Gardner Denver DGH Series Instruction Manual page 6

3. Description
3.4 Automatic Purge Saving System
(Refer to Figure 3-3a for Models 40 through 450 and Figure
3-3b for Models 590 through 5400.)
Assume tower A is on-line drying while tower B has just gone off-
line to be regenerated. At the beginning of tower B's
regeneration cycle a thermistor temperature measurement is
made at position B1. After the tower has been regenerated,
another measurement is made at B1. The drop in temperature
sensed during regeneration is an indirect measure of the water
vapor content of the inlet air. The Automatic Purge Saving
System's microprocessor then uses this information to calculate
an allowable temperature rise in the bed during the drying cycle.
When tower B goes back on-line, a temperature probe at
position B2 measures the initial bed temperature at this point
and then monitors the bed until the calculated temperature rise
occurs. The temperature rise occurs as heat of adsorption is
released during the drying process. The time for the temperature
rise to occur depends on flow rate. At 100% flow the temperature
rise takes 5 minutes, at 50% flow it takes 10 minutes.
NOTE: If after 30 minutes, the bed temperature has not risen
to the calculated value, the dryer will automatically switch
towers.
When the calculated temperature rise is reached, the towers
switch with tower A now drying and tower B being regenerated.
Tower B regenerates for 3.9 minutes, re-pressurizes, and
remains idle until it is called upon for the next drying cycle.
3. Description
TOWER
4A
9A
10A
1. Tower Pressure Gauges
2. Purge Pressure Gauge
3. Inlet Switching Valves
4. Desiccant Drying Towers
5. Shuttle or Check Valve(s)
6. Adjustable Purge Rate Valve
7. Purge Orifice(s)
Process Stream
Purge Stream
- 6 –
OUTLET
11
5
1 1
8
7 7
6 2
A2 B2
TOWER
A1 B1
3A 3B
9A 9B
INLET
10A 10B
FIGURE 3-3a
Models 40 through 450
TOWER 4A DRYING
TOWER 4B REGENERATING
OUTLET
5A 5B
8 8
11
6
2 5D
5C
1 1
7
A2 B2
TOWER TOWER
4A 4B
A1 B1
3A 3B 9B
INLET
FIGURE 3-3b
Models 590 through 5400
TOWER 4A DRYING
TOWER 4B REGENERATING
8. Safety Valve(s)
9. Purge and Repres-
surization Valves
10. Purge Mufflers
11. Moisture Indicator
A & C Left Tower Suffix(es)
B & D Right Tower Suffix(es)
4B
10B