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| Illustration 1 | g00514865 |
(1) Outlet port to tank. (2) Inlet port. (3) Outlet port for a left turn. (4) Outlet port for a right turn. | |
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| Illustration 2 | g00514920 |
(5) Load sensing port. | |
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| Illustration 3 | g00514861 |
Metering Pump (1) Outlet to tank. (2) Inlet port. (3) Right turn port. (4) Left turn port. (5) Load sensing line port. (6) Spool. (7) Sleeve. (8) Rotor. (9) Rotor ring. (10) Drive shaft. (11) Housing. (12) Pin. (13) Centering springs. | |
The 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 cylinders.
Pump oil goes through inlet (2) 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 left turn port (4) or right turn port (3).
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 cylinders.
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 cylinders. The increased flow causes the cylinders to move faster and the increased flow causes the machine to turn faster.
Oil Flow
When the steering wheel is in the NO STEER position, the oil is stopped by spool (6). Oil flows to the hydraulic tank through port (1). The oil cannot flow to the metering pump nor to the steering cylinders until the steering wheel is turned.
The steering column is connected to the spool (6) by a shaft and a coupling that is splined.
When the steering wheel is turned, spool (6) turns a small amount until centering springs (13) are compressed. When the drive pinion contacts the ends of the slots, the sleeve (7) also turns.
While the steering wheel is turning, the spool and the sleeve are spread apart by a few degrees. The spool and the sleeve rotate as one unit. The centering springs are compressed.
The initial movement of the spool opens the oil passages between the control section and the metering section. This allows the oil flow from inlet port (2) to go to the metering section.
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| Illustration 4 | g00514892 |
Spool and Sleeve (6) Spool. (12) Pin. (14) Slots for centering springs. (7) Sleeve. (15) Grooves for oil flow. (16) Holes for pin. (17) Small holes for oil flow. | |
When the steering wheel is turned, spool (6), pin (12), and drive shaft (10) start to turn. Sleeve (7) does not turn at the same time as the spool (6), because the diameter of holes (16) in sleeve (7) are slightly larger than the diameter of pin (12). Consequently, spool (6) turns inside sleeve (7) enough to align small holes (17) in sleeve (7) with grooves (15) in spool (6). The alignment of these holes and grooves provides the path for oil flow to the gerotor in the metering section.
The control section (A) sends oil to the steering cylinder. Centering springs (13) are compressed when the spool moves in relation to the sleeve. When the steering wheel is no longer turning, the springs bring the spool and the sleeve back to a center position.
The front end of the machine stays in the turned position when the steering stops. The steering wheel must be turned in the opposite direction in order to straighten the machine.
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| Illustration 5 | g00515875 |
Proper assembly of the gerotor (8) Rotor. (10) Drive shaft. (12) Pin. (18) Stator | |
If the metering pump is disassembled, the gerotor must be assembled in the proper orientation. This orientation is shown in Illustration 5.
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| Illustration 6 | g00515986 |
(19) High capacity cylinder relief valve. (20) Anticavitation valve. | |
113-1726 Metering Pump has a high capacity cylinder relief valve (19) and an anticavitation valve (20). High capacity cylinder relief valve (19) stops a high pressure pulse that is generated at the steering cylinders from jerking the steering wheel. The anticavitation valve (20) prevents the cylinders from voiding. Voiding of the steering cylinders can be caused by very high steering loads.