Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 206Get this manual
Down Mode When the trim switch is activated in the down position, the electric motor (a) will rotate the pump (n) in the opposite directionWith the pump gears rotating backwards, the flow of oil is reversedOil is drawn through the filterpast the feed check ball (m)into the down circuit oil pick-up and finally into the oil pumpThe pump feeds pressurized oil into the down passages, oil will slide the shuttle valve (p) into the up circuit pressure operated valve (I)The shuttle valve will mechanically open the pressure operated valve and allow oil, from the up cavity of the trim cylinder (f), to return into the oil pumpThis returning oilfrom the up cavity, will supply the oil required for the down circuitThe oil is blocked from returning into the reservoir by the ball (p) inside the up ci rcuit feed valveOil, nder pressure, opens the pressure operated valve (h) and enters the down passages inside of the manifold (f) The manifold passage connects into the trim cyl inder passage leading to the top of the cylinderThe cavity, inside the cylinder, above the shock piston (d) is the down cavityAs the down cavity fills with oil, the trim ram (b) retracts into the cylinder, lowering the outboard motorOil from the up cavity exits the cylinder and is drawn back into the pump through the open pressure operated valve (I) When the trim ram reached full travel, the oil pressure inside the down circuit will rise until the down pressure relief valve (q) opens, bypassing oil back into the reservoi r(t) When th trim button is released, and the oil pump stops supplying pressureboth of the pressure operated valves (hI) will close and; if openthe down pressure regulating valve (q) will closeThe closed valves will lock the flu id on either side of the shock piston (d), holding the outboard motor in position