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The compressor is provided with a continuous
pneumatic regulating system and a blow-off valve
(BOV), 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
(RVlp RVhp) which, by means of control air to the
unloader assembly (UA), 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 throttle valve is
kept closed via receiver pressure. The compressor
element (CElp CEhp) takes in air and pressure builds
up inside the receiver (AR). The throttle 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.
If the air consumption is equal to or exceeds the
maximum air output, the engine speed is held at
maximum load speed and the throttle valve is fully
open.
If the air consumption is less than the maximum air
output, air receiver pressure increases and the
regulating valve supplies control air to throttle valve
to reduce the air output and holds air receiver pressure
between the normal working pressure and the
corresponding unloading pressure. Unloading
pressure = normal working pressure + 1 bar (14.504
psi).
When the air consumption is resumed, the blow off
valve (BOV) closes and the throttle valve gradually
opens the air intake and the electronic speed regulator
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 throttle valve and the
electronic speed regulator.
Part of the control air is vented into the atmosphere,
and any condensate discharged, through the vent
holes.
ELECTRONIC REGULATING SYSTEM (XRYS)
To be able to control pressure and flow the AirXpert
system watches:
• Ambient air pressure and temperature
• Compressor air inlet pressure
• Vessel pressure and temperature
Depending on the selection Pressure control or Flow
control, the compressor air inlet pressure, the engine
speed and the blow off valve are controlled to keep
the selected setting value (pressure or flow).
The system comprises temperature sensors (TShp
TSlp), pressure sensors (PSlp) and a working pressure
sensor (WPS).
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