1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 306Get this manual
TrimOut" TiltUp"
When operating the hydraulic unit in the trim outtilt up mode, hydraulic oil is routed from the pump in the following manner: Hydraulic pressure is directed to the trim check valve side of the pump control piston causing the piston to open the reverse lock check valve The trim check valve then opens against very ight spring tension and the fluid flows to the base of the trim CD and tilt cylindersOil returning from the top of the tilt cylinder is directed through the reverse lock check valve (which is being held open by the pump control piston) and back to the pump It is important to note that all oil on the return path returns to the pumpBecause the tilt rod displaces fluid on the top of the cylinders, the oil returning to the pump through the reverse lock check is not sufficient to supply the pumpSo, additional oil is drawn from the reservoir as necessaryWhen both the trim and tilt rods are fully extended and the pressure exceeds 5516 kPa (800 psi), the tilt up relief valve and tilt cylinder relief valve will open, bypassing the oil back to the reservoir