The air is then compressed in the airend
4
.
The airend is driven by an internal combustion engine
15
.
Cooling oil is injected into the airend. It lubricates moving parts and forms a seal between the ro‐
tors themselves and between them and the airend casing. This direct cooling in the compression
chamber ensures a very low airend discharge temperature.
Cooling oil recovered from the compressed air in the oil separator tank
5
gives up its heat in the oil
cooler
20
. The oil then flows through the oil filter
21
and back to the point of injection. Air pressure
within the machine keeps the oil circulating. A separate pump is not necessary.
A thermostatic valve
19
regulates and optimises the cooling oil temperature. For machines with
Anti-Frost Control, the ambient temperature is considered.
Compressed air, freed of cooling oil in the oil separator tank
5
, flows through the minimum pres‐
sure nozzle
8
into the compressed air distributor
10
. The minimum pressure nozzle ensures that
there is always sufficient internal air pressure to maintain cooling oil circulation.
The cooling fan
28
ensures optimum cooling of all components within the enclosure.
4.4 Operating modes and control mode
4.4.1 Machine 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 de-pressurise the machine.
─ The engine stops.
4.4.2 MODULATING control
The control system regulates the volume of air generated to match the actual demand. The ma‐
chine keeps the working pressure constant by continuously varying the volumetric flow rate within
the machine's regulating range, independent of the air demand.
4
Design and Function
4.4
Operating modes and control mode
No.: 9_9548 22 HCE
Operating Manual Portable Rotary Screw Compressor
MOBILAIR M27 PE
43