Damcos LPU: LPU Power Control System Service Manual
February 2017 SM 8000-100-01 Ed 04
123
Operation LPU-S
Opening
The LPU-S requires only 2 wires for ON/OFF-operation. When the LPU-S is energized, it opens the
valve, runs for 7 sec. extra, and then the motor stops. The valve is kept open by a solenoid valve, pre-
venting the oil from flowing back into the tank.
• If a minor internal leakage over time causes the pressure to fall below the preset pressure switch
level, the pump will restart and run for 7 sec., thus keeping up the pressure. This does not affect
the position of the valve.
• If you want to obtain intermediate positions, the solenoid valve may be connected and con-
trolled separately.
Closing
When the LPU is de-energized, the solenoid valve opens and the oil flow from actuator to tank, which
causes the spring closing actuator to close the valve. This may be used as a fail-safe function.
• If the control system is built up so that the LPU “open” terminal is energized whenever the valve
is to be open. An interruption in the power supply will cause the LPU motor to restart as soon as
the power is reconnected. This will be avoided by defining the system so that only the solenoid
valve is energized. If the valve leaves the required position, the control system must readjust the
valve position by re-connecting, the power supply to the “open” terminal.
Electrical LPU-S
The motor/pump starts directly by means of power on “open” terminal.
The timer stops the motor if the pressure has exceeded the pressure switch set point for 7 sec. This
circuit ensures high safety on the LPU. Furthermore, a thermal safety is built into the motor.
When the valve is open and the pressure drops below set point, there is an automatic restart.
The solenoid valve will keep the unit in open position as long as the unit has power on.
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