Mercury 225 EFI, Service Manual

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POWER TRIM - DESIGN II
Page 5B-16 90-884294 OCTOBER 2001
Down Circuit
When you depress the down button, the power trim pump (1) is activated in the opposite
direction. As the oil pump gears begin to rotate, oil is drawn through the down circuit suc-
tion check valve (2) and into the pump, suppling flow for the down circuit. Down circuit oil
pressure is lowered by the down pressure regulating valve (3) (640 psi to 1050 psi) allow-
ing excess oil to return into the reservoir (4). Oil is blocked from returning into the reservoir
by the closed up circuit suction check valve (5). Oil under pressure then moves the shuttle
spool (6) to the right, mechanically opening the “up” pressure operated valve (7), allowing
oil from the bottom of the trim (8) and tilt cylinders (9) to supply oil to the trim pump for the
down circuit. At this same time, oil under pressure opens the down circuit pressure oper-
ated valve (10) allowing oil to exit through the down pressure port. The oil then continues
through the down pressure passage, through the pivot pin (11), and into the interconnect-
ing passage of the tilt cylinder leading to the cavity above the shock piston (12), and
pushes the piston and ram assembly in (down). As the outboard engine contacts the ex-
tended trim rams (13), the weight of the motor, propeller thrust and pump down pressure
will force the trim rams to retract.