TOHATSU MFS 9.9 Service Manual page 9

PTT Unit
Tilt down/Trim in
Pressing "DOWN" side of PTT switch causes the PTT motor (gear pump) to rotate counterclockwise.
Check valve B opens to cause oil to flow from reservoir toward gear pump and spool valve. This oil flow shifts spool valve
upward to open up-pressure main check valve. Oil in the cylinder lower chamber is returned to gear pump, hydraulic
pressure of oil passage b is increased to open down-pressure main check valve, and the oil flows into cylinder upper
chamber. As a result of the above operations, piston rod is pushed down to tilt down the outboard motor.
The oil in the cylinder lower chamber returns to gear pump through up-pressure main check valve.
Because of difference of capacity difference between cylinder upper chamber and lower chamber, oil of amount exceeding
upper chamber requirement returns to gear pump.
When piston rod is drawn-in completely, all of oil discharged from the pump returns from down relief valve to the reservoir.
8
PTT cylinder
Cylinder upper chamber
Piston
Cylinder lower chamber
Check valve B
Down relief valve
Filter
Tilt rod
Up-pressure main check valve
Spool valve
Down-pressure main check valve
Oil passage b
Gear pump
Up relief valve
Oil reservoir
PTT motor
4st 9.9/15/20 2009