DeVilbiss 525DS - TROUBLESHOOTING

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LT-2023

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 17.

The compressed air passes through a rotary 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 rotary valve assembly. The ports are connected to a single piece of hose running from

the valve to the exhaust mufﬂer.

Also during each bed pressurization, a small amount of oxygen ﬂows through an oriﬁce (Figure 6) 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 10), 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 voltage to the valve

causing it to shift and alternately pressurize the sieve beds.

The PC board also activates the electronic alert 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. Low ﬂow, system abnormality, and power failure are indicated by audible and visible

alerts.

The 525 Model operating system incorporates “turn-down” technology. The PC board constantly monitors the ﬂow rate and will decrease the cycle

time whenever the ﬂow rate is less than 2.5 LPM. Therefore it “turns-down” the cycle based on lower oxygen demand. As a result, the unit runs cooler

and less power is consumed.

NORMAL OPERATING SEQUENCE

When the concentrator is turned “On,” the following cycling sequence can be observed by attaching pressure gauges to the sieve bed test points.

1. The rotary valve is quickly cycled several times to relieve residual bed pressure preventing a static condition in the compressor. This rapid cycling

only happens on start-up and is clearly heard as pressure is being quickly exhausted several times through the exhaust mufﬂer that is connected to

the valve.

2. The PC board applies a short DC voltage signal to the valve. The valve will stop for several seconds causing the right bed to pressurize ﬁrst while

the left bed depressurizes to approximately 2 PSI (14 kPa).

3. Voltage is again applied to the valve for a short time. The valve will stop for approximately a second. During this time the sieve bed pressures are

equalized.

4. A short DC voltage signal is again applied to the valve. The valve will stop for several seconds causing the left bed to pressurize while the right bed

depressurizes to approximately 2 PSI (14 kPa).