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| Illustration 1 | g00836787 |
Accumulator Charging Valve (1) Load sensing orifice (2) Dynamic purge orifice (3) Port to braking system (4) Check valve (5) Test port for braking system (6) Orifice (7) Port to metering pump (8) Port to bank valve (9) Orifice (10) Priority valve (11) Supply port from hydraulic pump (12) Relief valve (13) Test port for hydraulic pump (14) Port to hydraulic tank (15) Port for load sensing (16) Regulator Valve (P1) Passage (P2) Passage (P3) Passage (P4) Passage | |
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| Illustration 2 | g00939868 |
Location of Accumulator Charging Valve | |
The accumulator charging valve is mounted to the frame in the right side of the engine compartment.
The accumulator charging valve provides oil flow on demand and with equal priority to both the steering system and to the braking system. While providing steering and braking oil flow, excess oil flow is also available for the implements.
When the accumulator is fully charged the accumulator charging valve supplies oil flow to the steering system in response to the load sensing signal from the metering unit. If the steering pressure rises above the accumulator pressure then the accumulator is charged up to the higher steering pressure. If the accumulator pressure falls to the preset cut-in level, regulator valve (16) closes the load sensing line. A fixed flow of oil is then supplied in order to charge the accumulator until the preset cut out pressure is reached. Steering capability is available during the charging process.
When the machine is started and the accumulator is discharged, regulator valve (16) is closed due to the action of the valve spring. Priority valve spool (10) is held to the right by the action of the valve spring. Pump flow is directed to passage (P1), passage (P2) and through check valve (4) into the braking lines at port (3) in order to charge the accumulator.
When the accumulator charging valve is in this condition, pressure on either side of the piston in valve (16) is equal. The pressure that is downstream of orifice (6) in passage (P3) is felt on the left side of priority valve spool (10). The pressure that is upstream of orifice (6) is felt on the right side of priority valve spool (10). The flow through orifice (6) creates a pressure drop in passage (P3) so that the pressure on the right side of the priority valve spool is greater than the pressure on the left side of the spool. If the pump output flow is high enough, the pressure differential on each side of the spool will be sufficient to overcome the spool spring and the spool will move to the left. This allows some of the oil to flow to the bank valve. The flow rate to the accumulator is therefore controlled by orifice (6) and the spring in the priority valve spool. As the flow of oil builds up in the accumulator, the pressure of the oil will increase. Pressure will also increase in passage (P2). This pressure is transmitted through passages (P3) and (P4) in order to open regulator valve (16) .
Valve (16) opens when the accumulator pressure reaches the preset cut out pressure. The pressure overcomes the spring in valve (16) and the valve opens. The oil then flows through valve (16) and into the load sensing line at port (15). This creates a load signal to the steering metering unit. When the accumulator is fully charged, check valve (4) is closed in order to prevent oil from flowing back to the pump.
If the steering wheel is stationary, oil in the load sensing line at port (15) is open to the hydraulic tank and the pressure on the left of the spool in priority valve (10) is decreased. The spool moves to the left and some of the oil flow is diverted to the bank valve through port (8). The regulator valve remains open until the reduced pressure in passage (P4) reaches the cut-in pressure. The spring in the regulator valve overcomes the reduced pressure and the valve is closed. The reduced pressure in passage (P4) occurs after several applications of the brake pedal.
The flow of oil through orifice (6) to the braking lines will be reduced if there is a demand from the steering system during accumulator charging. The priority valve spool will adjust in order to maintain the original flow to the braking lines.
When the accumulator is fully charged and the demand from the steering has been met, the pressure increases in the outlet port (7) to the metering pump. The increased pressure is transmitted through orifice (9) and the pressure is felt on the right side of spool (10). Priority valve spool (10) shifts to the left until the forces on both sides are equal. The spool meters the required flow to the steering system and the excess flow is sent to the bank valve through port (8) .
When regulator valve (16) is open, passage (P3) is connected to port (15) and through the load sensing line to the steering metering pump. The steering can now function as a normal dynamic load sensing system. The maximum pressure in passage (P1) is determined by relief valve (12) which must be set higher than regulator valve (16) or by the relief valve in the steering metering pump. The pressure can therefore rise above the maximum setting of valve (16) if the loads on the steering are sufficiently high. The pressure in the accumulator will rise accordingly. The accumulator will therefore operate at a minimum pressure which is set by the cut-in pressure of valve (16). The accumulator will also operate at a maximum pressure which is set by the cut out pressure of valve (16). Alternatively, the accumulator operates at a maximum cut out pressure that is determined by the steering pressure. Both the accumulator and the steering metering pump are capable of working at the same maximum pressure.
Oil flow to the bank valve can be used at a pressure that is independent of the steering or braking pressure but within the limitations of the pump.
Note: Refer to Systems Operation/Testing and Adjusting, "Steering System Pressures-Test and Adjust" for information regarding pressures.