Mercury Mariner 30/40 4-Stroke Outboard Service Manual 1998, Page 294Get this manual
POWER TRIM
Down Mode
When the trim switch is activated in the down position, the electric motor (c) will rotate the pump in the opposite directionWith the oil pump gears rotating backwards, the flow of oil is reversed Oil is drawn through the filter (g)through the down circuit suction port (k) and into the oil pump (DThe pump forces pressurized oil into the down passages, oil will slide the shuttle valve (m) into the up ci rcuit pressure operated valve (n)The shuttle valve will mechanically open the up circuit pressure operated valve and allow oilfrom the up cavity of the trim cylinder (w)to return into the oil pumpThis returning oil, from the up cavity, will supply the oil required for the down circuitThe oil is blocked from returning into the reservoir by the ball (i) inside the up circuit suction portOil, under pressureopens the down ci rcuit pressure operated valve (1) and enters the down passages inside of the manifold (q)The manifold passage connects into the trim cylinder passage leading to the top of the cylinderThe cavity, inside the cylinder, above the shock piston (u) is the down caVityAs the down cavity fills with oilthe piston rod (a) retracts into the cylinder, lowe ring the outboard motorOil from the up cavity exits the cylinder and is drawn back into the pump through the open up circuit pressure operated valve (n)When the piston rod reached full travelthe oil pressure in Side the down circuit will rise until the down pressure regulating valve (e) opens, bypassing oil back into the reservoirWhen the trim button is releasedand the oil pump stops supplying pressure, both of the pressure operated valves (1n) will close and; if open, the down pressure relief valve (e) will close The closed valves will lock the fluid on either side of the shock piston (u)memory piston (I)holding the outboard motor in position