CAP 1H5153 - Caterpillar

Lift Control Valve in FLOAT Position
Illustration 13 g01064953
Illustration 13 shows the lift control valve in the FLOAT position.When the operator moves the lift/lower pilot control lever to the FLOAT position, pilot oil (orange) moves the lift control spool completely to the left. The control spool opens the passage from the check valve to the left side outlet. The control spool opens the passage from the lift cylinder head end to the tank return. The control spool also connects the lift cylinder rod end to the tank return. When the pump and both ends of the lift cylinder are connected to the tank, the lift cylinder cannot be hydraulically raised or lowered.When the machine is moved and the lift/lower control is in the FLOAT position, the implement follows the curvature of the ground.928G IMPLEMENT HYDRAULIC SYSTEM IN THE HOLD POSITION
Illustration 14 g01064954
In the HOLD position, the oil from the steering and pilot pump flows to the steering system supply port and the pressure reducing valve. The pressure reducing valve controls the maximum pressure in the pilot system. Oil flows from the pressure reducing valve, through the check valve to the accumulator, and to the pilot shutoff valve.The accumulator serves as an emergency pilot oil supply when the pump is off.When the pilot shutoff valve is in the OFF position, the pilot oil is blocked. The pilot system will not function. When the pilot shutoff valve is in the ON position, the oil flows through the pilot shutoff valve to the auxiliary, tilt back/dump, and lift/lower pilot control valves. When the pilot control valves are in the HOLD position, the pilot oil is blocked at the pilot control valves. This type of system is called a closed center system.Oil from the main implement pump flows past the test port and the main relief valve to the main control valve.The implement pump oil flows through the center of the auxiliary valve spool, the center of the tilt back/dump valve spool, the center of the lift/lower valve spool and returns to the tank. This type of system is called an open-center system. The open-center system is also an interrupted series circuit, since the return oil from any cylinder is returned to the tank rather than being routed to the next downstream valve.928G IMPLEMENT HYDRAULIC SYSTEM IN THE TILT BACK POSITION
Illustration 15 g01064955
This schematic shows the flow through the hydraulic system with the tilt back/dump control lever in the TILT BACK position.When the operator moves the tilt back/dump control lever to the TILT BACK position, pilot oil flows past the tilt back/dump pilot control valve to the end of the tilt back/dump valve spool in the main implement control valve. Pilot oil moves the tilt back/dump valve spool to the TILT BACK position. Oil from the opposite end of the tilt back/dump valve spool flows past the tilt back/dump pilot control valve to the tank.Movement of the tilt valve spool to the TILT BACK position, blocks the flow of implement pump oil to the tank