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| Illustration 1 | g00875794 |
Steering metering pump (1) External pump gear. (2) Internal pump gear. (3) Inlet. (4) Outlet. (5) Sleeve. (6) Spool. (7) Body. (8) Drive. (9) Right turn port. (10) Left turn port. (11) Pin. (12) Centering springs. (A) Metering section. (B) Control section. | |
The metering pump has two main sections: pump or metering section (A) and control section (B). The metering section and the control section send pilot oil to the steering control valve. The steering wheel is connected to spool (6) by a shaft assembly and splines.
Oil from the pilot pump flows through inlet (3) into the control section of the metering pump. When the steering wheel is turned the control section sends the oil to the metering section and from the metering section. The control section also sends the oil to the steering control valve and from the steering control valve.
The increased flow causes the steering control valve spool to move farther. As the spool moves farther, more oil can flow from the steering pump to the steering cylinders. This results in a faster turn.
Oil Flow
The control section of the metering pump is a closed center valve. When the steering wheel is in the CENTER (neutral) position, oil flow is blocked by spool (6). Pump oil can not flow through inlet (3) until the steering wheel is turned.
When the steering wheel is turned, spool (6) turns a small amount and springs (12) are compressed. As springs (12) compress, sleeve (5) starts to turn. The spool and the sleeve turn as a unit, but the spool and the sleeve are separated by a few degrees.
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| Illustration 2 | g00875946 |
(1) External pump gear. (2) Internal pump gear. (8) Drive. (11) pin. | |
When the spool and the sleeve are separated by a few degrees, oil passages are opened between the spool and the sleeve. This allows the pump oil from inlet (3) to flow through passages in body (7) to the metering section.
As the steering wheel turns pin (11) turns with the sleeve. The pin causes drive (8) to turn. The drive causes internal pump gear (2) to rotate inner most external pump gear (1). This rotation of the gear senses a metered flow of pilot oil back through body (7) .
The oil then flows to the inlet port (3) or to the outlet port (4). The oil flows to the neutralizer valve from the port. The other port that is not used for pilot oil is used for the return oil from the other neutralizer valve.
When steering wheel rotation is stopped, springs (12) move sleeve (5) in alignment with spool (6) to the NEUTRAL position. This will close passages between the metering section (A) and control section (B).