Yamaha F150A, Service Manual

Page: 66 / 493

2-21
PTT unit
Trim ram retraction when tilting the outboard motor up
When tilting the outboard motor up, applying the tilt lock lever and pushing the DN button on the PTT
switch applies fluid pressure to the tilt cylinder “1” upper chamber, in the same way as when tilting
the outboard motor down. Because the tilt lock lever is applied, the tilt ram “2” will not operate.
Accordingly, the PTT fluid pressure will increase, releasing PTT fluid from the down-relief valve “3”
to the gear pump side reservoir. The PTT fluid does not flow back inside the gear pump “4”, so the
gear pump “4” attempts to suck PTT fluid up. The passage “a” through which the PTT fluid is sucked
up from the reservoir is small in size, causing oil to be sucked up from the trim cylinder “5” lower
chambers, which have little resistance to suction. This allows the trim rams “6” to be retracted.
Trim ram retraction when there is no load on the tilt ram and trim ram
When the PTT unit has been removed from the outboard motor, operating the PTT motor towards
the DN side will cause the tilt ram “2” to operate in the same way as when tilting the outboard motor
down. If the tilt ram “2” lowers to the limit, PTT fluid pressure increases, releasing PTT fluid from the
down-relief valve “3” to the gear pump side reservoir. The PTT fluid does not flow back inside the
gear pump “4”, so the gear pump “4” attempts to suck PTT fluid up. The passage “a” through which
the PTT fluid is sucked up from the reservoir is small in size, causing oil to be sucked up from the
trim cylinder “5” lower chambers, which have little resistance to suction. This allows the trim rams “6”
to be retracted.
A. Return B. Send
3
4
1
2
5
B
A
6
5
a