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2.5
Oil system
(see Fig. 2.3)
The system comprises:
AR/OS Air receiver/oil separator
RV UA
OC Oil cooler
OF Oil filter
The lower part of the air receiver (AR) serves as oil tank.
Air pressure forces the oil from the air receiver/oil
separator (AR/OS) through the oil cooler (OC) and oil
filter (OF) to the compressor element (CE).
The compressor element has an oil gallery in the bottom
of its casing. The oil for rotor lubrication, cooling and
sealing is injected through holes in the gallery.
Lubrication of the bearings is ensured by oil injected into
the bearing housings.
The injected oil, mixed with the compressed air, leaves
the compressor element and re-enters the air receiver,
where it is separated from the air as described in section
2.4. The oil that collects in the bottom of the oil separator
element is returned to the system through scavenging line
(SL), which is provided with a flow restrictor (FR).
The oil filter by-pass valve opens when the pressure drop
over the filter is above normal because of a clogged filter.
The oil then by-passes the filter without being filtered.
For this reason, the oil filter must be replaced at regular
intervals (see section 4.2).
2.6
Continuous regulating system
(see Fig. 2.3)
The system comprises:
RV Regulating valve
UA Unloader assembly
SR Speed regulator
The compressor is provided with a continuous regulating system.
This system is provided with a blow-down valve which is
integrated in the unloader assembly (UA). The valve is closed
during operation by outlet pressure of the compressor element and
opens by air receiver pressure when the compressor is stopped.
When the air consumption increases, the air receiver pressure will
decrease and vice versa. This receiver pressure variation is sensed
by the regulating valve which, by means of control air to the
unloader, matches the air output to the air consumption. The air
receiver pressure is maintained between the pre-selected working
pressure and the corresponding unloading pressure.
When starting the compressor, the unloader valve (UV) is kept
open by spring force, the engine runs at maximum speed. The
compressor element (CE) takes in air and pressure builds up in the
receiver.
The air output is controlled from maximum output (100%) to no
output (0%) by:
1.
Speed control of the engine between maximum load speed and
unloading speed (the output of a screw compressor is
proportional to the rotating speed).
2.
Air inlet throttling.
If the air consumption is equal to or exceeds the maximum air
output, the engine speed is held at maximum load speed and the
unloading valve is fully open.
If the air consumption is less than the maximum air output, the
regulating valve supplies control air to unloader valve (UV) to
reduce the air output and holds air receiver pressure between the
normal working pressure and the corresponding unloading
pressure of approx. 1.5 bar (21.75 psi) above the normal working
pressure.
When the air consumption is resumed, the unloader valve
gradually opens the air intake and the speed regulator increases the
engine speed.
The construction of the regulating valve is such that any increase
(decrease) of the air receiver pressure above the pre-set valve
opening pressure results in a proportional increase (decrease) of
the control pressure to the unloading valve.
Part of the control air is vented to atmosphere, and any condensate
discharged, through the vent holes (VH).
