Mechanical Features; Engine; Compressor; Compressor Elements - Atlas Copco PTS 1600 Cud S3A/T3 APP Instruction Manual

3.3

Mechanical features

3.3.1 Engine

The compressor is driven by a liquid-cooled diesel
engine, manufactured by Cummins. This engine has
the following characteristics: direct fuel injection,
electronic unit injection that is mechanically actuated,
turbocharged, and air-to-air aftercooled.
For general description, see Engine Operation
Manual (EOM).

3.3.2 Compressor

The compressor has one low-pressure and one
medium-pressure compressor element, individually
bolted to the housing of a common step up gear. The
step up gear is bolted directly to the engine flywheel
housing. The power from the engine is transmitted to
the step up gear shaft through a flexible coupling.

3.3.3 Compressor elements

Each compressor element houses two screw-type
rotors, mounted on ball and roller bearings. The male
rotor, driven by the step up gear, and the female rotor
are synchronized through timing gears, which
maintain the slight clearance between the rotors.
The male rotors have four lobes and the female rotors
six flutes. Thus, the male rotors revolve at 1 1/2 times
the speed of the female rotors. The absence of contact
between the rotors and between the rotor crests and
the compressor casings eliminates wear and power
loss. The elements deliver pulsation-free air.
Air and oil sealing rings are fitted on the rotor shafts.
The air seals are located next to the compression
space, the oil seals next to the rotor bearings. The leak
air from the air seals is evacuated to the atmosphere
through vent-holes. Any oil that might gather
between the oil and air seals is prevented from
entering the compression space, as it is drained
through the same vent holes.

3.3.4 Cooling and lubrication

The radiator, intercoolers, aftercooler and oil cooler
are installed side by side in the front of the unit. These
coolers are air-cooled by an axial fan, which is belt-
driven from the compressor main-shaft.
The unit is provided with a second aftercooler, with
water separator, CAC (= charge air cooler) / fuel
cooler placed in the back of the unit. The cooling air
is generated by an axial fan, which is belt-driven from
the engine fan shaft.
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Water condensate from the water separator is drained
through a nipple in the bottom of the frame in the back
of the unit.
Oil is used for jacket-cooling of the compressor
elements, as well as for lubricating the rotor bearings,
timing and drive gears. The system includes an oil
pump and an oil filter.
3.3.5 Speed regulation and unloading
system
The regulation of the unit is governed by the Engine
Controle Module (ECM) and the Compressor Control
Module (CCM), which will vary engine speed and
operate the compressor throttle valve and unloading
valve through a 3-way loading valve.

3.3.6 Safety devices

Two relief valves and a MP safety valve protect the
LP and MP sides of the compressor respectively.
A check valve prevents blow-back of compressed air
when the compressor is unloaded or stopped.
Pressure and thermal shutdown switches protect the
compressor against abnormal operating conditions.