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| Illustration 1 | g00466647 |
Location of the Metering Pump (Steering) (1) Cover. (2) Metering pump. | |
The metering pump (2) is located behind the cover (1) . The cover is located in front of the cab.
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| Illustration 2 | g00466687 |
Location of the Metering Pump (Steering) (2) Metering pump. | |
The steering wheel is connected to the metering pump by a mechanical linkage.
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| Illustration 3 | g00466688 |
Metering Pump (Steering) (3) Centering springs. (4) Outlet to tank. (5) Internal check valve. (6) Inlet port. (7) Passage. (8) Passage from Gerotor. (9) Drive shaft. (10) Spool. (11) Pin. (12) Passage to the left turn port. (13) Passage to the right turn port. (14) Sleeve. (15) Passage to Gerotor. (16) Gerotor. (A) Control section. (B) Metering section. | |
The steering metering pump is made up of the following two sections:
- Control section (A)
- Metering section (B)
The two sections are connected by hydraulics and by mechanics. The two sections work together in order to send oil to the steering cylinder.
Pump oil goes through inlet (6) into control section (A) . When the steering wheel is turned, control section (A) sends oil to metering section (B) . Metering section (B) produces a specific amount of oil flow. Metered oil from metering section (B) is then directed by control section (A) to either the passage to the left turn port (12) or the passage to the right turn port (13) .
Metering section (B) is a small hydraulic pump. The hydraulic pump produces a metered amount of oil flow. Then, the metered oil is directed by the control section (A) to the steering cylinder.
The direction and the speed are controlled by the metering pump. As the steering wheel is turned faster, there is an increase in the flow of oil from the steering metering pump to the cylinder. The increased flow causes the cylinder to move faster. This turns the machine faster.
When the steering wheel is not being turned, control section (A) is in the NEUTRAL position. The metering pump is a closed center valve. This means that there is no alignment between the passages in the spool and the orifices in the sleeve in the NEUTRAL position. Only a small amount of oil flows through the center position. This keeps the spool slightly open and ready to respond quickly to any steering demands.
When the steering wheel is turned for a right turn, pump oil flows into the metering pump through inlet (6) and passage (7) . From passage (7) , oil flows into Gerotor (16) through passage (15) . While the steering wheel is turned, Gerotor (16) turns. The Gerotor also pumps oil while the steering wheel is turned. The oil flows outward through passage (8) . This oil is directed to the steering cylinder through the right turn port.
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| Illustration 4 | g00466767 |
Spool and Sleeve (10) Spool. (11) Pin. (14) Sleeve. (17) Slots for springs. (18) Grooves for oil flow. (19) Holes for pin. (20) Small holes for oil flow. | |
When the steering wheel started to turn, spool (10) , pin (11) , and drive (9) also started to turn. The sleeve (14) did not start to turn at the same time as the spool. The holes in the sleeve (19) are slightly larger than the pin (11) . The difference allows the spool (10) to turn inside the sleeve (14) . This aligns the small holes in the sleeve (20) with the grooves in the spool (18) . The alignment of the holes and of the grooves provides the path for oil flow to Gerotor (16) and to the steering cylinder.
Centering springs (3) are compressed when the spool moves in relation to the sleeve. When the steering wheel has stopped turning, the springs will return the spool and the sleeve to a Neutral position. When the steering action stops, the wheels will remain in the present position. The steering wheel must be turned in the opposite direction in order to straighten the wheels. The steering wheel must also be turned in the opposite direction in order to make a left turn. For a right turn, oil flows to the cylinder through the passage to the right port (13) . While this happens, return oil from the cylinder comes back into the metering pump through the passage from the left port (12) . This oil is sent to the tank through outlet (4) .
The same components that move for a right turn also move for a left turn. The components which are performing a left turn move in the opposite direction of the components which are performing a right turn. Oil still enters inlet (6) and flows to Gerotor (16) through passage (7) and through passage (15) . The oil exits Gerotor (16) through passage (8) and flows through the sleeve spool combination. The sleeve spool combination is turned in the opposite direction of the right hand turn. This allows a different set of holes to align. This also provides a path for oil to the left turn port (12) . The oil flows from the left turn port to the steering cylinder.
When the machine is off, the internal check valve (5) allows limited manual steering. The metering pump contains crossover relief valves and makeup valves. External forces cause pressure spikes. The valves protect the system from pressure spikes.
The metering pump has a load sensing port. The load sensing port is connected to inlet (6) through an orifice. Oil pressure in inlet (6) is felt in the load sensing line. This signal pressure is communicated to the priority valve. Refer to Systems Operation, "Priority Valve" for an explanation on the operation of the load sensing line and the priority valve.
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| Illustration 5 | g00466768 |
Pump Gears in the Metering Section (9) Drive shaft. (11) Pin. (21) Stator. (22) Rotor. The rotor and the stator are part of the Gerotor (16) . | |
If the steering metering pump is disassembled, assemble the steering metering pump with the proper relationship between rotor (22) and pin (11) . Use Illustration 5 for reference.