FILM-CS-433B 9X6359 - Caterpillar

hydraulic system pressure is controlled three ways. Control is provided by the following valves:
Load sensing signal relief valve
Margin relief valves
Line relief valves
When the travel control spools or implement control spools are shifted, the load sensing signal relief valve limits the pump discharge pressure from the three implement piston pumps. When any implement circuits or any travel circuits are activated, pump discharge pressure is maintained 1900 kPa (275 psi) above the load sensing signal pressure. The pump discharge pressure is limited to 32000 500 kPa (4640 70 psi) for implements and 35000 500 kPa (5080 70 psi) for travel.
If the load sensing signal relief valve fails to limit the pump pressure, the margin relief valves may open. Each implement piston pump has a margin relief valve.The margin relief valves sense the load sensing signal pressure and pump discharge pressure. When the pump discharge pressure reaches 3000 kPa (435 psi) or more above the load sensing signal pressure, the margin relief valve opens. When the margin relief valve opens, some pump flow is sent to the hydraulic tank.Limiting surges in the pump discharge pressure is the primary function of the margin relief valves.
If an external force moves an implement, the circuit's line relief valve limits the circuit pressure to 34000 350 kPa (4930 50 psi).The travel line relief valves are located in the travel counterbalance valves. When the machine is in a travel overspeed condition or when you are stopping the machine, the travel line relief valves limit the pressure in the travel circuit to 38000 700 kPa (5515 100 psi).