Control And Instrumentation - Domnick Hunter PNEUDRI DX102 Manuel D'installation, De Mise En Service Et D'entretien

3. CONTROL AND INSTRUMENTATION (see Figures 1 & 2)
A) OPERATION
The operation of both Heatless DX models and Heat Regenerative DH models is essentially the same.
A hinged INSTRUMENTATION SHROUD (1) contains the control circuitry, the purpose of which is to provide a fixed
time cycle between the adsorbing and regenerating desiccant beds, and to provide automatic changeover at the end
of each half cycle.
On Heat Regenerative DH models, this also controls the energising of the internal heaters (13).
Filtered compressed air enters through the INLET ASSEMBLY (2) and is directed by the inlet valves into one of the
chambers of the lower manifold (either column A or B). Air from the lower manifold flows upwards, equally through the
dryer columns filled with MOLECULAR SIEVE DESICCANT MATERIAL (3). The desiccant material adsorbs the
moisture contained within the air flow.
The now dried air then enters the UPPER MANIFOLD (4) and exits the dryer through the OUTLET ASSEMBLY (5). A
simple check valve housed within the outlet assembly prevents the dried air passing through the opposite
regenerating bed to atmosphere.
An ADJUSTABLE ORIFICE (6) located on the UPPER MANIFOLD (4), allows a small amount of dried purge air to
flow downwards through the off-line desiccant bed for regeneration. The amount of purge air required is dependent
upon the regeneration principle used. i.e. PSA or TSA.
The regeneration air now contains desorbed moisture when it enters the LOWER MANIFOLD (7) and exhausts to
atmosphere via two exhaust silencers located on the EXHAUST ASSEMBLY (8) in the lower part of the hinged
INSTRUMENTATION SHROUD (1).
Cycling is continuous and automatic, with instrumentation located on the hinged INSTRUMENTATION SHROUD (1)
giving a visual indication of the dryer operation at all times.
Pressure gauges are provided to indicate:
COLUMN 'A' PRESSURE (9), INLET PRESSURE (10) AND COLUMN 'B' PRESSURE (11).
Outlet pressure is the same as the column pressure. During the normal operation of the dryer one column will be
drying the incoming air and the opposite column will be undergoing regeneration. This can be identified by checking
column pressure gauges. The adsorbing column will be pressurised whilst the regenerating column is at atmospheric
pressure.
During the dryers' cycle, the control circuit will signal the exhaust valves to close, to allow the regenerating column to
reach line pressure before changeover. At this time both column pressure gauges will indicate line pressure.
The dryer cycle will then proceed to change over, allowing the fully regenerated bed to dry the incoming compressed
air.
During normal operation the cobalt chloride paper within the MOISTURE INDICATOR (12) will be a blue/green colour.
Should a system or dryer malfunction occur the paper will gradually change colour to amber (see fault diagnosis
section).
Should this occur, the fault should be identified and rectified before the paper in the moisture indicator is replaced.
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