16
XAHS 146 Dd - XATS 156 Dd - XA(S) 186 Dd - XAVS 166 Dd - XAHS 186 Dd
2.6 OIL SYSTEM
(SEE FIG. 2.4)
The system comprises:
AR/OS Air receiver/oil separator
OC
CE
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
CE
) 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 2.5. 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).
2.7 CONTINUOUS REGULATING SYSTEM
(SEE FIG. 2.4)
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 air
receiver pressure and opens by air receiver pressure via the compressor
element 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 (AR).
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.
3. Blow off valve (BOV).
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 above the normal working pressure.
When the air consumption is resumed, the blow off valve (BOV) closes
and the unloader valve (UV) gradually opens the air intake and the
speed regulator (SR) increases the engine speed.
The construction of the regulating valve (RV) 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 and the speed regulator.
Part of the control air is vented to atmosphere, and any condensate
discharged, through the vent holes (VH).
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