DESCRIPTION
®SULLAIR®
3700 Operator’s Manual and Parts List
13
The integrated inlet valve has an orifice which vents a
small amount of air inlet when the pressure regulator
controls the inlet control valve. The orifice also bleeds
any accumulated moisture from the control lines.
UNLOAD MODE - IN EXCESS OF 110 PSIG
(7.6 BAR)
When a relatively small amount or no air is being used,
the service line pressure continues to rise. When it
exceeds 110 psig (7.6 bar), the microprocessor control
system de-energizes the solenoid valve allowing sump
air pressure to be supplied directly to close the inlet
valve. Simultaneously, the solenoid valve sends a
pneumatic signal to the blowdown valve. The blowdown
valve opens to the atmosphere, located in the
compressor intake, reducing the sump pressure to
approximately 17 psig (1.2 bar). The check valve in the
air service line prevents line pressure from returning to
the sump.
When the line pressure drops to the low setting (cut-in
pressure; usually 100 psig (6.9 bar) on low pressure
(7 bar) compressors and 125 psig (8.6 bar) on high
pressure (9 bar) compressors, 150 psig (10.3 bar) on (10
bar) compressors, 175 psig (12.0 bar) (12 bar), the
microprocessor controller energizes the solenoid valve
and allows the blowdown valve to close. The re-
energized solenoid valve again prevents line pressure
from reaching the inlet control valve. Should the
pressure begin to rise, the pressure regulator will
resume its normal function as previously described.
LOAD/NO LOAD CONTROL
If desired by the customer, the compressor can be set to
operate load/no load without modulating control. This
control mode is often selected when a large amount of
compressed air storage (air tank) is available. Using the
microprocessor keypad, select “load/no load control”
from the menu. On a machine rated for 100 psig (7 bar)
the compressor will run in the full load mode up to
100 psig (7 bar). If less than the rated capacity is
required, pressure will rise above 100 psig and the
microprocessor will de-energize the solenoid valve,
causing the compressor to run in the unload mode.
When the system pressure falls to 90 psig (6.3 bar), the
microprocessor energizes the solenoid valve, causing
the compressor to return to the full load mode. The
compressor will thus operate to keep the system
pressure in the range of 90-100 psig (6.3 - 6.9 bar).
AUTOMATIC OPERATION
For applications with varied periods of time when there
are no air requirements, the microprocessor’s
AUTOMATIC mode allows the compressor to shutdown
(time delayed) when no compressed air requirement is
present and restart as compressed air is needed.
2.7 AIR INLET SYSTEM, FUNCTIONAL
DESCRIPTION
Refer to Figure 2-5. The Compressor Inlet System
consists of a dry-type air filter, a restriction gauge
and an air inlet valve.
The restriction gauge (located on the air filter) indicates
the condition of the air filter by showing red when filter
maintenance is required.
The poppet-type modulating air inlet valve directly
controls the amount of air intake to the compressor in
response to the operation of the pressure regulator (see
MODULATING MODE - 100 TO 110 PSIG (6.9 TO 7.6
BAR) on page 12). The inlet valve also acts as a check
valve, thus preventing reverse rotation when the
compressor is shut down.
A WARNINGA WARNINGA WARNING
“The Plastic Pipe Institute recommends
against the use of thermoplastic pipe to
transport compressed air or other
compressed gases in exposed above
ground locations, e.g. in exposed plant
piping.” (I)
Sullube should not be used with PVC
piping systems. It may affect the bond at
cemented joints. Certain other plastic
materials may also be affected.
(I) Plastic Pipe Institute, Recommendation
B, Adopted January 19, 1972.
SU_0000024
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