SPX Hankinson HHE Series Instruction Manual page 6

3.3.2 Models 4100 to 5400 w/ Check Valves
(Refer to Fig. 3-2a.) 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 outlet check valve (5A) 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 single
purge orifice (7).
The purge flow, which has been throttled to near atmospheric pressure,
is directed through purge check valve (5D) 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. 3-2b.) 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
9A
10A
8
1
TOWER
9A
10A
1. Tower Pressure Gauges
2. Purge Pressure Gauge
3. Inlet Switching Valves
4. Desiccant Drying Towers
5. Check Valves
6. Adjustable Purge Rate Valve
7. Purge Orifice
Process Stream
Purge Stream
— 4 —
OUTLET
5A
5B
8 8
11
6
2
5C 5D
1 1
7
TOWER
4A 4B
3A 3B 9B
INLET
FIGURE 3-2a
TOWER 4A DRYING
TOWER 4B REGENERATING
OUTLET
5A 5B
8
11
6
2
5C 5D
1
7
TOWER
4A 4B
3A 3B 9B
INLET
FIGURE 3-2b
TOWER 4A REGENERATING
TOWER 4B DRYING
8. Safety Valves
9. Purge and Repres-
surization Valves
10. Purge Mufflers
11. Moisture Indicator
A & C Left Tower Suffixes
B & D Right Tower Suffixes
10B
10B