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| Illustration 1 | g00453125 |
The steering and brake manifold valve is located on the left side of the machine. The manifold valve is attached to a bracket that is under the front side of the cab.
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| Illustration 2 | g00359962 |
Steering and brake manifold valve (A) Load sensing port. (B) Port from the steering and brake pump. | |
The steering and brake pump supplies hydraulic oil to the steering and brake manifold valve. The steering and brake manifold valve supplies hydraulic oil to the brake system and the steering system. The manifold valve maintains the pressure in the accumulators at a constant range while the engine is running. An internal relief valve in flow control valve (12) limits the signal oil pressure in the steering system. Flow control valve (12) is shown in the following Illustration.
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| Illustration 3 | g01047337 |
The cross section of the steering and brake manifold valve The accumulators are charging. (AA) Supply oil (accumulator pressure) (BB) Signal Oil (CC) Supply oil (tank pressure) (1) Passage (2) Passage (3) Passage (4) Pilot unloading spool (5) Passage (6) Load sensing port to HMU (7) Passage (8) Cavity (9) Spring (10) Chamber (11) Passage (12) Flow control valve with an internal relief valve (13) Passage (14) Poppet (15) Cavity (16) Spring (17) Hydraulic oil tank port (18) Port from the steering and brake pump (19) Cavity (20) Passage (21) Passage (22) Dynamic bleed orifice (23) Ball (24) Passage (25) Piston (26) Spring (27) Accumulator port | |
Illustration 3 shows the steering and brake manifold valve, when the accumulators are charging. Pilot unloading spool (4) is shifted to the left, because the accumulator pressure is insufficient to shift pilot unloading spool (4) to the right. Supply oil (AA) from the steering and brake pump enters through port (18). Port (18) is shown at location (B) in Illustration 2. Port (18) is also shown in Illustration 3 as a hidden line. The supply oil (AA) flows into cavities (19) and (20) .
Repeated applications of either brake pedal will cause the accumulator pressure to decrease below the cut-in pressure. When the accumulator pressure is below cut-in pressure, pilot unloading spool (4) shifts to the left. Spool (4) is pushed to the left by spring (8). In this position, load sensing port (6) is blocked by spool (4). Supply oil (AA) in passage (20) flows through dynamic bleed orifice (22). As a result, the oil pressure builds up to supply pressure (AA) in passage (5), passage (21), and chamber (10). Supply pressure (AA) acts on both the left and right side of flow control valve (12). Therefore, spring (9) pushes flow control valve (12) to the left. Supply oil (AA) that is in passage (20) is blocked to hydraulic oil tank port (17). The blockage increases the supply pressure. The pressure in passage (20) overcomes the force of spring (26) and the oil pressure behind piston (25). Spring (26) compresses and piston (25) and ball (23) shift to the left.
The supply oil (AA) exits to the accumulators through port (27). Supply oil (AA) also flows through passage (2) and (3). The oil pressure in passage (3) acts on the left side of load sensing spool (4). When the accumulators are charging, the pressure is below the cut out pressure. At this time, the oil pressure on the left side of spool (4) does not overcome the forces that act on the right side of spool (4). The force of spring (8) and the oil pressure that is in passage (5) act on the left side of spool (4).
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| Illustration 4 | g01047338 |
Cross section of the steering and brake manifold valve The accumulators charged and steering is in neutral. (AA) Supply oil (accumulator pressure) (BB) Signal Oil (CC) Supply oil (tank pressure) (1) Passage (2) Passage (3) Passage (4) Pilot unloading spool (5) Passage (6) Load sensing port to HMU (7) Passage (8) Cavity (9) Spring (10) Chamber (11) Passage (12) Flow control valve with an internal relief valve (13) Passage (14) Poppet (15) Cavity (16) Spring (17) Hydraulic oil tank port (18) Port from the steering and brake pump (19) Cavity (20) Passage (21) Passage (22) Dynamic bleed orifice (23) Ball (24) Passage (25) Piston (26) Spring (27) Accumulator port | |
When the accumulators are charged, the manifold valve functions as a priority flow control valve, responding to steering and load signal pressure. Illustration 4 shows the cross section of the steering and brake manifold valve, when the accumulators charged and the steering wheel is not turned.
The accumulator pressure is felt on the left side of spool (4). Once the accumulator pressure reaches the cut out pressure, the accumulators are charged. When the accumulators are charged, the accumulator pressure on the left side of spool (4) overcomes the forces that act on the right side of spool (4). The force of spring (8) and the oil pressure in passage (5) act on the right side of spool (4). Now, spool (4) shifts to the right. Spool (4) is not blocking load sensing port (6). This is shown in Illustration 4. Signal oil (BB) from port (6) flows to the HMU. Steering is in NEUTRAL, so the HMU directs the signal oil (BB) to the hydraulic tank.
The pressure decreases in passage (5), passage (21), and chamber (10). The pressure decrease in chamber (10) decreases the pressure that is required in cavity (19) to shift flow control valve (12) to the right. Flow control valve (12) shifts to the right. Hydraulic oil in cavity (19) and passage (20) flows to the hydraulic oil tank port (17). This is shown in Illustration 4.
Signal oil (BB) is constantly replenished from passage (20) through orifice (22). This causes the oil pressure to decrease in passage (20). The pressure in the accumulators is felt in port (27), in passage (24) and behind piston (25). The oil pressure behind piston (25) and the force of spring (26) overcome the pressure in cavity (20). Piston (25) and ball (23) shift to the right.
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| Illustration 5 | g01047339 |
Cross section of the steering and brake manifold valve The accumulators are charged and the steering wheel is turned. (AA) Supply oil (accumulator pressure) (BB) Signal Oil (CC) Supply oil (tank pressure) (DD) Steering pressure (1) Passage (2) Passage (3) Passage (4) Pilot unloading spool (5) Passage (6) Load sensing port to HMU (7) Passage (8) Cavity (9) Spring (10) Chamber (11) Passage (12) Flow control valve with an internal relief valve (13) Passage (14) Poppet (15) Cavity (16) Spring (17) Hydraulic oil tank port (18) Port from the steering and brake pump (19) Cavity (20) Passage (21) Passage (22) Dynamic bleed orifice (23) Ball (24) Passage (25) Piston (26) Spring (27) Accumulator port | |
If the steering wheel is turned, the HMU will block the signal pressure from port (6) to the hydraulic tank. The signal pressure in port (6) increases. This pressure is felt in passage (5), passage (21) and chamber (10). This increases the pressure that is required in cavity (19) to shift flow control valve (12) to the right. As a result, the pressure increases in the hydraulic line that is connected to port (18), which increases the oil flow in the HMU supply line. The HMU supply line is located between the steering and brake pump and the steering and brake manifold valve. Steering pressure (DD) is shown in Illustration 5. The flow control valve meters supply oil to the tank in order to maintain the desired flow rate to the HMU.
The signal oil (BB) will open to the hydraulic oil tank if the relief pressure is exceeded. The signal pressure in chamber (10) is felt in passages (11) and (13). If the signal pressure exceeds the relief pressure, spring (16) will compress and poppet (14) will shift to the left. Signal oil (BB) will flow through cavity (15) and to hydraulic oil tank port (17). Supply oil pressure (AA) is now able to move the flow control valve (12) back to the right. The supply oil in passage (19 ) and passage (20) are directed to the hydraulic tank through passage (17).