Purge Valve - Sunrise Medical DeVilbiss 505DZ Service Manual

C O M P O N E N T T E S T I N G , R E P A I R & R E P L A C E M E N T

Purge Valve

Like the four-way, the pneumatically operated purge valve uses
an external pilot valve.This pilot valve will receive a signal
(approximately 12-15 VDC) from the PC board at the beginning
of each cycle (except the first) causing the purge to be activat-
ed for approximately 1.2 seconds.While the purge is activated,
oxygen is transferred from the pressurized bed to the depres-
surized 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 an exhaust muffler located on
the back of the manifold assembly.
The opening and closing of the purge valve can be observed by
attaching pressure gauges to the test points on the manifold
assembly.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 simultaneously and activate the alarm
system.The appropriate red indicator lights will be illuminated.
If the purge valve remains in a deactivated position, the alarm system
will not be activated but the following symptoms may be noticed:
• No sudden increase and decrease of sieve bed pressures
when cycle changes.They will go up and down gradually.
• Only the exhaust can be heard when unit cycles.
• Possible drop in oxygen concentrations, 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 cor-
rective action can be taken. Some reasons for purge failure are:
• Continuous or no voltage to pilot valve on purge.
• Little or no pilot pressure.
• Foreign matter inside valve preventing spool from shifting.
• Defective or damaged purge.
• O-rings on sleeve may be worn preventing the valve
from shifting properly.
To test purge valve:
1. Remove the front cabinet.
2. Connect pressure gauges furnished in the service kit to
the test points located on the manifold assembly.
3. Turn unit on and observe the green indicator light labeled
purge on the PC board.When this light is illuminated
(approximately 1.2 seconds), the purge should be activated
and there should be a sudden increase and decrease of
pressure in the respective sieve beds.The absence of this
purging action indicates that the purge was not properly
activated. Refer to the Normal Operating Sequence.
4. Place the test leads of a volt meter across the terminals
located on the pilot valve. Approximately 12-15 VDC
should be measured while the green purge indicator light
is illuminated (voltage will be supplied for approximately
1.2 seconds). If this reading is not obtained, check for loose
or broken wires from the purge valve to the PC board. If
no loose or broken wires are found, replace the PC board.
5. Test the pilot pressure. Refer to Pilot Pressure System.
6. If 12-15 VDC is measured 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 (Figure 41):
1. Unplug the unit from the wall outlet.
2. Remove the front cabinet.
3. Disconnect the two wires from terminals on pilot valve.
4. Remove the pilot pressure hose from pilot valve.
5. Remove the two allen-head cap screws from the top of
purge using an allen wrench.The top of 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 purge valve:
1. Remove the two allen-head screws from the top of the
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
body and manifold should also be removed.
2. Remove the screws from the ends of the valve so that the
end plates, plastic spacers, and spring can be removed.
Note the position of these parts.
3. Carefully remove spool from valve body. NOTE—Spool
and sleeve are a matched set. Care should be taken not to
mix different valve parts.
4. 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.) Inspect the o-rings on sleeve. If
they are badly worn or defective, they should be replaced
using the Valve Rebuild Kit (part #MC44I-707).
5. The spool and sleeve can be cleaned using a spray-on
evaporative electro-contact cleaner; e.g. ENVI•RO•TECH™
1677, or cleaned with a detergent powder; e.g.
ALCONOX®. If using these cleaners, follow manufacturer's
instructions carefully. DO NOT USE ANY TYPE OF
CLEANER THAT IS ABRASIVE OR LEAVES A RESIDUE.
6. Rinse the spool and sleeve thoroughly and dry with a soft,
clean, lint-free cloth.
7. Ensure that the air passages (ports) in both the valve body
and manifold are free of any foreign matter.A clean, lint-free
cloth or a compressed air hose can be used to clean these.
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