Air Inlet System; General Operation Of The Air Inlet System; Air Filter; Inlet Valve - Sullair ShopTek ST18 Operation & Maintenance Manual

2: Description

2.2 Air inlet system

The air inlet system provides air for the compressor to
pressurize. The primary components of the air inlet sys-
tem are the air filter, inlet valve, and compressor air end.
2.2.1 General operation of the air inlet
system
The air end draws outside air through the air filter and
inlet valve into the air end compression chamber. Inside
the compression chamber, a male and female rotor pair
revolve at high speed, compressing the air and increas-
ing its pressure. When the compressed air/fluid mixture
reaches the end of the compression chamber, the mix-
ture flows through the air end discharge port into the
fluid/air separator.
2.2.2

Air filter

The air filter removes particulates from the intake air, pro-
viding clean air to the compressor. If these particulates
were not removed, they could wear down rotor surfaces
and contaminate the compressor fluid.
2.2.2.1 Air filter element
Because the air filter element traps the particulates it fil-
ters from the air on its surface, the air filter element must
be changed periodically to maintain the air filter's effec-
tiveness.
Additional information
• For the recommended air filter maintenance
schedule, see Section 6.3: Recommended
maintenance schedule on page 28.
• For instructions on how to change the air filter
element, see Section 6.4.4: Air filter mainte-
nance on page 30.
WARRANTY NOTICE
Failure to follow the air filter maintenance sched-
ule or use Sullair genuine air filter elements can
cause early contamination of the compressor
fluid and the fluid/air separator element and may
void your warranty.
2.2.3

Inlet valve

The inlet valve controls intake air volume using a modula-
tion control system.
2.2.3.1 Inlet modulation
To minimize the number of starts and stops the compres-
sor makes, the inlet modulation system automatically
12
ST18 & ST22 (U.S.A. & Mexico) Operation & Maintenance Manual
88291013-137 R05
Subject to EAR, ECCN EAR99 and related export control restrictions.
adjusts the size of the inlet valve opening to match air
demand. The primary components of the inlet modulation
system are the solenoid valve, inlet valve, blowdown
valve, and control line.
When air demand is equal to or greater than the com-
pressors rating, the compressor will run at full load. The
solenoid valve is energized, closing the control line.
Because the control is not in use, the inlet valve of the air
end is fully open.
When air demand is lower than the compressor rating,
discharge pressure builds up slowly. Once the discharge
pressure reaches the unload setting of the controller, the
compressor will switch to unload mode. The solenoid
valve is de-energized, opening the control line. Because
the control line is in use and the discharge pressure is
high, the control line closes the inlet valve. At the same
time, the blowdown valve opens to release the pressure
in the fluid/air separator tank until the pressure stabilizes
at 15 – 25 psi.
Now the compressor will run with no load for a preset
time. Once the preset time is reached, the compressor
will stop. However, if the discharge pressure drops to the
load setting of the controller before the preset time is
reached, the compressor re-enters load mode. The sole-
noid valve is energized, closing the control line. Because
the control is not in use, the inlet valve of the air end is
fully open.

2.3 Discharge system

The discharge system pushes air from the compressor
air end to the service connector. The primary compo-
nents of the discharge system are the compressor air
end, fluid/air separator, minimum pressure valve, pres-
sure relief valve, automatic blowdown valve, aftercooler,
moisture separator (optional), and service connector.
2.3.1 General operation of the discharge
system
The compressed air/fluid mixture flows through the air
end discharge port into the fluid/air separator tank and
separator element. The separator tank and element
remove fluid from the air.
The compressed air then flows through the minimum
pressure valve, followed by the aftercooler, then the
moisture separator (if installed). Once the air is cooled
and the moisture removed (if the moisture separator is
installed), the air flows to the service connector for down-
stream use.
To lower the frequency of the compressor's load/unload
cycles and extend the life of the compressor, Sullair rec-