Compu-Purge Control; Automatic Drain Valve (Adv); Start-Up - Ingersoll Rand HRD Serie Manuel De Instrucciones

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.
At the end of the drying period, exhaust valve D
opens, vessel A depressurizes, inlet and outlet shuttle
valves shift, inlet flow switches to vessel B and the
drying/regenerating cycle is repeated.
For standard models designed to provide a –40°F pres-
sure dew point, inlet air continues to flow through one
vessel for half of the standard 10-minute cycle. For
models designed to provide a –100°F pressure dew
point, the standard cycle is 5 minutes.

Compu-Purge Control

Compu-Purge control uses a microcomputer to adjust
the purge airflow rate and drying cycle to automati-
cally match purge air to the inlet moisture load.
Electronic temperature and pressure sensors continu-
ously track inlet temperature and inlet and outlet pres-
sure and transmit these to the microcomputer. The
microcomputer calculates the dryer load and the most
efficient combination of purge flow rate and duration
to regenerate the moisture adsorbed during the drying
period.
Purge flow rate can be varied from 0 to 20% in incre-
ments of 5% by purge control valves 1 and 2. Purge
duration can also be varied. The optimum combination
of purge control valve openings is automatically se-
lected by the microcomputer to supply only as much
purge air as needed for complete regeneration.
When the amount of purge air required to regenerate
the desiccant is more than 20% of the inlet flow, the
dryer will operate on a shortened cycle until the over-
load condition is corrected. For models designed to de-
liver air at –40°F pressure dew point, the dryer will
operate on a 5-minute cycle when in the Overload
Mode. For –100°F pressure dew point operation, a
3-minute cycle is used.
The microcomputer uses three modes of dryer opera-
tion to match the inlet moisture load:
• Compu-Purge Mode – When the microcom-
puter adjusts purge air to match dryer load re-
quirements, the dryer is operating in the
Compu-Purge mode.
• Standby Mode – When there is low or no de-
mand for air, the dryer operates in a standby
mode: the dryer purges until the desiccant is re-
HRD Series (Bulletin 348)
generated, the vessels repressurize, then the
dryer automatically shuts down; the dryer
purges every 30 minutes to assure dew point
performance.
• Fixed-Cycle Mode – If all sensors malfunction,
the "Variable Purge Mode" light will turn off
and the dryer will automatically operate in a
fixed cycle mode, using 15% of the design air-
flow to regenerate the offstream vessel. If only
one sensor malfunctions, the dryer will default
to standard conditions for that sensor and con-
tinue to operate in the Variable Purge Mode.
See Maintenance section, page 1-10, for addi-
tional information.

AUTOMATIC DRAIN VALVE (ADV)

Dryer models HRD200 and larger are equipped with
an electronic drain valve that automatically discharges
condensate from the prefilter.
The ADV has two LED indicators and a test button to
help verify operation. Pushing the test button causes
the drain port to click open. One LED indicates that
power is supplied to the ADV; the other LED indicates
that the drain port is open. The power indicator turns
off when the drain port opens. If either LED fails to
turn on at the proper time, refer to the maintenance
section of this manual. If the dryer is under warranty,
call your local distributor for authorization before
servicing.
ADV operation is controlled by an electronic timer.
The drain opening can be set from 0.5 to 10 sec. The
drain cycle can be set from 0.5 to 45 min.
To minimize air losses, the timer should be adjusted to
open the port just long enough to discharge accumu-
lated condensate. The timer is properly set if nothing
but air vents at the end of the open period. If air vents
for more than a few seconds, set the timer for a longer
cycle or shorter drain opening. If liquid is still dis-
charging when the port closes, set the timer for a
shorter cycle or longer drain opening.

START-UP

Once your HRD Series dryer has been installed ac-
cording to instructions, it is ready for start-up.
To start the dryer:
1. Close customer-supplied shutoff valve at dryer in-
let.
2. Open customer-supplied bypass valve, if installed.
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