Gardner Denver L55 User And Service Manual page 26

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
(- 28 - (B1)) reaches the setpoint value, the network
pressure is kept constant by regulating the motor
speed.
·
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
septoint 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
(- 19 - (Y1) and - 20 - (Y4)) are de-energized.
·
The pressure control valve (- 2.2 -) closes.
·
This happens, because the lower control chamber
of the actuator (- 2.1 -) is unloaded by the de-
energized solenoid valve (-19 - (Y1)) and due to
pressurisation of the upper control chamber in the
actuator (-2.1-) and the compression spring in the
actuator (-2.1-).
·
The screw compressor (- 4 -) is now running in the
offload mode.
·
The pressure reservoir (- 6 -) is now unloaded to the
off-load pressure (residual pressure).
·
The cooling fan motor (- 25 -) is switched on or off in
dependence upon the final compression
temperature (only air-cooled units).
·
The cooling water solenoid valve (-34-(Y6)) is
opened and closed depending on the compression
end temperature (only water-cooled units).
24
·
When the pressure at the system pressure sensor
(- 28 - (B1)) does not fall to the set lower switching
point within the set motor run-on time (e.g. 120
seconds), the drive motor (- 3 -) and the cooling fan
motor (- 25 -) are shut down and the system is
depressurized to atmospheric pressure. The cooling
water solenoid valve (-34-(Y6)) deenergizes 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 (- 19 - (Y1) and - 20 - (Y4)) are
again energized.
·
The cooling water solenoid valve (-34-(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 (- 19 - (Y1)
and - 20 - (Y4) ) press the OFF push-button on the
keypad of the compressor control
·
The pressure control valve (- 2.2 -) in the suction
regulator (- 2 -) closes and the pressure reservoir is
unloaded to atmospheric pressure.
·
The drive motor (- 3 -) reduces its speed to the set
minimum value and is shut down after 30 seconds.
·
The cooling fan motor (- 25 -) is switched on and off
in dependence upon the final compression
temperature for further 20 s. The cooling water
solenoid valve (-34-(Y6)) deenergizes and closes
(only water-cooled units).
·
Then, the cooling fan motor (- 25 -) is stopped.
·
The system is now at standstill.
GD Pilot TS.
August 20, 2018