10
TROUBLESHOOTING
SYSTEM OPERATION
The DeVilbiss Oxygen Concentrator uses a pressure swing
adsorption system.The air is drawn into the unit through air
filters and into a double-head compressor.
A pneumatic diagram of the system is shown in Figure
15.
The compressed air passes through a four-way valve (Figure 5),
which is cycled at a pre-determined rate, and is directed into
one of two sieve beds.The sieve beds contain molecular sieve
material which is a synthetically-produced inorganic silicate. It is
very porous and has the unique ability to selectively adsorb
nitrogen from the air as it passes through the sieve bed.
As one bed is being pressurized, the other bed is quickly
depressurized.This allows the nitrogen that was adsorbed
during its pressurization cycle to be exhausted from the
sieve material.
The nitrogen is released through exhaust ports located on the
four-way valve assembly.The ports are connected to a single
piece of black hose running from the valve to the exhaust muffler.
Also during each bed pressurization, a small amount of oxygen
flows through an orifice (Figure 9) from the pressurized bed
into the depressurizing bed.The orifice is clamped inside a long
piece of blue tubing connecting the outlets of the two sieve
beds.This helps purge the nitrogen from the depressurizing bed.
The beds will continue to be alternately pressurized and
depressurized as the unit operates.
Oxygen leaving the sieve beds is directed through a check
valve to the accumulator tank.A pressure regulator (Figure 9)
on the tank controls the oxygen pressure as it leaves the
accumulator and enters the flow meter.The flow meter allows
the oxygen flow to be controlled and adjusted to the level
prescribed by the patient’s physician. From the flow meter the
oxygen passes through the final bacteria filter (Figure 8), a
check valve, and finally the oxygen outlet port to the patient.
The DeVilbiss Oxygen Concentrator operates on a timed
cycle.The cycling is controlled by the PC board.The PC board
will send approximately 7.5 VDC (
12-15 VDC on non-OSD
and early-OSD models) to the four-way valve causing one of
the two solenoids to energize.
The PC board also activates the electronic alarm system.A
high pressure condition will be indicated with a “popping” type
sound produced by release of pressure from a pressure relief
valve on the compressor head.
NORMAL OPERATING SEQUENCE
When the concentrator is turned “On,” the following normal
cycling sequence should be observed by attaching pressure
gauges to the sieve bed test points.
1. The four-way valve is quickly cycled back and forth several times
to relieve residual bed pressure preventing a static condition in
the compressor.This rapid cycling only happens on start-up.
NOTE: The rapid cycling will be heard as several thumping
noises at start-up.
2. An approximately 7.5 VDC (
12-15 VDC on non-OSD and
early-OSD models) signal from the PC board is supplied to
the right solenoid for approximately 9-
10 seconds.The left
sieve bed pressurizes while the right sieve bed is being depres-
surized to approximately 2 PSI (
14 kPa).
3. The signal is then removed from the right solenoid. No voltage
is applied to either solenoid for approximately
1 second. Both
sieve beds are being equalized in pressure during this phase.
4. An approximately 7.5 VDC (
12-15 VDC on non-OSD and
early-OSD models) signal from the PC board is applied to the
left solenoid for approximately 9-
10 seconds.The right sieve
bed pressurizes while the left sieve bed is depressurized to
approximately 2 PSI (
14 kPa).
5. The signal is then removed from the left solenoid. No voltage
is applied to either solenoid for approximately
1 second. Both
sieve beds are being equalized in pressure during this phase.
6. The cycle then repeats with step 2.
NOTE: High-end sieve bed pressure should not exceed 1/2
PSI (4 kPa) above high-end accumulator pressures. Refer to
“Specifications” for normal pressures obtained during the cycle.
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