Nilfisk SC800 ST User Manual

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Service Manual: SC750, SC800, SC 750 ST, SC800 ST

Form Number 56043150 Page 79

Recovery System

Functional Description

The job of the recovery system is to remove the dirty water from the oor and store it in the recovery tank. The dirty

water is then disposed of. Dirt and water are lied o the oor into the recovery tank by airow created by a vacuum

motor. The wastewater and air enter the vacuum system at the squeegee tool, through notches in the front squeegee

blade. The air and wastewater move through the squeegee vacuum hose at high speed unl it reaches the recovery

tank. The heavier water falls to the boom of the recovery tank. The airow connues through the vacuum fan inlet

port, vacuum motor and exhaust port. A debris tray inside the recovery tanks helps to redirect the water downward and

catches large parcles. No wastewater ever actually moves through the vacuum motor, just the working air. A oang

ball in a cage seals o the vacuum port when the tank is full to protect the vacuum motor from water ingeson. When

the oat ball seats, the amp draw of the motor is reduced and the Main Machine Controller shuts o the vacuum motor.

The squeegee is raised and lowered manually using the squeegee li lever. Springs apply downward pressure on the

squeegee.

Here is how the vacuum motor circuit works. The relay winding is fed baery voltage on terminal 85. The other side of

the relay coil (terminal 86) is connected to a switch inside the controller. To energize the relay, the controller closes the

switch which completes the path to B-. The relay contact terminal 30 is connected to B+. When the relay is energized, the

contacts close connecng 30 to 87 which sends baery voltage to the vacuum motor. Since the other side of the motor is

connected to baery negave, the motor turns on. The Main Machine Controller also monitors the current draw of the

vacuum motor via a “vacuum motor sense” wire. The controller has an internal “voltmeter” that measures the voltage

dierence (drop) between the sense wire and baery negave. A calibrated ground wire of a specic size and length is

used for the motor ground. At a given amperage ow, there is a correlang voltage drop. As the amperage increases the

voltage drop also increases. The controller translates the voltage drop measured into amperage.

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Nilfisk SC800 ST Heavy-Duty Cleaning