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15
14
CROSS COMPOUND AIR CuMPRESSORS
Intermediate piston No, 4 crosses a
connecting
with passage c, controlling the flow of steam to the upper
end of the high pressure steam cylinder, and also the ex
haust into the upper end of the low pressure steam cyl
inder,
Intermediate piston No, 3 crosses a port connecting
with passage e, controlling the exhaust of steam from
either end of the low pressure steam
Intermediate piston No, 2 crosses a port connecting
with passage
g,
causing steam to be admitted to the lower
end of the high pressure steam cylinder or exhausting
steam from this cylinder into the lower end of the low
pressure steam
The recent addition of four grooves to the inner end
of the large main valve bushing 107 (Fig, 5) serves to
prevent possibility of vibration of the main valve when
the compressor is operating under a very restricted
throttle, Under this condition should the reversing valye
fail to supply and maintain steam pressure on the outer
of the large piston equal to that on the inner side,
these by-pass grooves serve to equalize the pressure on
the large piston before the by-pass grooves in the small
piston cylinder balance the pressures at that end, The
large piston is thus brought into full balance regardless
of the condition of the reversing valve and related parts,
thereby preventing rebound of the main valve and
vibration,
The piston
reversing valve is a multiple
device (similar to the main valve) consisting of four
pistons of the same size except the upper piston which
is slightly smaller (see Fig. 3). A port
z
through the
piston valve equalizes the pressures at each end and the
DESCRIPTION
difference in size of the end pistons is such as to com
pensate for the weight of the reversing valve and rod so
that these parts are always in balance,
Chamber B between the two upper pistons is
in communication with the exhaust port e, Chamber K,
between the two lower. pistons is at all times connected
to the steam inlet passage a, The reversing valve cap
serves as a bush for the upper piston and permits re
moval of the reversing valve,
Relief valves 155 (section B-B) and 156, Fig. 3,
which are constructed as shown by the small section at
the foot of Fig. 3, are for the purpose of preventing ex
cessive pressure development in the low pressure air
cylinder, due to leakage past the high pressure or inter
mediate discharge valves which might otherwise interfere
with normal operation of the compressor.
Old and New Standard Air Compressors
The preceding description applies to the two new
standard
81/2"
air compressors which are intended for
use with steam pressures up to 300 and up to 400 pounds
as already stated. The principal difference between the
present standard and the former standard compressor
steam pressures up to 275 pounds) is that the new
compressors employ materials suitable for the
steam pressures and temperatures, and new type top
heads. A piston type reversing valve performs the same
function as the slide valve type but is subject to less
friction, resulting in less strain on the reversing valve
rod and insuring better performance. The main valve
in the new top head is of one piece construction and the
small end piston is the same size as the intermediate
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