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6S
CROS!:! COMPOUND AIR COMPRESSOHS
To determine the lift of the lower air valve, the gage
is first applied to the bottom flange of the air cylinder,
as illustrated in Fig. 25, and the sliding arm adjusted
until its end rests against the stop in the cylinder, in
position it is locked by means of the thumb nut.
the arm thus locked, the gage is applied to the air
valve cage and air valve, as illustrated in Fig. 27, and
if the valve has proper lift, the shoulder on the sliding
arm will just rest upon the upper side of the collal"'fff the
air valve cage, as illustrated. If the gage arm fails to
touch the stop on the valve when the shoulder on
bar rests on the collar face on
has a lift greater than standard by an amount
the distance between the stop and the gage arm.
In case the cylinders have been counterbored at the
entrance for the valve cage and valve and valve chamber
cap in such a way as to interfere with the application of
the gage, as above described, it will be found necessary,
in order to use the gage properly, to file away the small
portion of the ridge so that the cross-bar of the gage will
rest on the refaced surface of the valve chamber. In
doing this, care should be taken to avoid injury to the
refaced surface.
Never remove or replace the upper steam
with the reversing valve rod in place, as to do so
will almost invariably result in bending the rod. A bent
rod is very liable to cause a "pump failure."
When installing the reversing valve assembly in the
new type top head, it is recommended that the upper
piston first be entered in the cap nut. Then pick up the
cap nut and reversing valve assembly and insert
CROSS COMPOUND A1H COMP[U<:SSORS
69
assembly in the reversing valve bush, observing that
each piston with its rings properly enters the bush.
If
the reversing valve assembly is inserted before applying
the cap nut, the reversing valve assembly should be lifted
sufficiently to observe that the upper piston rings are
properly entered before the cap nut is screwed into place.
When assembling the sections of the piston
care should be taken to insure proper alignment
and thereby avoid possible trouble from binding of the
piston in the bushing.
It is evident that a compressor cannot compress more
air than it draws in and not that much if there is any
leakage to the atmosphere about the air cylinder. Bear
ing this in mind, practice frequently lifening at the "Air
Inlet" when the compressor is working slowly while be
ing controlled by the governor, and whenever a poor suc
tion is noted on either or both strokes, locate and report
the fault.
Any unusual click or pound should be reported as it
may indicate either a loose piston or a reversing valve
cap screw or other serious fault.
Any steam leakage that can reaeh the Air Inlet of
the compressor should be promptly repaired as such in
creases the danger of water entering the brake pipe.
Keeping the suction strainer clean is of the utmost
importanee, as even a slightly clogged strainer will great
ly reduce the capacity where the speed is at all fast. A
seriously or completely obstructed strainer, as by ac
cumulated frost, aggravated by rising steam, will in
erease the compressor speed and will also be indicated
by inability to raise or maintain the desired pressure.
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