Sunrise Medical DeVilbiss 505DZ Service Manual page 42

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
The four-way valve, while operating pneumatically, uses an external pilot valve that allows pressure to shift the spool inside the four-
way.This pilot valve receives a signal (12-15 VDC) from the PC board causing it to open and allowing pilot pressure to activate the
four-way.When the four-way is activated, the left sieve bed will pressurize. Once the bed fills the oxygen accumulator tank, the cycle
is changed by removing the signal to the pilot valve.This will cause the four-way to deactivate and pressurize the right sieve bed.
NOTE—The four-way valve will not shift until the oxygen accumulator tank is filled.This will take approximately 10 seconds depend-
ing on altitude and liter flow.
If the four-way does not shift, the alarm system may be activated and the short cycle light on the PC board will illuminate. Refer to
Alarm System. If the alarm system is not activated, short cycle times and low oxygen concentration will result because the same bed
will continue to pressurize.
There are several reasons for the four-way to malfunction.The cause of failure must be determined before corrective action can be
taken.
Some reasons for four-way failure are:
• Continuous or no voltage to pilot valve on four-way.
• Little or no pilot pressure.
• Foreign matter inside valve preventing spool from shifting.
• O-rings on sleeve may be worn preventing the valve from shifting properly.
To test four-way 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 "4-way" on the PC board.When this light is illuminated the four-way
should be activated and the left sieve bed should be pressurizing. If the right bed pressurizes instead, this indicates that the four-
way did not properly shift.
Vacuum
pressure
gauge
Pressure
test
assembly
Manifold
base
Left sieve
bed
Figure 38
Oxygen sensor
assembly
(OSD units only)
Vacuum
pressure
gauge
Pressure
Green
test
four-way
assembly
and purge
indicator
lights
Right
sieve bed
42
PC board
Figure 39