COIL-SOLENOID 8I4582 - Caterpillar

Illustration 1 g02077075
Steering and implement pump
(1) Pump control
(3) Load sensing port
(16) Pump inlet port
(17) Pump discharge port
(18) Shaft
(19) Swashplate
(20) Barrel
Illustration 2 g02077078
(1) Pump control
(2) Margin spring
(3) Load sensing port
(4) Adjustment screw for the margin pressure adjustment for the pump
(5) Load sensing spool
(6) Actuator piston
(7) Bias spring
(8) Max limit adjustment (volume)
(9) Pressure passage for the discharge
(10) Pressure passage for the actuator control
(11) Passage for the case drain
(12) Passage for the discharge pressure
(13) Pressure passage for the actuator control
(14) Discharge pressure
(15) Connection to swashplate The pump is a variable displacement piston pump with sensing for load limit control. The flow and pressure are dependent on the system demands that are sensed by the implement and steering valves.The pump draws oil from the hydraulic tank. Oil flows from the hydraulic pump through the margin relief valve to the steering priority valve. Oil is sent to the steering system first. The remaining oil is diverted to the implement system, the implement pilot system, and the differential lock system.When the engine is off, the bias spring (7) holds swashplate (19) at a positive angle. The positive angle allows the pump to produce flow when the engine is started.When the engine is started, shaft (18) starts to rotate. Oil flows into the piston bore from pump inlet port (16). Oil is forced out of pump outlet (17) and into the system as cylinder barrel (20) rotates.When the pump produces flow, the system pressure begins to increase because the oil flow is blocked at the main valves. When the steering and implement pump is in neutral there are no commands. The blocked oil creates pressure, which is felt at the top side of the load sense spool (5) and at the small end side of actuator piston (6). Load sensing spool (5) moves against margin spring (2). When load sensing pressure does not exist at load sensing port (3) the spool will drain oil from the pressure passage for the actuator control (13) to the case drain until there is a pressure balance on load sensing spool (5). The pump will maintain this margin pressure by increasing or decreasing the volume of the pump as needed to create this low standby pressure.When the pressure on the small side actuator piston (6) increases, the force of bias spring (7) is overcome and swashplate (19) is moved to a minimum angle.The pump produces enough flow in order to compensate for normal system leakage when swashplate (19) is moved to a minimum angle. Also, the pump has sufficient pressure in order to provide instantaneous response when an implement or steering is activated.If there is no flow demand from a hydraulic circuit for the implements, no load sensing signal is generated at load sensing port (3).Low pressure standby is higher than margin pressure. The low pressure standby is higher because the priority valve will send a small load sensing signal to load sensing port (3).