DeVilbiss DeVO/MC44-90 - Manifold Check Valves; Molecular Sieve Bed Assemblies

SECTION 7
SERVICE INSTRUCTIONS
If a manifold check valve is determined to be
faulty, the manifold base must be replaced.
Refer to section K for manifold assembly
replacement.
A third check valve (1 Fig. 12) is located
between the final bacteria filter and the
oxygen outlet fitting. This check valve allows
oxygen to flow in only one direction and
prevents gas or water from being drawn back
into the unit. When unit is turned off this
check valve allows accumulator tank to drain
completely.
A defective final check valve may cause water
to be drawn in from the humidifier bottle
when unit is turned off. This may occlude the
final bacteria filter and/or the flow meter
causing a restriction of flow and making it
difficult to adjust the flow rate.
To replace final check valve:
1. Unplug unit from wall outlet.
2. Refer to Service Instruction B to open
front cover.
3. Remove hose clamp and hose from each
end of check valve.
4. Attach hoses to new check valve ensuring
that the end of the check valve labeled
VAC is directed toward the oxygen outlet
fitting. Secure with hose clamps.
5. Close front cover and secure with cabinet
fasteners.
Molecular Sieve Bed Assemblies
The two molecular sieve beds (1,2 Fig. 10) al-
ternately remove the nitrogen from the air
passing through them and provide the
patient with a constant supply of oxygen.
Sieve bed pressures can be read by attaching
pressure gauges to the test points (1 Fig. 22)
located on manifold assembly. Normal bed
pressures are approximately 26 PSI (179 KPa)
when taken at these test points or access
fittings. Pressures will be approximately 1-2
PSI (6.9 - 13.8 KPa) when bed is depressurized.
The efficiency of the molecular sieve material
will be impaired if it becomes contaminated
by moisture. Contamination causes the
molecular sieve materia! to lose its nitrogen
adsorbing properties resulting in a reduction
in oxygen concentration. Also, the pressure
within the sieve bed will increase faster
because of contamination which results in a
shorter cycle time. Cycle time will continue to
15
decrease as bed contamination becomes more
severe. Concentrations will also continue to
decrease. Once the cycle time reaches the
minimum pre-set cycle time the short and no
cycle alarms will be activated.
To test sieve beds:
Tools needed:
(2) Pressure gauges (Part #444-591)
(2) Pressure test assembly (Part #444-502)
1. Remove the plugs from the two access
fittings (6,11 Fig. 16) located at the top
corners of the manifold.
2. Attach the 1/16” 1.D. hose from the test
assembly to one of the access fittings on
the manifold. Then attach one of the
plugs to the barb fitting on the test
assembly. Attach the second pressure test
assembly to the other access fitting in the
same manner and then connect the
pressure gauges to the test assemblies (4,7
Fig. 22).
3. Turn the unit on and observe the cycling
(see Figure 22). Normal cycle times are
approximately 16 seconds at 2 LPM, but
this will vary slightly depending on
altitude and the liter flow setting. Refer
to the normal cycling sequence on page
24.
4. Check oxygen concentration of unit.
A combination of short cycle times and
low oxygen concentrations indicate con-
taminated sieve beds.
NOTE: If the short and no cycle alarms have
been activated it must be determined wheth-
er the problem is with the sieve bed or a
failure of the four-way valve to shift. This is
done by observing the cycling or noncycling
of the unit. Short cycling would indicate bed
failure and noncycling would indicate a four-
way valve malfunction.
If the molecular sieve material is found to be
no longer effective, first locate the source of
the malfunction or cause (such as leaks) for
contamination and take corrective actions.
To replace the molecular sieve beds:
1. Unplug unit from wall outlet.
2. Refer to Service Instruction B to open
cabinet covers.
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