SPX Hankinson HHE Series Instruction Manual page 7

3.3.3 Models 40 to 450 (High Pressure Option)
(Refer to Fig. 3-3a.) Compressed air flows through inlet switching
valve (3A) (normally open) to tower (4A) where the air is dried. After
the air is dried it flows through shuttle valve (5) and then to the dryer
outlet. A portion of the dry air, the purge stream, branches off from
the main air stream prior to the outlet. The purge stream flow rate is
controlled by the adjustable purge rate valve (6) and the two purge
orifices (7).
The purge flow, which has been throttled to near atmospheric pressure,
is directed to tower (4B). As the purge flow passes over the desiccant
in tower (4B), it removes the water vapor which was deposited while
the tower was on-line drying. The purge air then passes through
purge and repressurization valve (9B) (normally closed) and purge
muffler (10B) to the atmosphere.
After regeneration, purge and repressurization valve (9B) (normally
closed) closes allowing tower (4B) to re-pressurize slowly. Adequate
repressurization time is allowed so that tower (4B) is fully re-
pressurized before switchover. After a controlled time period, air
inlet switching valve (3B) (normally open) opens and inlet-switching
valve (3A) (normally open) closes, purge and repressurization
valve (9A) (normally closed) then opens.
(Refer to Fig. 3-3b.) Tower (4B) is now drying the main air stream while
tower (4A) is being regenerated by the purge air stream. The operation
of the inlet switching (normally open) and purge and repressurization
(normally closed) valves is sequenced by the control system located
in the electrical enclosure.
TOWER
4A
TOWER
4A
1. Tower Pressure Gauges
2. Purge Pressure Gauge
3. Inlet Switching Valves
4. Desiccant Drying Towers
5. Shuttle Valve
6. Adjustable Purge Rate Valve
7. Purge Orifices
Process Stream
Purge Stream
— 5 —
OUTLET
11
5
1 1
8
7 7
6 2
TOWER
3A 3B
9A 9B
INLET
10A 10B
FIGURE 3-3a
TOWER 4A DRYING
TOWER 4B REGENERATING
OUTLET
11
5
1 1
8
7 7
6 2
TOWER
4B
3A 3B
9A 9B
INLET
10A 10B
FIGURE 3-3b
TOWER 4A REGENERATING
TOWER 4B DRYING
8. Safety Valve
9. Purge and Repres-
surization Valves
10. Purge Mufflers
11. Moisture Indicator
A Left Tower Suffix
B Right Tower Suffix
4B