SENSOR GP-ENGINE 2964802 - Caterpillar

Accumulators
Accumulators (2) provide the cushion (shock absorber) for the cushion-hitch. Each accumulator has a sealed piston that moves up and down inside its bore. The chamber above the piston has a charge of dry nitrogen gas. The charge of dry nitrogen gas is put into the accumulator through valve (1). Oil from the pump and the leveling valve comes through outlet (3) into the chamber below the piston. The oil pushes the piston up and causes compression of the dry nitrogen gas.The accumulators keep a constant supply of oil available to the load cylinder. They also prevent (absorb) sudden shocks caused by the load cylinder. This gives the tractor a smoother ride. The front accumulator has the higher pressure.
RIGHT SIDE OF HITCH
1. Nitrogen charging valves. 2. Accumulators. 3. Outlet to leveling valve.Cushion-Hitch Hydraulic System
Lockdown Operation
When the engine is started, oil from hydraulic tank (14) goes to hydraulic pump (5) and servo valve (10). When the output of the pump is lower than the setting of the servo valve, the hydraulic pump is at maximum output (displacement). The setting of servo valve (10) is approximately 16 000 kPa (2300 psi).The oil then goes to accumulator bleed valve (9). Check valve (4) and spool (8) move to the left. The oil goes through check valve (4) to selector valve (3).When the control lever is in LOCKDOWN position, the pump oil to selector valve (3) goes around valve spool (1) to piston (2). The piston moves to the left against the spring force. Whenever the pressure of the oil on piston (2) is stopped, the spring force pushes the piston back to the right. If valve spool (1) is in CUSHION-HITCH position, the valve spool will automatically move to LOCKDOWN position.As pump oil goes to selector valve (3), pump oil also goes to leveling valve (6) and divides. When the engine is first started, leaf spring (12) has leveling stem (11) in the RAISE (up) position. The oil goes around leveling stem (11) and directional spool (7) to the rod end of load cylinder (15). The weight of the scraper retracts the rod as far as it will go (LOCKDOWN position). The head end of load cylinder (15) is open to hydraulic tank (14) because of the position of the directional spool.The oil from leveling stem (11) also goes to accumulators (13). The oil charges the accumulator to approximately 16 000 kPa (2300 psi). At this time, servo valve (10) causes the swashplate of hydraulic pump (5) to move to its minimum angle. The pump is now at minimum displacement and pressure in the system is at the maximum.
CUSHION-HITCH HYDRAULIC SYSTEM (Engine Running, LOCKDOWN Position) 1. Valve spool.2. Piston.3. Selector valve.4. Check valve.5. Hydraulic pump.6. Leveling valve.7. Directional spool.8. Spool.9. Accumulator