1310 3012 08
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2.6 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 (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 corresponding unloading
pressure of approx. 21.75 psi (1.5 bar) 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).
