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.)