FILM-LOADCHART 4796547 - Caterpillar

Operation of Modulation Relief Valve
The pump oil that flows to pressure differential valve (6) also flows through an orifice to the right end of load piston (5). The right end of the load piston is closed to reservoir (13) by the position of the pressure differential valve. The flow of the oil to the load piston is restricted by the orifice.When the No. 4 clutch is full of oil, the pressure in the speed clutch circuit starts to increase. The increase is felt in the slug chamber at the left end of modulation relief valve (4). When the pressure in the speed clutch circuit is at the initial setting of the modulation relief valve, the modulation relief valve moves to the right. This allows extra oil flow to the lubrication circuit.The pressure that is felt by modulation relief valve (4) is also felt on the right end of load piston (5). The orifice in the supply passage to the load piston causes a short delay in the pressure increase at the right end of the load piston. This pressure increase at the end of the load piston moves the piston to the left. The movement to the left increases the force of the springs. The movement also moves the modulation relief valve to left. This causes a pressure increase in the slug chamber. This will then move the modulation relief valve to the right.The left movement and the right movement of modulation relief valve (4) causes the clutch pressure to gradually increase. The movement to the left of load piston (5) will also cause the clutch pressure to gradually increase. This gradual increase in pressure is known as modulation.The movement of load piston (5) to the left stops when the load piston moves toward the drain passage. At this time, modulation stops. As oil is flowing out of the drain passage, the oil flows through the supply passage to the load piston chamber. This keeps the load piston stationary. The pressure in the system will be limited by the spring force on modulation relief valve (4). At this time, the valve is opened in order to allow the oil flow to the lubrication circuit.Operation of Ratio Valve
Ratio valve (7) controls the maximum pressure to the torque converter. The primary purpose of the ratio valve is the prevention of damaged components of the torque converter.The pressure to the torque converter that is caused by restrictions to flow is felt against the left end of the valve spool. The pressure then pushes the whole diameter of the valve spool.The pressure from the speed clutch circuit is felt in the slug chamber of the valve spool. This pressure pushes only the diameter of the slug.The pressure that is needed on the left end of the valve to move the valve to the right is less than the pressure that is needed in the slug chamber to move the valve to the left. When the inlet pressure to the torque converter reaches