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| Illustration 1 | g01389904 |
(1) Relief valve (2) Priority valve (3) Signal port (4) Steering port (5) Pump port (6) Tank port (7) Chamber (8) Spool (9) Spring (10) Chamber | |
The priority valve is bolted to the lift control valve on the loader control bank valve. Relief valve (1) is installed in the priority valve on all of the machines except the 422E. The relief valve prevents the oil pressure in the load signal circuit for the loader function from becoming too high. Load signal oil that has flowed through the relief valve flows out of the inlet manifold through port (6) to the tank. The port is labeled "T".
Oil flows from the hydraulic pump through port (5). The port is labeled "P". The supply of oil to the metering pump flows out of port (4). The port is labeled "D". Load signal oil flows from port (3) to the bank valve for the backhoe. The port is labeled "LS". Oil returns from the circuits in the loader control bank valve flow to the tank through port (6). The port is labeled "T".
Oil enters the priority valve through port (5). Spring (9) holds spool (8) to the right preventing the oil from flowing to the control valves in the loader control bank valve. The oil flows around the spool into passage (7). The oil flows through port (4) to the steering circuit. Some of the oil flows into passages that are cut in the spool. Oil is inside the spool, and on the ends of the spool in chamber (7) and chamber (10) .
As oil flows into the steering circuit, the oil pressure in the priority valve raises. When the oil pressure overcomes the force of spring (9), spool (8) moves to the left. The oil flows around the spool to passage (10). Then, the oil flows to the control valves in the loader control bank valve.
When the steering wheel is turned, the metering pump requires more oil. The metering pump causes a pressure drop in the passage (7) to the metering pump. This pressure drop is sensed in chamber (10). Passages that are cut in the spool allow the oil to flow from chamber (10) to passage (7) reducing the oil pressure in chamber (10). Spring (9) will cause priority spool (8) to move to the right. When the priority spool moves to the right, the spool reduces the flow of oil to the loader control bank valve and directs more pump supply oil to the metering pump.
On certain machines, The inlet manifold of the loader contains relief valve (1) for the load signal oil. Internal passages that are in the inlet manifold of the loader connect the load signal oil from the control valves to the load signal oil from the steering circuit. This allows the circuit with the highest pressure to control the flow of oil from the pump. If the oil pressure in the circuit for the signal oil gets too high, relief valve (1) opens. The oil flows through the relief valve through port "T" to the tank.