ENGINE AR 1112085 - Caterpillar

HOLD Position
Illustration 1 g03161976
(1) Spool (2) Passage (3) SpringIn the HOLD position, the spring (3) holds spool (1) in the centered position. The spool (1) blocks the flow of pump supply oil in passage (2) .Passage (2) is common to all control valves in the backhoe valve. The spool blocks the flow of pump supply oil until the operator moves the mechanical backhoe control.SWING LEFT Position (Operator Facing Backhoe Control valve)
Illustration 2 g03164476
(1) Spool (2) Port for head end (3) Load check valve (4) Chamber (5) Pressure compensator valve (6) Load check valve (7) Port for rod end (8) Spring (9) Passage (10) Passage (11) Passage (12) Passage (13) Passage (14) Passage (15) PassageWhen swing hydraulic circuit in operation, the swing circuit will have the highest signal oil pressure in the hydraulic system. When the backhoe control lever is moved to the SWING LEFT position, spool (1) moves up spring (8) compressed.When the spool moves up, pump supply oil flows from passage (12) around the spool and into passage (13) .The hydraulic oil in passage (13) flows to pressure compensator valve (5) . In the pressure compensator valve, the hydraulic oil flows into internal passages. The pressure compensator valve moves out. As the pressure compensator valve moves out, the cross drilled passage is opened to an internal passage that is in the valve. Some of the hydraulic oil flows inside the pressure compensator valve to chamber (4) . The hydraulic oil that flows to chamber (4) is signal oil. The signal oil balances the pressure compensator valve against the hydraulic oil pressure in passage (13) . This controls the flow across spool (1) .The signal oil in the internal passage flows to the pressure compensator valve (5) in each control valve. The signal oil also flows to the pressure and flow compensator 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 (12) and passage (13) increases. When the hydraulic oil pressure in passage (13) rises above circuit pressure, the hydraulic oil unseats the load check valve (3) and the load check valve (6) . The hydraulic oil flows to passage (11) and passage (14) .In passage (14) , spool (1) blocks the flow of oil. In passage (11) , the oil flows around the spool (1) to passage (10) . Then, the oil flows through port (7) to the rod end of the LH swing cylinder.There are two cylinder crossover lines. One line connects the rod end of left swing cylinder to the head end of the