive acting' contacts bypassing the self-lapping
mechanism, the pressure then being limited by the limiting valve as explained earlier.
Two indication lamps are provided on the Driver's desk a green lamp to indicate that EP
brake control supply is available and an orange lamp which lights up when brake application is
made if pressure has built up in all the bogies, which is detected by a pressure switch, the
pressure switches in all the coaches being connected in series. The extinguishing of the green
lamp indicates total failures of EP brakes necessitating use of the automatic brakes to control the