SAW SPOOL
SYSTEM
The spool system of the ADI chain saws uses the same spool, spool pin, trigger guard, and handle as the loppers. The only difference is the spool housing. We must use a different spool housing because on a chain saw we are using a hydraulic motor to provide the force as opposed to the cylinder used on a lopper.
Neutral Mode
Trigger Released
The pressurized oil flows through the spool system and is free to flow to both sides of the hydraulic motor and back out of the spool system, again. Because both sides of the motor are exposed to the same pressure, there is no existing pressure drop and as a result the motor won’t turn.
Power Mode
Trigger Engaged
As the spool shifts upward, it directs the pressurized oil to the “IN” side of the motor, causing the motor to turn. The oil then exits the “OUT” port of the motor, returns through the spool system and then out of the tool.
Closed Center
Plug Installed
This time the saw is in neutral mode with the trigger released and the closed center plug installed. The pressurized oil is stopped at the closed center plug and trapped within the spool. Notice on the drawing how the motor “IN” and “OUT” ports are open to the return port of the tool. There is still equal pressure on both sides of the motor. So, despite the high pressure trapped in the tool, the motor does not turn and the seals are not exposed to high pressure.