How It Works (Hrd-Em Series) - Sigma HRD Serie Manual De Instrucciones

Figure 3
AIRFLOW SCHEMATIC (HRD Series)
A portion of the dried air (purge air) is metered
through orifice C and reduced to atmospheric pressure
by orifice D, greatly expanding its volume. The ex-
panded purge air flows down through vessel B and out
through the purge valve F and muffler, carrying away
moisture adsorbed by the desiccant in the previous cy-
cle.
The dryer operates this way for approximately four
minutes. Then purge valve F closes, allowing vessel B
to gradually repressurize for approximately one minute
before the cycle changes. The cycle timing sequence
will vary depending on operating pressure. At
switchover, purge valve E opens to depressurize vessel
A. This causes shuttle valves S and T to shift so that
vessel B is onstream and vessel A is being reactivated.

HOW IT WORKS (HRD-EM SERIES)

Figure 4 shows the airflow through the dryer with ves-
sel A drying and vessel B regenerating.
Saturated air enters the prefilter which separates oil
mists, liquid oil, water and particulates from the
1-8
Figure 4
AIR FLOW SCHEMATIC (HRD-EM Series)
airstream. Separated contaminants are discharged
through the prefilter drain. With exhaust valve C open
and D closed, filtered air enters the inlet shuttle valve
and is directed through vessel A, where moisture is ad-
sorbed by the desiccant. Dry air exits the vessel, passes
through the outlet shuttle valve and divides into two
streams. The process air passes through the particulate
afterfilter and continues to the process.
A portion of the dried air passes through the purge ori-
fice at approximately atmospheric pressure and passes
downward through vessel B, where it desorbs moisture
from the desiccant. Wet purge air exhausts to the at-
mosphere through exhaust valve C and muffler E.
When regeneration is complete, exhaust valve C closes
and vessel B is repressurized to dryer operating pres-
sure. Vessel B is completely regenerated and
repressurized, ready for the next drying cycle.
HRD and HRD-EM Series (Bulletin 378)