Atlas Copco LF 2 Instruction Book page 23

Instruction book

Electric cubicle

Air pressure switch (MDR)

On/off switch (S1)

Solenoid valve (Y1)

Unloader (UA) with integrated check valve
Operation
Air pressure switch (MDR) opens and closes its contacts at pre-set pressures. During loaded operation, the
contacts are closed: the motor is running and solenoid valve (Y1) is energized preventing the compressed
air from flowing to unloader (UA).
When the pressure in the air receiver reaches the pre-set maximum pressure, the contacts of pressure switch
(MDR) open. The motor stops and solenoid valve (Y1) is de-energized. Compressed air from the receiver
will flow via the solenoid valve to plunger (8) which causes unloading valve (UV) to open. The air at the
delivery side of the compressor is blown through silencer (US) to atmosphere and check valve (CV) closes
to prevent venting of the receiver.
When the pressure in the air receiver decreases to the pre-set minimum pressure, the contacts of the pressure
switch close. The motor restarts and, after switching over from star to delta, solenoid valve (Y1) is
energized. Control air from the unloader plunger chamber is vented to the atmosphere. Unloading valve
(UV) closes and compressed air is supplied to the receiver again.
LF Trolley up to 15 bar
The regulating system includes:

Pilot valve (RV)

Unloader (UA) with integrated check valve (CV)

Electric cabine (only on electric motor driven Trolley compressors)
Operation
Pilot valve (RV) opens and closes at pre-set pressures. During loaded operation, pilot valve (RV) is closed
preventing the compressed air from flowing to unloader (UA).
When the pressure in the pulsation dampers (PD) reaches the pre-set maximum pressure, pilot valve (RV)
will open. Compressed air from the pulsation dampers will flow to plunger (8) which causes unloading
valve (UV) to open. The air at the delivery side of the compressor is blown through silencer (US) to
atmosphere and check valve (CV) closes to prevent venting of the pulsation dampers. The compressor runs
unloaded.
When the pressure in the pulsation dampers decreases to the pre-set minimum pressure, the pilot valve
closes. Control air from the unloader plunger chamber is vented to the atmosphere. Unloading valve (UV)
closes and compressed air is supplied to the pulsation dampers again.
2920 7090 00
21