Compu-Purge (Hrd-Em Only); How It Works (Hrd Series) - Sigma HRD Serie Manual De Instrucciones

high-humidity alarm. Contacts for remote annunciators
are connected to the terminal strip in the electrical en-
closure; refer to the electrical schematic for terminal
numbers. Refer to the maintenance section of this
manual for field adjustment instructions.

Compu-Purge (HRD-EM only)

Indicators
HRD-EM Series dryers are equipped with
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Compu-Purge control which has an indicating panel
(Figure 2) on the door of the main electrical box.
These indicators help in monitoring dryer operation
and performance. If the dryer malfunctions, first check
this panel to determine the cause of the problem.
Light
Lights when switch is in "ON" position
Power ON
and power is supplied to dryer.
Variable Purge Lights when drying cycle is controlled
Mode by the microcomputer.
Lights when inlet air temperature ex-
ceeds 120°F. Excessive inlet air tem-
High Inlet Air
perature significantly decreases
Temperature
drying capacity and may result in
higher dew point.
Lights when inlet dryer load exceeds
Dryer Overload
dryer ability to maintain dew point.
Lights when inlet air pressure is less
Low Inlet Air than 65 psig. See Maintenance sec-
Pressure tion (page 1-11) for additional infor-
mation.
Lights when temperature or pressure
sensor sends the microcomputer a
Sensor reading which is outside the normal
Malfunction range of the sensor. See Maintenance
section (page 1-11) for additional in-
formation.
Lights when the high humidity moni-
tor senses excessive moisture in the
High Humidity
outlet air. High humidity may result
when dryer is slugged with water.
Lights if airflow fails to alternate be-
tween desiccant vessels at desig-
Failure-to-Switch nated switching time. Failure to switch
causes desiccant saturation, resulting
in higher dew point.
Liquid Crystal Digital (LCD) Display
The LCD display is above the indicating panel on the
main electrical box. It displays "INLET AIR TEM-
PERATURE" (°F) and "ENERGY SAVINGS" as a
percent of dryer capacity. See Maintenance section,
page 1-11, for complete description of additional read-
outs.
Audible Alarm
Indicates high-humidity and failure-to-switch alarm
condition.
HRD and HRD-EM Series (Bulletin 378)
Function
Figure 2
COMPU-PURGE
Remote Contacts
Powered 120 volt, normally open, contacts (1 amp
max.) are furnished to allow hookup of remote audible
or visible system malfunction alarms. Hookup contacts
are identified by a tag on the bottom center of the elec-
trical box.

HOW IT WORKS (HRD SERIES)

HRD Series heatless dryers provide a continuous sup-
ply of dry compressed air by automatically cycling the
flow of air through two desiccant beds. While one bed
is adsorbing moisture from the inlet air, the other bed
is being reactivated by a portion of the dried air. Cy-
cling is controlled by a cam timer. Figure 3 shows the
airflow through the dryer with vessel A onstream and
vessel B being reactivated.
Saturated air enters the prefilter which separates oil
mists, liquid oil, water and particulates from the air-
stream. Separated contaminants are discharged
through the prefilter drain. With purge valve E closed,
filtered air flows through shuttle valve S into the bot-
tom of vessel A; moisture is removed from the air-
stream by the desiccant. Dry air exits the top of the
vessel and divides into two streams: process air exits
through the shuttle valve T, passes through the particu-
late afterfilter and continues to the process.
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INDICATING PANEL
1-7