Purge Rate Pressure – Models 590 To 5400; Alarms; Purge Pressure Setting; Tower Status Leds - Gardner Denver DGH Series Instruction Manual

8.1.4.2 Purge Rate Pressure – Models 590 to 5400
•
Refer to Table 8-4 for the proper purge rate pressure
setting corresponding to the conditions listed in Section
8.1.4. Note: For units with the Level 2 Controller and
the Automatic Purge Saving System in the demand
cycle mode use the ISO Class 2 (10 min.) purge
pressure settings only.
•
Adjust purge rate valve until purge pressure gauge
indicates the required pressure. The purge pressure
adjustment valve on Models 590 through 5400 is a globe
valve located in the smaller by-pass line of the upper
piping in the front of the dryer. Refer to Figure 4-3.
IMPORTANT: Adjustment must be made while either
tower is purging (air exhausting from muffler).
•
The purge pressure adjustment valve should never be
fully closed. Proper purge flow is required to regenerate
and re-pressurize the offline tower. Should the tower fail
to re-pressurize, a switching failure alarm will be initiated,
and the cycle will be stopped before tower switch over.
•
After the purge pressure has been correctly set, the
handle of the purge pressure adjustment valve may be
removed and stored to prevent tampering with the setting.
Insufficient purge air will eventually result in saturation of the
desiccant beds and wet air downstream. Verify that maximum
operating pressure mode, cycle time, energy (purge) savings
percent selection, and purge pressure are correctly set.
8.1.5 Bringing the Dryer Online
Establish a normal flow through the dryer. Slowly open the
outlet isolation valve if present. Close any dryer by-pass valves.
NOTE: When dew points below -40°F (-40°C) are required, the
dryer must be run with an inlet flow rate of less than 50% of
maximum until the desired dew point is attained. Depending on
the initial dryness of the desiccant, this can take as long as 2 to
3 days. This stabilization period is required on initial startup,
after the dryer has been shutdown for extended periods of time,
or after dryer maintenance (desiccant change, etc.) has been
performed.
8.1.6 Readjusting the Purge Rate
With the inlet pressure to the dryer at its minimum level,
readjust the purge pressure per the instructions in Section
8.1.4.
NOTE: Adjustment must be made while the appropriate tower is
purging (air exhausting from muffler).
8.2 Operational Check Points
8.2.1 Power to unit
Check periodically that there is power to the unit (indicating
lights illuminated).
8.2.2 Moisture Indicator
8. Operation
Every four hours check moisture indicator. Indicator should be
green. The color change moisture indicator indicates the outlet
relative humidity of the desiccant dryer.
Green indicates a R.H. below 3% and yellow indicates a R.H.
above 3%. Table 8-5 cross references outlet pressure dew
points to moisture indicator changes from green to yellow at
various inlet temperatures.
NOTE: During start-up the indicator may be yellow, however, it
should begin to change to green within four hours.

8.2.3 Purge Pressure Setting

Every four hours check the purge pressure gauge for the proper
setting and adjust as required. Adjustment should be made
when the inlet pressure to the dryer is at its minimum level.
NOTE: Adjustment must be made while the appropriate tower is
purging (air exhausting from muffler).

8.2.4 Alarms

Periodically check for flashing red alarm LED.
8.2.4.1 Alarms – Level 1 Controller
Alarm light will flash if either tower fails to pressurize or de-
pressurize to the required levels at the proper time. Refer to
Section 6.4.3 and Table 6.6.
NOTE: Alarm will activate if dryer is energized without being
pressurized. If this occurs, allow dryer to cycle to next step and
press reset button. Alarm light will continue to illuminate even if
fault clears. To clear alarm, press reset button.
If the tower being regenerated fails to re-pressurize, the dryer
will not switch towers. The switching failure alarm will be
activated and the dryer will remain in this mode until the tower
re-pressurizes.

8.2.5 Tower Status LEDs

Illuminated LEDs indicate which tower is on-line drying or off-
line regenerating.
8.2.6 Tower Pressure Gauges
Periodically check tower pressure gauges to verify that the
pressure gauge of the online tower reads line pressure and the
pressure gauge of the offline tower reads below 2 psig (0.14
kgf/ cm .
2)
NOTE: Read the offline tower pressure gauge when the tower
is purging (air exhausting from muffler).
8.2.7 Check Mufflers For Backpressure
Excessive backpressure may result due to the accumulation of
desiccant fines (dust) in the muffler cartridges. This sometimes
occurs after start-up due to dusting of the desiccant during
tower filling and dryer transport. If the tower pressure gauge of
the off-stream tower rises above 5 psig (3.5 kgf/ cm
muffler elements should be replaced.
8.2.8 Process Valves
Determine if air control valves are operating and sequencing
correctly.
Refer to Section 3.3 for a general description of operating
sequence. Refer to Tables 6-3 and 6-4 for time sequences for
- 46 –
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