SPX Hankinson HHE Series Instruction Manual page 5

3.3 Description of Operation – Dryer
3.3.1 Models 40 to 3000 w/ Shuttle Valve
(Refer to Fig. 3-1a.) Compressed air flows through inlet shuttle valve (3)
to tower (4A) where the air is dried. After the air is dried it flows through
outlet 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 there
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 repressurize slowly. Adequate
repressurization time is allowed so that tower (4B) is fully repressurized
before tower switchover. After a controlled time period, purge and
repressurization valve (9A) (normally closed) then opens. This causes
the inlet and outlet shuttle valves to shift, directing the air flow through
tower (4B).
(Refer to Fig. 3-1b.) Tower (4B) is now drying the main air stream
while tower (4A) is being regenerated by the purge air stream. The
operation of the 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 Shuttle Valve
4. Desiccant Drying Towers
5. Outlet Shuttle Valve
6. Adjustable Purge Rate Valve
7. Purge Orifices
Process Stream
Purge Stream
— 3 —
OUTLET
11
5
1 1
8
7 7
6 2
TOWER
3
9A 9B
INLET
10A 10B
FIGURE 3-1a
TOWER 4A DRYING
TOWER 4B REGENERATING
OUTLET
11
5
1 1
8
7 7
6 2
TOWER
4B
3
9A 9B
INLET
10A 10B
FIGURE 3-1b
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