1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 307Get this manual
Trim "In"Tilt "DownWhen the hydraulic unit is in the trim intilt down mode, the hydraulic oil is routed from the pump in the following manner: Hydraulic pressure is directed to the reverse lock check valve side of the pump control piston causing the piston to open the trim check valve Fluid then opens the reverse lock check valve against light spring tension and flows through the valve to the top of the tilt cylinder Oil returning from the bottom of the trim and tilt cylinders flows through the trim check valve which the pump control piston is holding open and then back to the input of the pump Because of the area of the tilt rod, less oil is required above the tilt piston than is being supplied to the pump from beneath the pistonSome of the oil from the outlet side of the pump is returned to the reservior through the trim in pump relief valve Q) and in doing so, reduces the volume of oil flowing into the cylindersThe piston movement is then controlled so that the oil returning to the pump equals the combination of the oil flow to the cylinder plus the oil flowing to the reservoir through the trim in pump relief valve Q) the switch is held in the down position after the trim and tilt rods are retracted, the pressure buildup will open the trim in pump relief valve Q) and the fluid will be bypassed back to the reservoirThis valve opens at approximately 2758 kPa (400 psi)