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CROSS COMPOUND AIR COMPRESSORS
and high pressure air pistons. The upward movement
causes the high pressure air
10 to compress the
air in the upper end of the high pressure air cylinder to
its final pressure, and to discharge it through passage v,
discharge valve 41, and through passage
tv
into the
main reservoir. Steam is exhausted from the upper end of
the low pressure steam cylinder through passage
d,
chamber D and 'passage e to the atmosphere.
After the low pressure steam piston 8 has completed
its upward stroke, as explained, the lower end of the
pressure air cylinder, is of course, filled with air
compressed from the lower end of the low pressure air
and the lower end of the low pressure steam
is filled with steam exhausted from the lower
end of the high pressure steam cylinder. However, just
as the low pressure steam piston 8 has completed its
upward stroke, steam is by-passed through three by-pass
grooves x from the lower to the upper side of this piston,
thereby preventing an accumulation of back pressure
in the lower end of the high pressure steam cylinder.
At this stage of the cycle, also, the upper end of the
low pressure air cylinder is filled with air at atmospheric
pressure and the upper end of the high pressure steam
is filled with live steam; but just before the
pressure steam piston 7 completes its downward
valve plate 18 engages the button end of the
reversing valve rod, moving it downward and carrying
the reversing valve to its extreme lower positioll, thereby
closing passage n, cutting off the supply of live steam to
chamber N, and connecting passage
tn,
cavity Band
passage b, thereby exhausting steam from chamber N
on the faee of the large main valve piston. Since the
OPEHATION
21
pressure against the inner side of the large piston
IS
now greater than the pressure exerted against the inner
side of the small piston 1, the piston valve moves to the
or in the direction of chamber N, and all parts are
in the position shown in Plate 2.
Live steam is now supplied from passage a, through
chamber A, and passage
g,
to the lower end of the high
pressure steam cylinder, forcing upward the high pres
sure steam piston 7 which, as already explained, carries
with it the low pressure air piston 9. At this time also,
steam is exhausted from the upper end of the high pres
sure steam cylinder, through passage
c,
chamber D and
passage d, into the upper end of the low pressure steam
At the same time-
the low pressure air piston 9 is compressing
the air in the upper end of the low pressure air cylin
der and forcing same past the intermediate valves
39 and through passage
u
into the upper end of the
high pressure air cylinder, and
(b)
air at atmospheric pressure is drawn into
the lower end of the low pressure air cylinder,
through the air strainer, lower inlet opening, past the
lower inlet valve 38 and through ports s
Again it will be ob:served that the steam in the low
pressure steam cylinder and air in the
air cylinder act simultaneously
pistons, steam being exhausted from the upper end of
the high pressure steam cylinder through passage c,
chamber D and passage d, to the upper end of the low
pressure steam cylinder, in which it acts expansively on
the low pressure steam piston. At the same time steam
is exhausted from the lower end of the low pressure
"
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