HEATER GP 4I1275 - Caterpillar

HOLD Position
Illustration 1 g01223344
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 g01223255
Illustration 3 g01223286
When the operator moves the switch (4) to position (3), solenoid (5) is energized. Pilot oil flows through the solenoid to the chamber (6). When the pilot oil overcomes the force of spring (14), spool (13) moves left.Pump supply oil flows from passage (18) around the spool to passage (19). The hydraulic oil from passage (19) flows to the pressure compensator valve (10). 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 (9). The hydraulic oil that flows to chamber (9) and the internal passage is signal oil. The signal oil balances the pressure compensator valve against the hydraulic oil pressure in passage (19). This controls the flow across spool (13) .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 (18) and passage (19) increases. When the hydraulic oil pressure in passage (19) raises above circuit pressure, the hydraulic oil unseats load check valve (8) and load check valve (11). Then, the oil flows to passages (17) and passage (20) .In passage (17), the spool (13) blocks the flow of the oil. In passage (20), the hydraulic oil flows around the spool (13) into passage (21). The hydraulic oil flows through port (7). If the machine contains a multipurpose bucket, the oil flows from port (7) to the rod end of the multipurpose bucket cylinders. This will close the multipurpose bucket. If work tools are installed on the machine, the flow of oil from port (7 ) will pressurize the hydraulic line on the left side of the machine.Hydraulic oil flows from the head end of the multipurpose bucket cylinders or oil flows from the hydraulic line on the right side of the machine through port (12) into passage (16). The hydraulic oil flows around spool (13) into passage (15). The hydraulic oil in passage (15) flows to all control valves as makeup oil. Then, the hydraulic oil flows to the tank.When the operator moves the switch