STEAM LOCOMOTIVE ENGINEMAN’S. Manual - part 26

Chapter 12: - Westinghouse Brake 

 

 

  

At the same time the air underneath the piston is 
compressed, the bottom receiving valve closed, 
and the air forced through the bottom discharge 
valve into the main reservoir. 

 
 

The action is continuous whilst the pump is 
working. 

 
Refer to FIGURE 14 in Annex A. 
 

12.4 

BULB TRIPLE VALVE 

 

12.4.1 

DESCRIPTION 

 
 

In the top of the valve body are situated the triple 
piston and ring, slide valve and spring, and the 
graduating valve and pin – all working on the one 
stem. 

 
 

The slide valve and bushing have the necessary 
ports and passages to control the flow of air from 
the train pipe to the auxiliary reservoir, from the 
auxiliary reservoir to the brake cylinder, from the 
train pipe to the bulb, from the brake cylinder to 
the exhaust and from the bulb to the exhaust.   

 
 

There are feed grooves in the triple piston 
bushing and in the valve face of the triple piston, 
through which flows when the triple is in the 
release position.  All are enclosed in a casing.   

 
 

Attached to the lower part of the body is the bulb, 
in the bottom of which is a drain plug.  Inside the 
bulb is screwed the siphon tube, through which 
the air passes to the bulb when the application of 
the brake is made, and through which the air 
drains when a release is made. 

 
 

A regulating plug, in which is seated the 
regulating valve and spring is fitted to the body, 
inside the bulb.  The plug has three ports  – 
namely, the valve port, the equalising port and 
the controlling port  – through which the air 
passes to the brake cylinder. 

 
Refer to FIGURE 15 in Annex A. 
 

Chapter 12: - Westinghouse Brake 

 

 

12.4.2 

CHARGING OF THE AUXILIARY RESERVOIR 

 

 

Air from the main reservoir flows to the chamber 
at the top of the rotary of the Driver’s brake valve 
and, with the brake valve handle in the full 
release or running position, flows to the train 
pipe. 

 
 

It then passes along the branch pipe to a 
passage in the cover  of the triple valve body 
leading to the train pipe side of the triple piston, 
which is moved to the full release and charging 
position.  The air flows through the feed groove 
in the triple piston bushing, past the piston ring, 
to the auxiliary side of the triple piston. 

 
 

It then flows through the feed groove on the face 
of the piston, past the slide valve, to the auxiliary 
reservoir, and continues to flow until the 
pressure in the train pipe and auxiliary reservoir 
equalise. 

 
 

12.4.3 

 APPLICATION OF THE BRAKES 

 

 

Assuming that, by way of the Driver’s brake 
valve, a reduction of pressure, say 7 lb, has 
been made in the train pipe and the brake valve 
handle has been placed in the lap position. 

 
 

The auxiliary pressure now being greater than 
that in the train pipe, the triple piston first closes 
the feed groove in the bushing and, carrying the 
graduating valve with it, opens the graduating 
port, allowing air from the auxiliary reservoir to fill 
the graduating passage in the slide valve. 

 
 

By its further movement, the triple piston moves 
the slide valve with it, towards the application 
position.  The slide valve closes the exhaust port 
from the brake cylinder and the exhaust port 
from the blub, and opens communication 
between the train line and the bulb. 

 
 

The air flows  from the train pipe to a port 
connected by the narrow cavity in the slide valve 
to a port leading to the siphon pipe, through 
which the air flows to the bulb. 

Chapter 12: - Westinghouse Brake 

 

 

  

The charging of the bulb causes a local 
reduction of train pipe pressure and influences 
the movement of succeeding triples along the 
train.  It thus tends to bring about a more 
simultaneous application of the brakes 
throughout the train. 

 
 

The charging of the bulb speeds up the 
movement of the triple to the application position.  
Air from the auxiliary reservoir then flows through 
the service port on the top of regulating plug and 
compresses the regulating valve spring, thus 
unseating the regulating valve and opening the 
valve port through which the air flows into the 
plug. 

 
 

The air then flows through the controlling port to 
the brake cylinder, where it exerts its force on 
the brake piston.  The brake piston moves 
outward, compressing the release spring, and 
causes the brake blocks to contact the wheels.   

 
 

As the pressure in the brake cylinder increases 
and acts in conjunction with the regulating valve 
spring, which has a tension of 40 lb, per square 
inch, the auxiliary pressure on top of the 
regulating valve is overcome and the valve is re-
seated. 

 
 

Air from the auxiliary continues to flow to the 
brake cylinder through the equalising and 
controlling ports in the plug, until its pressure is 
slightly less than the pressure in the train pipe.   

 
 

The triple piston will then be moved towards the 
auxiliary carrying with it the graduating valve 
only, which closes the graduating port.  The 
valve is now on lap and will remain so until a 
further reduction or release has been made. 

 
 

Assume that a further reduction of 3 lb, per 
square inch is made in the train pipe pressure.  
The auxiliary pressure again becomes greater 
than that in the train pipe and, acting on the triple 
piston, causes the latter to move towards the 
train pipe. 

 
 

 

Chapter 12: - Westinghouse Brake 

 

 

  

The triple piston carries with it the graduating 
valve, which opens the graduating port and 
allows air from the auxiliary reservoir to pass to 
the brake cylinder by way of the equalising and 
controlling ports in the plug, thus applying the 
brakes a little harder. 

 
 

The flow of air to the brake cylinder continues 
until the auxiliary pressure again becomes less 
than that in the train pipe, when the triple piston 
and graduating valve will again be moved to the 
lap position. 

 
 

Successive reduction of the train pipe pressure 
can be made, and the brake cylinder pressure 
consequently increased, until the train line, 
auxiliary reservoir and brake cylinder pressures 
are equalised.  The brake will then have been 
applied with its maximum force. 

 

12.4.4 

 RELEASE OF BRAKES 

 
 

By means of the Driver’s brake valve, the excess 
pressure from the main reservoir is allowed to 
pass to the train pipe, thus raising the pressure 
in the train pipe above that in the auxiliary 
reservoir. 

 
 

The triple piston and slide valve are then moved 
to the full release and charging position, and the 
auxiliary is charged as previously explained.  In 
the full release position, the triple valve closes 
communication between the auxiliary reservoir 
and the brake cylinder, and also between the 
train pipe and the bulb; it opens communication 
between the bulb and the atmosphere, and 
between the brake flows up the siphon pipe and 
through a port, which is connected to the bulb 
exhaust by means of the narrow cavity in the 
slide valve. 

 
 

The air from the brake cylinder flows along a 
passage in the triple body to a port in the seat, 
which is connected to the main or nipple exhaust 
by means of the broad cavity in the slide valve.  
The brake is then being released, the bulb 
emptied and the auxiliary reservoir recharged.