PIN-YM 3919815 - Caterpillar

Operation
The engine is started normally with the selection lever in the NEUTRAL position. Oil flows to modulating valve (17) through a passage in pressure control valve (12). The oil flows through the modulating valve to pressure differential valve (18). Part of the oil flows through a passage in the pressure differential valve. The remainder of the oil is directed to selector valve (22) .The position of speed selector spool (27) directs the oil into No. 3 clutch. Part of the oil opens the poppet valve in pressure differential valve (18) against the cover of pressure control valve (12). Since valve (18) is against the cover, a passage is open from the chamber to the right end of speed selection spool (27). When speed selection spool (27) is in the NEUTRAL position, the passage is closed to reservoir (24). The pressure in the chamber increases. Valve (18) moves away from the cover of pressure control valve (12) .When the chamber behind the piston in the No. 3 clutch is filled with oil, the pressure in the chamber increases. The higher pressure will move modulating valve (17) against the force of the valve spring. The movement of modulating valve (17) closes the passage from transmission oil filter (20). The pressure increase in the speed clutch stops temporarily.At the same time, the pressure increase in the speed clutch moves pressure differential valve (18) against the force of the valve spring. The movement of pressure differential valve (18) opens orifices in the spool to a passage to selector valve (22). The position of speed selection spool (27) blocks oil flow to a direction clutch. The pressure differential valve also closes a passage from pressure control valve (12) to the reservoir. The movement of the pressure differential valve directs the oil through the center of the pressure differential valve to check valve (13). The check valve closes a passage from pressure control valve (12) to the reservoir. When both of the passages from the pressure control valve are blocked, pressure oil flows through an orifice in check valve (13) to the chamber behind load piston (11) .When the pressure in the chamber behind load piston (11) increases, the load piston moves toward modulating valve (17). The pressure oil behind the load piston and the force of the spring move modulating valve (17). The modulating valve opens the passage from the oil filter to pressure differential valve (18). The position of pressure differential valve (18) directs the oil from pressure control valve (12) to selector valve (22). The pressure in the speed clutch increases.When the pressure in the speed clutch increases, modulating valve (17) closes and the valve blocks the flow of oil to the speed clutch again. Pressure differential valve (18) opens again. The oil flows through the orifice in check valve (13) to the chamber behind load piston (11) again. The pressure behind the load piston and the force of the spring open the modulating valve.The modulating valve opens again and the