SUPPORT-TRUNNION 1189404 - Caterpillar

The pilot hydraulic system is used to move the spools in the control valve (work tool) (6). The pilot hydraulic system is also used to control the operation of the hydrostatic system. The pilot system uses lower pressure oil to control higher pressure oil. In order for the pilot system to function, the interlocks must be disengaged. The interlock system consists of the following components: the solenoid valve ( hydrostatic) (2), the solenoid valve ( work tool) (3) and the solenoid valve ( parking brake) (11). In order for the interlock system to be disengaged, the following conditions must be met:
The seat must be occupied.
The armrest must be in the DOWN position.
The parking brake must be disengaged.The charge relief valve (16) regulates the pressure of the charge system. The charge system pressure is 3300 kPa (480 psi) at high idle.When the interlock system is disengaged, oil flows from the hydraulic tank (19) to the front section of the gear pump (18) and then oil flows to the gear motor (fan drive) (14). After the gear motor, oil flows through the oil filter (13). Then, the oil flows to the piston pump ( hydrostatic) (17). Some of the oil tries to flow to the pilot operated hydraulic control ( work tool) (4), but the oil is blocked by the solenoid valve ( work tool).The oil continues to flow to the piston pump. At the piston pump, the oil is regulated by the speed sensing valve (15). The oil that flows to the pilot operated hydraulic control ( hydrostatic) (1) is regulated at a pressure of 2500 kPa (365 psi).The rest of the oil is makeup oil for the hydrostatic system. Any leakage in the hystat system is replaced by this oil. Pilot Operated Hydraulic Control ( Hydrostatic)
Illustration 2 g00799349
(1) Pilot operated hydraulic control ( hydrostatic) (2) Solenoid valve ( hydrostatic) (10) Accumulator (11) Solenoid valve ( parking brake) (15) Speed sensing valve (16) Charge relief valve (17) Piston pump ( hydrostatic) (18) Gear pump (19) Hydraulic tank (20) Resolver network (21) Left piston motor ( hydrostatic) (22) Right piston motor ( hydrostatic) (23) Actuator piston (24) Actuator piston (X3) Pilot pressure ports (X4) Pilot pressure portsOil that comes from the speed sensing valve (15) flows to the pilot operated hydraulic control ( hydrostatic) (1). When the interlock system is disengaged, signal oil will not flow through the pilot operated hydraulic control until the hydraulic control is moved out of the HOLD position. The hydraulic control will return to the HOLD position when the hydraulic control is released from any of the positions. Table 1 shows the direction of machine travel when the signal ports are pressurized by the pilot operated hydraulic control ( hydrostatic).
Table 1
Ports that are Pressurized     Direction of Machine Travel    
Port (X3) on Rotating group 1 and Port (X3) on Rotating group 2     REVERSE    
Port (X3) on Rotating group 1 and Port