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| Illustration 1 | g00468195 |
Pressure reducing valve (A) Outlet port (B) Pump pressure port (C) Drain port (1) Adjustment screw (2) Spring (3) Pilot valve (4) Spring (5) Spring (6) Passage (7) Passage (8) Sleeve (9) Orifice | |
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| Illustration 2 | g00468196 |
Location of the pressure reducing valve (10) Pressure reducing valve | |
Pressure reducing valve (10) is attached to the boom and hook control valve which is located below the floorplate in the operator's compartment. Valve (10) reduces the pump pressure to a controllable pressure of 5170 kPa (750 psi) for the pilot control system.
Pump pressure enters port (B) . The oil passes through a cross-drilled hole in sleeve (8) and the pressure is felt at outlet port (A) . This oil also fills spring chamber (5) by passing through orifice (9) . The pressures in port (A) and chamber (5) are equal in this state.
As the pressure from port (B) begins to increase, the pressure that is inside of valve (10) also increases. When the pressure rises above the set point of 5170 kPa (750 psi), pilot valve (3) begins to open. This allows the oil in chamber (5) to exit through pilot valve (3) into port (C) . The oil that is exiting causes a pressure drop in chamber (5) . The oil in chamber (5) cannot be replaced through orifice (9) at a quick enough rate. This pressure drop causes sleeve (8) to move upward. As sleeve (8) moves, port (B) begins to become covered by the sleeve. A large pressure difference between port (A) and chamber (5) causes sleeve (8) to move upward further. This causes port (B) to experience a larger restriction of flow.
Once the pressure in port (A) drops below the set point of 5170 kPa (750 psi), pilot valve (3) closes and the pressure in chamber (5) equalizes. As the pressure increases, the previous process begins again.
Pressure reducing valve (10) also contains a function for pressure relief. If the port (A) receives a sudden increase in pressure, valve (3) is forced open and sleeve (8) moves upward. Sleeve (8) moves upward until port (B) is completely closed. Passage (7) is open to passage (6) in this position. The oil that is inside of valve (10) is allowed to travel through passages (7) and (6) . This oil exits through drain port (C) .