Teledyne 751H 4 OPERATION

07773A DCN6833 19

4 OPERATION

Refer to Figure 4-1 for a diagram of the 751H pneumatic flow.

The 751H dries and scrubs ambient air to produce zero air. To accomplish this, first

the compressor draws air in through the intake filter and compresses it. 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 h igh 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 drain fitting.

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 751H.

As the air leaves the dryer, its pressure is controlled to 30 psig by an air pressu re

regulator mounted on the instrument panel. This maintains a constant pressure at the

calibrator inlet and is displayed by the pressure gauge on the 751H instrument panel.

For a final clean-up, the dry, regulated air enters the specific scrubbers/filters as

follows:

1. The Hydrocarbon scrubber where Hydrocarbons are catalytically converted to

CO2 and water.

2. The NO scrubber where NO is oxidized to NO2.

3. The activated charcoal scrubber where the NO2, O3, SO2 and H2S are absorbed.

4. The CO scrubber, where CO is catalytically oxidized to CO2.

5. The clean dry air passes through a fine particulate filter and leaves the 751H

through the instrument panel bulkhead union (Zero Air Out).