TOHATSU MFS 9.9 Service Manual page 8

Tilt up Operation
Pressing "UP" side of PTT switch causes the PTT motor (gear of gear pump) to rotate clockwise.
Check valve A opens to cause oil to flow from reservoir toward gear pump and spool valve. This oil flow shifts spool valve
downward to open down-pressure main check valve. Oil in the cylinder upper chamber is returned to gear pump, hydraulic
pressure of oil passage a is increased to open up-pressure main check valve, and the oil flows into cylinder lower chamber.
As a result of the above operations, piston rod is pushed up to tilt up the outboard motor. The oil in the cylinder upper
chamber returns to gear pump through down pressure main check valve.
Because of difference of capacity difference between cylinder upper chamber and lower chamber (piston rod at upper
chamber side), oil flows into the pump through check valve A to compensate for the lack of the oil. When the motor stops,
down/up pressure main check valve closes, and spool valve moves to the center. As a result, piston rod is held at a position
at the time.
When tilt rod fully extends, up relief valve opens to prevent increase of hydraulic pressure of cylinder lower chamber by
relieving the pressure to protect PTT unit.
4st 9.9/15/20 2009
Cylinder upper chamber
Piston
Cylinder lower chamber
Check valve
A
Down relief valve
Tilt rod
Up-pressure main check valve
Spool valve
Down-pressure main check valve
Gear pump
Oil passage
Up relief valve
Oil reservoir
PTT motor
a
7