ain valve to the left.

[Illustration: Diagrammatic View, Up Stroke Fig. 2.]

When the main valve moves to the left, steam is admitted through port
"c" to the upper end of the cylinder on top of the piston 65, forcing it
downward. At the same time the lower end of the cylinder is connected
through exhaust cavity "b" of the main valve to the exhaust port "d",
allowing the steam below the piston to escape to the atmosphere.

44. Q. When the piston has about completed its downward stroke, what
takes place?

A. The reversing plate 69 engages the button "k" on the end of the
reversing rod 71 pulling the rod and the reversing valve down. This
movement of the reversing valve closes port "g" and the cavity in the
face of the valve connects ports "f" and "h", which allows the steam in
chamber "D" at the right of the large differential piston to escape to
the exhaust, thus allowing the main valve to move to the right,
exhausting the steam from the top end of the cylinder, and at the same
time admitting steam to the lower end, causing an upward stroke of the
piston.

45. Q. Explain the operation of the air end of the compressor.

A. The movement of the steam piston 65 is imparted to the air piston 66
by means of the piston rod. When the air piston moves up, a partial
vacuum is formed below it, and air from the atmosphere will enter
through passage "F" thence through passage "n" to the under side of
receiving valve 86b (see Fig. 2), lifting this valve from its seat, and
will fill the cylinder with air at about atmosphere pressure.

[Illustration: Diagrammatic View, Down Stroke Fig. 3.]

In the meantime the air above the piston, being compressed, will hold
the upper receiving valve 86a to its seat, and when the pressure is
slightly greater than that in the main reservoir, this pressure acting
under the upper discharge valve 86c, will lift this valve from its seat
and now the air will be free to flow through passage "G" to the main
reservoir connection. On the down stroke the action is similar, air is
taken in through the upper receiving valve 86a, while the air below the
piston is being compressed and forced past the lower discharge valve
86d, to the main reservoir. (See Fig. 3.)

46. Q. What lift should the air valves have?

A. All valves should have a lift of three thirty-second of an inch.

47. Q. At what speed should the compressor be run to obtain the best
results?

A. At 100 to 120 single strokes per minute.

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