PANEL A. 1H4397 - Caterpillar

Illustration 1 g00526844
(1) Pilot flow control valve (2) Pilot pressure relief valve (3) Low flow pressure relief valvesThe pilot pressure relief valve that is installed in the pilot manifold is a direct controlled pressure limiting valve. The pilot pressure relief valve restricts the pilot pressure to approximately 3000 kPa (435 psi).The pilot pressure oil at the inlet port enters the relief valve through an orifice to the bottom of the piston. When the pressure exceeds the relief valve pressure setting, the piston is shifted upward in order to open a passage to the hydraulic tank.
Illustration 2 g00526839
Pilot Flow Control Valve
The supply oil from the wheel brake valve enters the pilot manifold through the pilot flow control valve. When the oil flow that is acting on the pilot flow control piston is less than 15 L/min (4 US gpm), the piston blocks the flow of oil to the attachment. When the oil flow increases to at least 15 L/min (4 US gpm), pressure develops at the piston in order to shift the piston upward. Oil flow is now supplied to the attachment circuit while the priority is maintained to the pilot circuit.Low Flow Pressure Relief Valve
The low flow pressure relief valve is a pilot operated valve that is installed in the pilot manifold.The pressure oil at port "P" enters the low flow pressure relief valve from the drain passage in the pilot flow control valve. When the low flow attachment pressure increases, the valve cone is forced upward against the force of the spring. When the valve cone opens oil is sent to the hydraulic tank. As a result of the pressure drop inside the valve, the drain piston moves upward and the pressure is released.