[Figs. 3342], [3343] and [3344] represent the Westinghouse automatic air brake applied to an engine and tender, and in the following figures details of the construction of various parts are shown.

VOL. II.LOCOMOTIVE AIR BRAKES.PLATE XXXIII.
[Large
image
(88 kB).]
Fig. 3342.
[Large
image
(Fig. 3343;
60 kB).]
Fig. 3343.Fig. 3344.

The pump governor, which is shown at g in [Fig. 3326], of a modern freight locomotive, is shown in section in [Fig. 3345].

[Large
image
(117 kB).]

Fig. 3345.

The pump governor is employed for the purpose of cutting off the supply of steam to the pump when the air pressure in the train pipe exceeds a certain limit, say 70 lbs. per square inch.

Its operation is as follows:

When valve 10 is (by means of hand wheel 8) screwed home to its seat the steam is entirely shut off from the steam cylinder, but by operating wheel 8 to unscrew spindle 9, valve 10 is permitted to open and let the steam pass through a and b to the steam cylinder which operates, forcing air into the reservoir and thence into the train pipe. A pipe from the train pipe connects to the upper end of the pump governor, hence air from the train pipe passes around the stem 14 to the upper side of the thin diaphragm 18, which is held in its position by the spring 12 with a force sufficient to enable it to resist, without moving, a pressure of 70 lbs. per square inch. But when the pressure exceeds 70 lbs. per square inch it forces the diaphragm down, pushing down valve 13 and allowing the steam in a to pass up through valve 13 and out of the exhaust pipe 6. The steam pressure in a being thus reduced, that in b acts on the under side of the valve, causing it to rise and seat itself and thus cut off the supply of steam to the pump.