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06712B (DCN5875)
5-1
5 OPERATION
5.1 Overview
Refer to Figure 5-1, and Figure 5-2.
The M701H dries and scrubs ambient air to produce zero air.
The compressor draws air in from the rear panel bulkhead union and inlet filter. At the
compressor outlet, the air is under pressure and hot from the compression. The relative
humidity is high as a result of the high pressure.
The air is conducted through the cooling coil where heat is removed by transfer to the
cooling fan air. With the high pressure and the temperature reduced to ambient level,
the relative humidity is at its highest. At this point, the air is usually supersaturated.
From the coil, the wet air passes through a coalescing filter where the excess water is
separated and settles in the bottom of the filter. The controller periodically opens the
solenoid drain valve allowing the water to be expelled through a rear panel bulkhead
union (drain).
The partially dried air enters the Regenerative Dryer which removes essentially all the
remaining water and a portion of the other contaminants. The pressure relief valve may
open occasionally and can be loud but this is a normal part of the operation for the
M701H.
The dry air then passes through a check-valve to the storage tank. A pressure switch
turns off the compressor when the pressure in the tank reaches a set high value, and
turns the compressor on when the pressure reaches a set low value. Thus, when air
demand is low, the compressor is turned off and the tank fulfills the demand. The
pressure in the tank varies from approximately 45 psig to approximately 80 psig
depending on the demand and the restricted output. Some special calibrators with
restricted output are set to 50 psig. As the air leaves the tank, its pressure is controlled
to 30 psig by an air pressure regulator mounted on the front panel. This maintains a
constant pressure at the calibrator inlet and is displayed by the pressure gauge on the
M701H front panel.
For a final clean-up, the dry, regulated air enters the specific scrubbers as follows:
1. The Hydrocarbon scrubber where Hydrocarbons and CO are catalytically converted
to CO
2
and water.