DeVilbiss DeVO/MC44-90 - Page 20

SECTION 7
SERVICE INSTRUCTIONS
The opening and closing of the purge valve
can be observed by attaching pressure gauges
to the test points (1, Fig. 22) on the manifold.
When the purge is activated there will be a
sudden increase in pressure in one bed and a
sudden decrease in the other as the cycle
changes. When the purge is deactivated the
pressures in the sieve beds will continue to
increase and decrease respectively. You will
hear the oxygen being transferred when the
purge is activated and the exhaust will also be
heard when the valve is deactivated.
A purge valve stuck in the activated position
will cause both sieve beds to pressurize simu!-
taneously and activate the alarm system. The
red long cycle and high pressure lights will be
illuminated. See Section 5, Alarm System. If
the purge valve remains in a deactivated
position, the alarm system will not be
activated but the following symptoms may be
noticed:
(1) No sudden increase and decrease of sieve
bed pressures when cycle changes. They
will go up and down gradually.
(2) Only the exhaust can be heard when unit
cycles.
(3) Possible drop in oxygen concentration,
especially at the higher liter flows.
There are several reasons for the purge valve
to malfunction. The cause of failure must be
determined before the proper corrective
action can be taken. Some reasons for purge
failure are:
(1) Continuous or no voltage to pilot valve on
purge.
(2) Little or no pilot pressure.
(3) Foreign matter inside valve preventing
spool from shifting.
(4) Defective or damaged purge.
(5) O-rings on sleeve may be worn pre-
venting the valve from shifting properly.
To test purge valve:
1. Connect pressure gauges furnished in the
DeVO Service Kit to the test points (Fig.
22) located on the manifold.
2. Turn unit on and observe the green
indicator light (8 Fig. 12) labeled purge on
the MC board. When this light is
illuminated (approximately 1.0 seconds)
the purge should be activated and there
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should be a sudden increase and decrease
of pressure in the respective sieve beds.
The absence of this purging action indi-
cates that the purge was not properly
activated. Refer to the normal cycling
sequence on page 24.
3. Place the test leads of a volt meter across
the terminals (See test position B, Fig. 16)
located on top of the pilot valve.
Approximately 12-15 VDC should be
measured while the green purge indica-
tor light is illuminated (voltage will be
supplied for approximately 1.0 seconds).
İf this reading is not obtained, check for
loose or broken wires from the purge
valve to the MC board. If no loose or
broken wires are found, replace the MC
board.
4. Test for pilot pressure. See Service
Instruction "J", Pilot Pressure System.
5. If 12-15 VDC is medsured at connecting
leads to purge and pilot pressure is
normal then the purge valve is either
defective or foreign matter has gotten
inside valve causing it to malfunction. In
either case the purge valve must be
removed to clean or replace it.
To remove purge valve:
1. Unplug unit from wall outlet.
2. Refer to Service Instruction B to open
cabinet covers.
3. Disconnect the two wires from terminals
on pilot valve (4 Fig. 16).
4. Remove the pilot pressure tubing from
pilot valve (5 Fig. 16).
5. Remove the two allen head cap screws
from top of purge using an allen wrench.
The top or valve body and gasket can now
be removed.
NOTE: Do not remove the valve manifold.
The valve manifold will remain on the unit
whether you are cleaning or replacing the
valve.
To clean purge valve:
1. Remove the two allen head screws from
the top of purge valve. The top of the
valve or valve body can now be removed
along with the pilot valve. The valve
manifold will remain on the unit. A
rubber gasket located between valve