Gardner Denver L Series Service Manual page 25


When the demand for compressed air rises, the
motor speed is increased in order to keep the
preset setpoint pressure constant.

When the demand for compressed air falls, the
motor speed is reduced in order to keep the
preset setpoint pressure constant.

When the set minimum speed is reached and the
pressure at the system pressure sensor (-28-
(B1)) increases to the set upper maximum value
(network pressure max.), the solenoid valves (-5-
(Y1) and -4- (Y4)) are de-energized.

The pressure control valve (-2.1-) closes.

This happens, because the control chamber of
the actuator (-2.2-) is loaded by the de-
energized solenoid valve (-5 - (Y1)) due to
pressurization.

The screw compressor (-7-) is now running in
the offload mode.

The pressure reservoir (-22-) is now unloaded
to the off-load pressure (residual pressure).

The cooling fan motor (-31-) is switched on or
off in dependence upon the final compression
temperature (only air-cooled units).

The cooling water solenoid valve (-18-(Y6)) is
opened and closed depending on the
compression end temperature (only water-
cooled units).

When the pressure at the system pressure
sensor (-29- (B1)) does not fall to the set lower
switching point within the set motor run-on time
(e.g. 120 seconds), the drive motor (-9-) and the
cooling fan motor (-31-) are shut down and the
system is depressurized to atmospheric
pressure. The cooling water solenoid valve (-18-
(Y6)) de-energizes and closes (only water-
cooled units.

The system is now in the "stand-by" mode and
can restart at any time when the network
pressure falls to the lower switching point (see
section "Starting of the system").

When the pressure at the system pressure
sensor (-28- (B1) falls to the preset lower
switching point before the set motor run-on time
has elapsed, solenoid valves (-5- (Y1) and -4-
(Y4)) are again energized.

The cooling water solenoid valve (-18-(Y6)) is
supplied with power and opens (only water-
cooled units.

The unit now changes over to on-load
operation.
Stopping the system

To de-energize the solenoid valves (-5- (Y1) and -
4- (Y4)) press the OFF push-button on the keypad of
the compressor controller.

The pressure control valve (-2.1-) in the suction
regulator (-2-) closes and the pressure reservoir is
unloaded to atmospheric pressure

The drive motor (-9-) reduces its speed to the set
minimum value and is shut down after 30 seconds.

The cooling fan motor (-31-) is switched on and off
in dependence upon the final compression
temperature for further 20 s. The cooling water
solenoid valve (-318-(Y6)) deenergizes and closes
(only water-cooled units).

The control space of the adjusting cylinder (2.1) is
ventilated by the solenoid valve (-5-(Y1)), the system
pressure causes the choke valve (-2.2-) in the intake
regulator to close.

After 30 seconds, the drive motor (-9-) and the cooling
sir ventilator motor (-31-) are shut down
WARNING
Do not stop the Unit using the Emergency Stop Button unless
there is a danger to the product or of personnel injury.
Using the Emergency Stop Button, disconnect, or breaker to
stop the Unit will not all the Unit to go through an unloading
sequence, and could result in damage to the Motor, Stater, or
other electrical components. Damage caused in this manner
is not covered by the manufacturer's Warranty.
13-25-638 v03 Page 25