4.4 Operating modes and control modes
4.4.1 Operating modes
The machine operates in the following modes:
■ LOAD
─ The inlet valve is open.
─ The engine runs at maximum speed.
─ The airend delivers compressed air.
■ MODULATING
─ With the help of a control valve (the proportional controller) the degree of opening of the inlet
valve is steplessly varied in response to the air demand.
─ The load and fuel consumption of the engine rises and falls with the air demand.
─ The airend delivers compressed air.
■ IDLE
─ The inlet valve is closed.
─ The control valve opens, allowing pressure in the oil separator tank to be applied to the inlet
valve.
─ Compressed air then flows in a closed circuit through the airend, the oil separator tank and
the control valve.
─ The pressure in the oil separator tank remains constant.
─ The engine runs at minimum speed.
■ STANDSTILL (shut down)
─ The inlet valve closes.
─ The venting valve opens to depressurize the machine.
─ The engine stops.
4.4.2 MODULATING control mode
The control system regulates the volume of air generated to match the actual demand. The machine
keeps the working pressure constant by varying the volume of compressed air delivered, thereby
matching the air demand.
With the help of an electrical control valve (the proportional controller), the opening and closing of the
inlet valve is continuously varied in response to the actual air demand. The airend provides com‐
pressed air for connected consumers.
This stepless delivery regulation minimises fuel consumption of the engine. The load and fuel con‐
sumption of the engine rises and falls with the air demand.
4
Design and Function
4.4
Operating modes and control modes
No.: 9_6975 00 E
Service Manual Screw Compressor
M135 SIGMA CONTROL MOBIL
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