Gardner Denver L Series Service Manual page 24

Stopping the system

Solenoid valve (-5-(Y1)) is de-energized when the
STOP button on the operating panel of the
compressor controller is pressed.

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.
Automatic operation (open-close operation)

When the pressure reaches the unload set point at
the network pressure sensor (-29-(B1)), solenoid
valve (-5-(Y1)) is de-energized.

The upper control space of the adjusting cylinder
(2.2) is ventilated by the solenoid valve (-5-(Y1)), the
pressure spring in the adjusting cylinder causes the
choke valve (-2.1-) in the intake regulator to close.

The oil separator tank is relieved to blow down
pressure (residual pressure) via the blow-off valve (-
4-(Y4)).

The screw compressor is now running in the offload
mode.

The cooling air ventilator (-31-) is switched on or off
in dependence upon the final compression
temperature.

When the pressure at the network pressure sensor
(-29-(B1)) does not fall to the load set point within
the set motor run-on time (e.g. 120 seconds), the
drive motor (-9-) and the cooling air ventilator motor
(-31-) are shut down and the system is
depressurized to atmospheric pressure.

The system is now in the "stand-by" mode and can
restart at any time when the network pressure falls
to the load set point (see section "Starting of the
system").

When the pressure falls to the load set point before
the set motor run-on time has elapsed, solenoid
valve (-5-(Y1)) is energized again.

The unit now changes over to on-load operation.
5.5.1 System control L55RS-75RS
Standstill of the system

If the plant is shut down, the suction
controller (-2-) is closed by a
pressure spring at the adjusting
cylinder (-2.1-).

The solenoid valves (-5- (Y1) and -4- (Y4)) are de-
energized.

The pressure reservoir (-20-) is unloaded
to atmospheric pressure by means of the
solenoid valve (-4- (Y4)) and the actuator
(-2.1-).

The cooling water solenoid valve (-18-
(Y6)) is closed in a de-energized state
(only water-cooled units)
Starting the system

The drive motor (-9-) starts up in the Y-mode.

The cooling water solenoid valve (-34-(Y6)) is
supplied with power and opens (only water-cooled
units).

The intake regulator (-2-) is closed.

The compressor aspires a certain amount of air
through bypass line with check valve Pressure
builds up in the pressure vessel.

Oil is supplied to the screw compressor (-7-)
due to the pressure differential between the
pressure reservoir (-22-) and the place of
injection in the screw compressor (-7-).

After a preset time, solenoid valves (-5- (Y1)
and -4- (Y4)) perform a switching operation,
since they are energized.

The air circulating in the system flows through
solenoid valve -5- (Y1)) into the lower control
chamber of the actuator (-2.2-).

The control chamber of the actuator (-2.2-) is
isolated from the pressure vessel (-22-) by the
solenoid valve (-5- (Y1)) and is bled into the
intake channel.

The choke valve (-2.1-) in the intake regulator
(-2-) opens.

At a reservoir pressure of approx. 65 PSI the
pressure holding and check valve (-28-) opens.

Compressed air is now delivered into the consumer
network.

The system is now in load running mode.
Controlled operation (speed control)
The speed is controlled with the help of a PI controller
implemented in the control software, which regulates the
motor speed in dependence upon the demand for
compressed air. The controller tries to keep the network
pressure constant at the value set for the setpoint
pressure in the control.

When the pressure at the system pressure sensor
(-29-(B1)) reaches the set point value, the network
pressure is kept constant by regulating the motor
speed.
13-25-638 v03 Page 24