Minimum Pressure Valve; Automatic Blowdown Valve; Pressure Relief Valve; Aftercooler - Sullair ShopTek ST18 Operation & Maintenance Manual

ST18 & ST22 (U.S.A. & Mexico) Operation & Maintenance Manual
ommends installing a wet air receiver after the service
connector.
Additional information
• For the size of the service connector, see Sec-
tion 3.1: Machine specifications on page 17.
2.3.2

Minimum pressure valve

The minimum pressure valve on the top cover of the fluid/
air separator ensures lubricant flow during both normal
operation and start-up by keeping pressure in the fluid/air
separator above 340 kPa (49.3 psi).
When pressure in the fluid/air separator is above 340 kPa
(49.3 psi) and higher than the downstream pipeline pres-
sure, the minimum pressure valve will be opened. Other-
wise, the minimum pressure valve will be closed to
maintain minimum tank pressure.
The minimum pressure valve also functions as a check
(non-return) valve, preventing compressed air down-
stream of the separator from flowing back into the sepa-
rator and air end during compressor blowdown.
2.3.3

Automatic blowdown valve

When the compressor is unloading or stopping, the blow-
down valve in the control line automatically opens to
release pressure. The blowdown valve routes the air to
the air inlet pipe (after the air filter) to prevent a com-
pressed air/fluid mixture from venting into the atmo-
sphere.
2.3.4

Pressure relief valve

To prevent damage to the fluid/air separator and other
compressor components the pressure relief valve located
on the fluid/air separator tank will open when the pres-
sure in the separator tank exceeds the pressure relief
valve setpoint.
Under normal operating conditions, the over pressure
stop switch will shut down the compressor before the
pressure relief valve setpoint is reached (see Section 3.1:
Machine specifications on page 17). However, the pres-
sure relief valve serves as an additional mechanical safe-
guard.
2.3.5

Aftercooler

The aftercooler cools the compressed air to 8 – 12°C
(14 – 22°F) above the ambient temperature. This cooling
causes water vapor to condense, which creates moisture
in the compressed air stream.
88291013-137 R05
Subject to EAR, ECCN EAR99 and related export control restrictions.
2.3.6

Moisture separator

The moisture separator removes the moisture from the
compressed air stream. Moisture collected by the mois-
ture separator can then be safely disposed of according
to local regulations.
The moisture separator ships loose for the cus-
tomer to install if needed for their installation. It is
not installed by the factory.

2.4 Lubrication system

The lubrication system cools the compressor; lubricates
the rotors, bearings, and gears; and seals the air end
against leaks. The primary components of the lubrication
system are the compressor air end, fluid/air separator,
thermal valve, aftercooler, fluid filter, and interconnecting
piping.
2.4.1 General description of the lubrication
system
Fluid is injected into the air end compression chamber,
where it is compressed along with the intake air. The
compressed air/fluid mixture then flows into the fluid/air
separation system, which separates the fluid from the air
and collects the fluid for re-use. Depending on the fluid
temperature, the thermal valve routes none, some, or all
of the fluid to the aftercooler for cooling. Fluid that has
passed through the aftercooler, or that was not routed to
the aftercooler, flows through the fluid filter into the air
end to restart the lubrication cycle.
2.4.2

Lubricating fluid

The lubricating fluid provides three benefits.
• Cooling. The compressor fluid acts as a cool-
ant, absorbing the large amount of heat gener-
ated during compression.
• Lubricating. The compressor fluid forms a
layer between the rotors, preventing the male
and female rotors from making direct contact
and minimizing the surface wear of the rotors.
The compressor fluid also lubricates the bear-
ings and gears.
• Sealing. Compressor fluid with sufficient vis-
cosity can fill the gaps between rotors and
between the rotors and the casing. This
reduces air lost through leakage and increases
the efficiency of the compressor.
2: Description
NOTE
13