UPRIGHT A 0358496 - Caterpillar

STANDARD HYDRAULIC SYSTEM IN RAISE POSITION 16. Transmission pump.17. Pilot section relief valve.18. Hydraulic tank.19. Pilot pump section.20. Steering pump section.21. Lift cylinders.22. Lift valve spool.23. Line to steering control valve of steering system.24. Make-up valve for rod end of lift cylinders.25. Load check valve for lift circuit.26. Lift and tilt control valve.27. Implement pump.28. Filter bypass valve.29. Oil filters.FLOAT Operation
When the lift control lever is moved to FLOAT detent position, lower stem (6) moves to FLOAT position. The flow of pilot oil to lift valve spool (22) is the same as in LOWER position. The only difference is the vent passage in lift and pilot valve (5) is opened to hydraulic tank (18) by the movement of lower stem (6). This permits make-up valve (24) to open and lets implement oil go directly to hydraulic tank (18). The head end and rod end of lift cylinders (21) are also open to the hydraulic tank. Outside forces on the bucket will control the movement of the cylinder pistons and rods.The lift control lever must be manually moved out of the FLOAT detent position. There is no kickout for the FLOAT position.LOWER Operation With Engine Off
The bucket can be lowered with the engine off. The pilot oil supply comes from the head end of the lift cylinders. This oil goes through check valve (14) to selector and pressure control valve (10) which decreases the pressure of the oil to approximately 1030 kPa (150 psi). The oil then goes to lift and tilt pilot valve (5). When the lift control lever is moved to LOWER and on to FLOAT detent position, lower stem (6) moves to FLOAT position. Pilot oil goes to lift valve spool (22) and moves it to LOWER position. The head end of lift cylinders (21) is now open to hydraulic tank (18). Make-up valve (24) is vented so it opens and the rod end of lift cylinders (21) is open to hydraulic tank (18) also. The weight of the bucket and lift arms causes the bucket to lower to the ground.
OPTIONAL HYDRAULIC SYSTEM IN CLOSE OR LOWER POSITION 1. Tilt cylinders.2. Relief valve for rod end of tilt cylinders.3. Relief valve for head end of tilt cylinders.4. Main relief valve.5. Lift and tilt pilot valve.6. Lower stem.7. Lift stem.8. Make-up valve for rod end of tilt cylinders.9. Load check valve for tilt circuit.10. Selector and pressure control valve.11. Dump stem.12. Tilt back stem.13. Tilt valve spool.14. Check valve for head end lift cylinder oil.15. Check valve for pilot pressure oil.16. Transmission pump.17. Pilot section relief valve.18. Hydraulic tank.19. Pilot pump section.20. Steering pump section.21. Lift cylinders.22. Lift valve spool. When the engine is off and the lift arms are raised, the bucket can also be dumped.Attachment (Third) Circuit
CLOSE or LOWER Operation
When the engine is running with the control levers in their HOLD positions, pilot pump section (19) takes oil from hydraulic tank (18) and sends it first to pilot section relief valve (17) which controls the