DeVilbiss DeVO/MC44-90 - Pilot Pressure System

SECTION 7
SERVICE INSTRUCTIONS
10. Secure compressor heads with the screws.
To replace compressor:
1. Remove the intake baffle ( 8 Fig. 14) from
the compressor intake fitting (8 Fig. 25)
and attach it to the intake fitting on the
new compressor.
2. Inspect rubber motor mounts. Replace if
damaged.
3. Install motor mounts on bottom of
compressor. Tighten them only “hand
tight”.
4. Place compressor on base assembly with
threaded rods at bottom of motor
mounts extending through holes in base.
5. Reconnect black rubber hose to com-
pressor fitting (2 Fig. 25) and secure with
hose
clamp.
6. Reconnect the compressor quick-connect
terminal (9 Fig. 25).
7. Turn unit face down with compressor
directed upward and install washers and
nuts on motor mounts.
NOTE: When tightening nuts, hold motor
mount with one hand to avoid twisting
rubber mount. A twisted motor mount may
cause excess vibration or noise.
8. Reconnect compressor intake hose (11
Fig. 14) to intake baffle (8 Fig. 14).
9. Replace cabinet covers. Ensure that all
quick-connect terminals are properly
connected before securing covers with
cabinet fasteners.
Pilot Pressure System
The compressed air in the pilot pressure
system is used to activate the four-way and
purge valves. This compressed air (approxi-
mately 22-28 PS! (152-193 KPa)) is stored in
the pilot accumulator cavity within the
manifold (1 Fig. 20). An internal check valve
allows compressed air to enter and prevents it
from escaping. The inlet side of the pilot
accumulator is connected internally within
the manifold. The outlet of the pilot
accumulator cavity is connected to the pilot
valves on the purge and 4-way by an
externally mounted “T” fitting and 1/16” (1.6
mm) tubing.
A defective check valve in the pilot
accumulator or leak in the pilot pressure
21
tubing would result in lower pilot pressure.
This, in turn, could cause a malfunction of the
four-way and/or purge valve.
To test pilot pressure:
1. Refer to Service Instruction B to open
cabinet covers.
2. Remove the pilot pressure tubing from
the pilot valve on the four-way (4 Fig. 23).
3. Attach the pilot pressure tubing to the
barbed fitting on one end of the pressure
test assembly (3 Fig. 23) that is included in
the DeVO Service Kit.
4. Attach the 1/16” (1.6 mm) hose on the
other end of the test assembly to the
fitting on the pilot valve (Point D, Fig. 23).
5. Install a pressure gauge on the test
assembly.
6. With the unit operating, pilot pressure
readings should be alternating between
22 to 28 PSI (152-193 KPa). This pressure
range may vary slightly from one unit to
another. This is essentially the same
pressure as that being exhausted by the
compressor. Therefore, it can also be used
to help determine if the compressor is
working properly.
7. If pilot pressure is low, check sieve bed
pressure.
8. If sieve bed pressures are normal, check
for leaks in the pilot pressure system. If no
leaks are found, then the check valve in
the pilot accumulator may be leaking
internally. If confirmed, the manifold
base must be replaced.
9. If sieve bed pressures are also low or rising
slowly, then:
(A) Compressor reed valves, teflon ring,
or the compressor itself may be
defective.
(B) There is a severe leak in system.
(C) One or more of unit filters may be
occluded.
. Manifold Assembly
The manifold assembly is located on the front
of the vertica! divider and has two externally
mounted valves, the four-way and purge (see
Fig. 16). These valves can be removed
separately for cleaning or replacement when
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