ENGINE AR 7C7475 - Caterpillar

HOLD Position
Illustration 1 g01224712
In the HOLD position, the spring (3) holds spool (2) in the centered position. No pilot oil enters the control valve through the port (4) and chamber (5). Any pilot oil in the pilot lines drains through the pilot valve to the tank. The spool (2) blocks the flow of pump supply oil in passage (1) .Passage (1) is common to all control valves in the bank valve. The passage has no outlet. The spool blocks the flow of pump supply oil until the operator moves the pilot valve.Flow to Port A
Illustration 2 g01224671
Right joystick for the backhoe
Illustration 3 g01224826
When the operator moves the switch (4) to position (3), the electronic signal goes to the machine ECM. The machine ECM energizes solenoid (21). Pilot oil flows through the solenoid to the passage (20). When the pilot oil overcomes the force of spring (12), spool (11) moves to the right.Pump supply oil flows from passage (16) through the metering slots in the spool to passage (17). The hydraulic oil from passage (17) flows to the pressure compensator valve (9). In the pressure compensator valve, the hydraulic oil flows into internal passages. The pressure compensator valve moves up. As the pressure compensator valve moves up, a cross-drilled passage is opened to an internal passage in the valve. Some of the hydraulic oil flows around the pressure compensator valve to chamber (6) and chamber (7). The hydraulic oil that flows to chamber (7) and the internal passage is signal oil. The signal oil balances the pressure compensator valve against the hydraulic oil pressure in passage (17). This controls the flow across spool (11) .The signal oil in the internal passage flows to the pressure compensator valve in each control valve. The signal oil also flows to the pump control valve on the hydraulic pump. The signal oil helps to control the output of the hydraulic pump. The hydraulic pump upstrokes and the hydraulic oil pressure in passage (16) and passage (17) increases. More oil flows to chamber (6). When the hydraulic oil pressure in passage (6) raises above circuit pressure, the hydraulic oil unseats load check valve (8). Then, the oil flows to passages (15) and passage (18) .In passage (15), the spool (11) blocks the flow of the oil. In passage (18), the hydraulic oil flows around the spool (11) into passage (19).
Illustration 4 g01224833
When the oil pressure overcomes the force of spring (22) and spring (23), the lower section (24) of the poppet moves upward. Oil flows through the lower section (24) of the poppet into chamber (26). The oil flows through section (27) of the poppet. The oil then flows through the port (5). As the flow of oil increases, the ball (25) moves up. Spring (23) is compressed more. Oil flows around the ball (25) into chamber (26). This oil helps balance the pressure in chamber (26) and chamber (19) .The oil flows from port (5) to the rod end of