de
valve seat and allow air from the auxiliary reservoir to flow to the top
of the emergency piston 8, forcing the latter downward and opening
emergency valve 10. The unseating of the emergency valve allows the air
in chamber "Y" to escape to the brake cylinder, thus permitting brake
pipe pressure in chamber "a" to lift the check valve 15 and flow to the
brake cylinder through chambers "Y" and "X", until brake cylinder and
brake pipe pressure nearly equalize, when the check valve is forced to
its seat by the check valve spring 12, preventing the air in the
cylinder from escaping back into the brake pipe again. The emergency
valve and piston will now return to their normal position. At the same
time port "s" in the slide valve registers with port "r" in the slide
valve seat, and allows air from the auxiliary reservoir to flow to the
brake cylinder. This sudden discharge of brake pipe air into the brake
cylinder has the effect on the next triple valve, which in turn vents
brake pipe air that affects the following triple valve and so on
throughout the train.

NEW YORK AIR BRAKE

AIR COMPRESSOR

161. Q. What do Figures 19 and 20 represent?

A. These are cross-sectional views of the New York compressor.

162. Q. Of what does the valve gear of this compressor consist?

A. Of two main valves, actuated by tappet rods which enter into the
hollow piston rods, and are moved by tappet plates, which are fastened
to the steam piston heads.

163. Q. How is the admission and exhaust of steam controlled?

A. The valve under the cylinder at the right controls the flow of steam
to and from the cylinder at the left; while the valve under the cylinder
at the left controls the flow of steam to and from the cylinder at the
right.

164. Q. Explain the operation of the steam end of the compressor.

[Illustration: Low Pressure Piston Moving Upward. High
Pressure Piston at Rest. Fig. 19.]

A. Assuming both pistons are at the bottom of their cylinders, when the
compressor throttle is opened, live steam will flow to both steam chests
"B" (see Fig. 19), and through port "o" to the under side of the piston
"T" and through port "g" to the upper side of piston "H". The steam
under piston "T" will force it upward, and when it very nearly completes
its stroke, the tappet plate "Q" will engage the button on the end of
the tappet rod "P", moving the main valve "C" to its upper position. In
this position the exhaust cavity "r" in the m