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AIR FLOW
Air drawn through the air filter (AFc) into the compressor
element (CE) is compressed. At the element outlet,
compressed air and oil pass into the air receiver/oil
separator (AR/OS).
The check valve(CV) prevents blow-back of compressed
air when the compressor is stopped. In the air receiver/oil
separator (AR/OS), most of the oil is removed from the
air/oil mixture: the remaining oil is removed by the
separator element.
The oil collects in the receiver and on the bottom of the
separator element.
The air leaves the receiver via the minimum pressure
Nozzle (MPN) which prevents the receiver pressure from
dropping below the minimum working pressure, even
when the air outlet valves are open. This ensures adequate
oil injection and prevents oil consumption.
A temperature switch (TS) and a working pressure gauge
(PG) are comprised in the system.
A blow-down valve (BDV) is fitted in the unloader
assembly to automatically depressurize the air receiver
(AR) when the compressor is stopped.
OIL SYSTEM
The lower part of the air receiver (AR) serves as the 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 AIR FLOW. 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 Preventive Maintenance Schedule.
For starting applications under 18°F, see Lubrication oils.
CONTINUOUS REGULATING SYSTEM
The compressor is provided with a continuous regulating
system. This system is provided with a blow-down valve
(BDV) 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 unloader valve is
closed.
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
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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).
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