Construction - Bottarini GDP21 Maintenance And Operating Manual

4. Construction and functional description

4.1 Construction

Compressor and engine
The core of the sound proofed mobile
compressor system is a single-stage, oil-
flooded screw compressor. The
GARDNER DENVER screw profile
represents the state-of-the-art.
The air is delivered pulsation-free.
The drive assembly is a medium-cooled
diesel engine, which drives the screw
rotors of the compressor by a flexible
coupling.
Fairing (Body)
The fairing consists of a monocoque
subframe box to which a canopy which
can be opened for servicing and
maintenance purposes is attached. The
opening of the cover is effectively
supported by pneumatic springs. The
hook inside is for hanging up a load
suspension device. The machine rests on
rubber elements to prevent vibrations and
noise.
For convenient assembly, all individual
parts of the cover are screwed together
with machine screws. For the prevention
of corrosion, the compressor body is fully
galvanised, electrostatically powder
coated and burnt at °C 220. The sound
absorbing mats are inserted and easy to
be cleaned.
Frame and chassis
The complete compressor unit is
mounted on an easy-to-transport single-
axle chassis. The chassis is equipped
with automatic overrun brakes and
parking brakes, as well as a jockey wheel
adjustable in height.
Airflow
Fresh air is sucked in through the
admission opening at the back of the
compressor. The air intake volume is
air for the engine and for the compressor
too, as well as cooling air for the engine
and for the oil cooler of the compressor.
16
4.2 Functional description
(see fig. 8)
Oil circuit
The oil required for sealing and cooling
the rotors as well as for lubricating the
roller bearings is injected into the
compressor (8) from the pressure tank
(15), which is under system pressure.
The difference in pressure between the
pressure tank and the oil injection position
is approx. 1 bar. The oil hereby passes
the oil cooler (14) and the oil filter (11).
The suction controller (9) is fitted with
a non-return function, so that when the
system is switched off, flooding of the air
filter (1) is prevented.
Air circuit
The intake air flows through the air filter
(1) and the suction controller (9) into the
compressor (8). During compression, oil is
injected in order to lubricate, cool and seal
the screw rotors. The compressed air-oil
mixture flows into the pressure tank (15).
Centrifugal preseparation of the oil is
ensured through tangential entry into the
tank.
Any remaining oil is separated from the
air in the fine separator.
The compressed air is fed via the pressure
retention valve (18) to the compressed air
discharge (19). The pressure retention
valve (18) effectively prevents the system
pressure from falling below the minimum
operating pressure required for the system
to work properly. A temperature monitoring
device (12) as well as an operational
pressure manometer
(20) are integral parts of the air circuit.
Regulation
Starting procedure: At start-up, the
connection between the P controller (21)
of the control unit and the adjusting
cylinder (4) for engine speed control is
interrupted by the automatic idling control
solenoid valve 24) for 10 seconds, with
the result that the engine runs up to
maximum speed at minimum system
pressure. The increasing system pressure
immediately closes the intake suction
controller (9). The engine is automatically
adjusted to idling speed after expiry of the
preset time.
Switching from idling to operating speed
takes place by means of actuation of the
load knob load switching valve (22).
The compressor then starts to deliver (8)
and system pressure in the vessel (15)
increases.
When the preset operating pressure is
exceeded the P controller (21) of the control
unit feeds control air to the adjusting
cylinder (4) of the engine speed
adjustment system and the intake suction
controller (9) in order to modify the
comnpressor's intake volume.
This causes a change in engine speed
and in compressor intake volume until the
preset operating pressure is maintained
constant.
The system is kept in equilibrium and
any condensate occurring in the control
line is blown off by means of the nozzle
(5) of the engine management system (4)
and the nozzle (10) of the suction
controller (9).
The speed/intake regulation system
steplessly matches the volumetric flow to
air take-off between 0 and 100 %.
If air tale-off drops to zero, the intake
controller (9) is closed and the diesel
engine (2) is run down to idling speed by
the engine control cylinder (4).
If operating pressure drops below the
preset value, the control air pressure of
the P controller (21) of the control unit; the
intake controller (9) opens and engine
speed in increased by the engine control
cylinder (4).
When turning off the engine the
backlash flap inside the controller will be
closed through the system pressure. The
release valve (23), which closes parallel to
the engine lifting magnet, looses power
and opens. The container pressure drops
down to zero.