BRACKET AS 3746280 - Caterpillar

Oil from the pilot pump section of pump group (16) goes to pilot control valve (15). There, the pressure of the oil is reduced to pilot system pressure. A secondary source of pilot oil is also sent to pilot control valve (15) for lowering the bucket when the engine is stopped. The pressure of this oil is reduced below pilot system pressure. A selector valve sends the pilot supply oil with the higher pressure to the on/off solenoid valve. When the on/off solenoid valve is open, pilot oil is sent to the proportional control valves. When the engine is running, the on/off solenoid valve will remain open. When the engine is off and the engine start key is in the ON position, the on/off solenoid valve will open with any movement of the control levers. (The implement lockout switch must be in the UNLOCKED position.)The pilot oil does not go through the pilot control valve when the control levers are in the HOLD position. When a control lever is moved, a proportional solenoid valve in pilot control valve (15) opens in order to allow pilot oil to flow to main control valve (7). Then, the pilot oil moves a valve spool in main control valve (7). This allows oil from implement section (20) to flow to the lift cylinders or to the tilt cylinders.If the machine is equipped with an auxiliary pilot valve, pilot oil will be supplied to the auxiliary valve from the pilot pump section of pump group (16). The auxiliary pilot valve operates in the same manner as the pilot control valve.The pressure reducing valves (14) in the pilot control valve maintain the pilot system pressure. The flow of oil which is not needed for the operation of the pilot control valve or for the operation of the brakes is routed back to hydraulic tank (24) .Implement pump (20) provides the oil that operates the lift cylinders and the tilt cylinders. The oil flows to main control valve (7). This control valve is an open centered valve with two spools. One spool is for the lift functions and the other spool is for the tilt functions.The oil from the pilot system causes the valve spools to move. When the valve spools are in the HOLD position, the oil flows through main control valve (7) and back to hydraulic tank (24) .Main relief valve (12) is for the flow of oil from implement section (20). The main relief valve opens when the oil pressure from the implement section to the implement cylinders rises to approximately 20700 kPa (3000 psi). (This does not include the oil to the rod ends of the tilt cylinders.)The rod end line relief valve for the tilt cylinder opens when the cylinder oil pressure rises to the following level:
14500 kPa (2100 psi) for a standard control valve
12400 kPa (1800 psi) for an auxiliary control valveThe head end line relief valve for the tilt cylinder opens when the cylinder oil pressure rises to