STEAM LOCOMOTIVE ENGINEMAN’S. Manual - part 25

Chapter 12: - Westinghouse Brake 

 

 

  

POSITION NO 2: -   Lap position, holding brakes applied 

after a non-automatic application 

 

§ 

In Position No. 2, all parts are blanked and 
communication between passages “F” and “E” is 
cut off. 

 

 

 

POSITION NO 3: -  Application position admitting air from 

main reservoir to straight air pipe. 

 

§ 

In Position No. 3, air from the main reservoir is 
admitted to passage “F” through port “A” in the 
rotary valve, and port “D” in the seat.  The 
exhaust passage “E” is blanked in this position. 

 
 

Refer to  SECTION 12.5 for details of the No. 4 automatic 
brake valve. 

 
12.2 

NO 7 SINGLE HEAD PUMP GOVERNOR 

 

12.2.1 

PURPOSE 

 
 

The pump governor is an appliance for 
automatically controlling the pressure in the main 
reservoir.  It is fixed on the steam pipe leading 
from the boiler to the pump and consists of three 
vertical chambers mounted above a horizontal 
steam passage. 

 
 

The upper chamber contains the diaphragm 
stem, a regulating spring, and a washer.  The 
regulating plug is screwed into the top of  the 
chamber, is locked in position, and is protected 
by a cap nut.  A small relief port in the side of the 
chamber allows the escape of any air that may 
leak past the diaphragm plates from the main 
reservoir.  

 
 

Attached to the middle chamber is the main 
reservoir connection with an air strainer in the 
passage.  In this chamber are the diaphragm 
plates and their supportive ring, the pin valve, 
the pin valve spring and guide, and the pin valve 
port, which leads through a passage to the vent 
port and to the top of the governing piston. 

 
 

 

Chapter 12: - Westinghouse Brake 

 

 

  

The lower chamber contains the governor piston 
and its spring.  The steam valve piston passes 
through the bottom of the lower chamber and 
works in a guide provided in the chamber.  It is 
secured to the governor piston by two nuts.   

 
 

There is a drain port in the bottom of the lower 
chamber to allow the escape of the steam and 
air, a pipe connection being fitted to it on the 
outside.  The steam passage contains the steam 
valve and its seats. 

 
  

With the valve resting on the upper seat, steam 
is prevented from entering under the governor 
piston, and when resting on the lower seat the 
steam supply to the pump is cut off.  This valve 
is in its normal position with the lower seat open.   

 
 

Refer to FIGURE 13 in Annex A. 

 

12.2.2 

OPERATION 
 

 

When the pump is working, air is delivered into 
the main reservoir, and from there passes under 
the diaphragm plates in the middle chamber.  
When the pressure of air below the diaphragm 
plate is greater than the resistance of the 
regulator spring, which is 90 lbs, the spring is 
compressed and the diaphragm centre is forced 
up, resulting in the pin valve being lifted and the 
pin valve port being opened. 

 
 

The main reservoir air then flows to the top of the 
governor piston, and also out of the vent port, 
and the governor piston is forced down, 
compressing the piston spring under it and 
shutting down the steam valve, thus stopping the 
supply of steam to the pump.  The main reservoir 
air escapes slowly through the vent port, keeping 
the pump working slowly 

to prevent 

condensation. 

 
 

When the pressure below the diaphragm plates 
becomes less than the resistance of the 
regulating spring, the diaphragm centre is forced 
down, closing the pin valve port and cutting off 
the main reservoir air from the top of the 
governor piston.   

Chapter 12: - Westinghouse Brake 

 

 

  

The governor piston spring and the steam under 
the steam valve then lifts the valve, the air on top 
of the governor piston escapes through the vent 
port to the atmosphere, and steam is again 
supplied to the pump. 

 
12.3 

OPERATION OF THE SINGLE STAGE WESTINGHOUSE 
PUMP 

 

12.3.1 

ACTION OF THE STEAM END THROUGH ONE 
DOUBLE STROKE 

 
 

On opening the starting valve, steam passes 
through the pump governor and then through a 
passage in the cylinder wall into the main valve 
chamber between the differential piston heads of 
the main valve. 

 
 

It then passes through a passage into the 
reversing valve chamber, giving equal pressure 
in both chambers.  In the main valve chamber, 
the steam acting on the inside of the large head 
of the main valve overcomes the steam acting on 
the inside of the small head and moves the main 
valve in the direction of the large head. 

 
 

The main valve carries the slide valve with it, and 
steam is admitted through a port to the bottom of 
the cylinder thus forcing the piston up.  When the 
piston  nears the end of the up stroke, the 
reversing plate attached to the top of the piston 
strikes the shoulder of the reversing rod and lifts 
the rod.  As the rod is lifted the reversing valve is 
carried up with it. 

 
 

As the end of the stroke is reached, the 
reversing valve closes the exhaust port and 
opens the admission port to the outside of the 
large head of the main valve. 

 
 

The steam on the outside of the large head of 
the main valve, assisted by the steam acting on 
the inside of the small head, then overcomes the 
steam acting on the inside of the large head and 
consequently moved the main valve in the 
direction of the small head, carrying the slide 
valve with it. 

 
 

 

Chapter 12: - Westinghouse Brake 

 

 

  

The exhaust cavity in the slide valve connects 
the steam port to the bottom of the cylinder and 
the main exhaust passage, and allows the steam 
in the bottom of the cylinder to escape to the 
atmosphere. 

 
 

At the same time, steam is flowing from the main 
valve chamber through a port to the top of the 
cylinder, forcing the piston down.  When nearing 
the end of the down stroke, the reversing plate 
strikes the button on the end of the reversing rod 
and carries the rod and reversing valve down. 

 
 

At the end of the stroke, the reversing valve 
closes the admission port and opens the exhaust 
port from  the outside of the large head of the 
main valve, and steam on the outside of the 
large head escapes to the atmosphere. 

 
 

The steam on the inside of the large head again 
overcomes the steam on the inside of the small 
head, and the main valve again moves in  the 
direction of the lage head, carrying the slide 
valve with it. 

 
 

In this position the exhaust cavity of the slide 
valve connects the top of the cylinder to the 
atmosphere, and steam flows through the 
admission port to the bottom of the cylinder to 
again start the piston on its up stroke. 

 
12.3.2 

ACTION OF THE AIR END THROUGH ONE 
DOUBLE STROKE 

 
 

When the piston is on its up stroke, a vacuum is 
formed in the lower end of the air cylinder.  
Atmospheric pressure lifts the bottom receiving 
valve and air flows into the cylinder, following the 
piston until it reaches the end of its stroke. 

 
 

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

 
 

On the down stroke a vacuum is formed in the 
top of the cylinder.  Atmospheric pressure lifts 
the top receiving valve and the air flows into the 
top end of the cylinder, following the piston until 
the end of the stroke.