DeVilbiss DeVO/MC44-90 - Purge Valve

section.)
SERVICE INSTRUCTIONS
4. Test for pilot pressure. See Service
Instruction “J”, Pilot Pressure System.
5. If 12-15 VDC is measured at connecting
leads to four-way and pilot pressure is
normal then four-way valve is either
defective or foreign matter has gotten
inside valve causing it to malfunction. In
either case the four-way valve must be
removed to clean or replace it.
To remove four-way valve:
1. Unplug unit from wall outlet.
2. Refer to Service Instruction B to open
front cover.
3. Disconnect the two wires from terminals
on pilot valve (14 Fig. 16).
4. Remove the pilot pressure tubing from
pilot valve (13 Fig. 16).
5. Remove the two allen head cap screws (2
Fig. 16) from top of four-way using an
allen wrench. The top or valve body and
gasket can now be removed.
NOTE: Do not remove manifold. The
manifold will remain on the unit whether you
are cleaning or replacing the valve.
To clean the four-way valve:
1. Remove the two allen head screws from
the top of four-way valve. The top or the
valve body can now be removed along
with the pilot valve. The valve manifold
will remain on the unit. A rubber gasket
located between the valve body and valve
manifold should also be removed.
2. Remove the 4 screws from the ends of the
valve so that the end plates, plastic
spacers and spring can be removed. Note
position of these parts.
3. Carefully remove spool from valve body.
Using a non-metallic rod or dowel with a
diameter no greater than the sleeve,
slowly push the sleeve out either end of
the valve body. (Note: Pushing too fast
will cause o-rings to roll and jam).
Remove the “O” rings from the sleeve and
inspect them for signs of damage. If they
are damaged, they should be replaced
using valve rebuild Kit #MC44D-707 prior
to reinstallation of the sleeve into the
valve body.
5. Wash the spool and sleeve (less “O” rings)
in warm, soapy water until all of the
17
deposits have been removed. The plastic
spacers and spring may also be cleaned if
needed. (Important: never try to scrape
the spool or sleeve or use an abrasive
substance for cleaning. This would
adversely affect the operation of the
valve).
6. Rinse the spool and sleeve thoroughly
and dry with a soft, clean, lint-free cloth.
Reinstall or replace “0” rings on sleeve.
7. Ensure that the air passages (ports) in
both the valve body and manifold are free
of any foreign matter. A ciean lint-free
cloth or a compressed air hose can be
used to clean these.
8. Carefully push sleeve into valve body
(turning it slightly) so you do not cut or
knick the o-rings. To ensure proper
placement of spool, use white plastic
spacer and push until spool is flush with
valve body.
9. Reassemble remaining parts of valve in
reverse order.
To replace four-way valve:
1. Align valve body and gasket on manifold.
Ensure that gasket is aligned properly.
Secure with two allen head screws.
2. Attach pilot pressure tubing to pilot-
valve.
3. Reconnect the two wires on terminals of
pilot valve.
4. Replace the front cover and secure with
cabinet fasteners.
H. Purge Valve
Like the four-way, the pneumatically
operated purge valve (13 Fig. 11) uses an
external pilot valve. This pilot valve will
receive a signal (approximately 12-15 VDC)
from the MC board at the beginning of each
cycle (except the first) causing the purge to be
activated for approximately 1.0 seconds.
While the purge is activated, oxygen is
transferred from the pressurized bed to the
depressurized bed and the exhaust port is
closed. When the purge is deactivated the
exhaust port opens allowing nitrogen to be
exhausted. It is released through a muffler (6
Fig. 19) located on the vertical divider behind
the compressor.
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