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| Illustration 1 | g00754845 |
(1) Load sensing port (2) Left turn port (3) Right turn port (4) Tank port (5) Pump port (6) Gerotor pump (7) Rotary spool (A) Rotary spool section (B) Gerotor pump section | |
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| Illustration 2 | g00754844 |
The metering pump is located on the front of the cab beneath the windshield. (1) Load sensing port (2) Left turn port (3) Right turn port (4) Tank port (5) Pump port | |
The metering pump meters oil from the piston pump (steering) to the steering cylinders. The volume of oil which is metered to the steering cylinders depends on the rotational speed of the steering wheel. The metering pump consists of a rotary spool (7) and a gerotor pump (6) .
The spool within the metering pump contains a integral makeup valve for each steering cylinder. The makeup valves prevent voiding if the steering cylinders are moved by external forces.
The rotary spool, which is infinitely variable, has three positions. The rotary spool is offset when the steering wheel is rotating. The rotary spool is spring centered when the steering wheel is stationary. The oil flow past the rotary spool depends on the rotational speed of the steering wheel. The rotary spool has the following functions.
- The rotary spool directs oil to left turn port (2) or to right turn port (3). This depends on the rotational direction of the steering wheel.
- The rotary spool can direct oil to an output port via the gerotor pump.
- The rotary spool can direct oil to an output port by bypassing the gerotor pump.
- The rotary spool allows a load sensing signal to flow from load sensing port (1) into the load sensing line when the steering wheel is turning. The magnitude of the load sensing pressure depends on the rotational speed of the steering wheel.
- The rotary spool directs oil from port load sensing port (1) to tank port (4) when the steering wheel is stationary.
- The rotary spool blocks oil flow to the steering cylinders when the steering wheel is stationary.
The gerotor pump is coupled to the steering wheel. The volume of oil, which is transfered to the steering cylinders by the gerotor pump, depends on the rotational speed of the steering wheel.
The amount of oil which bypasses the gerotor pump depends on the difference in output between the gerotor pump and the piston pump (steering). As the rotational speed of the steering wheel is increased, the difference in output between the gerotor pump and the piston pump increases. This occurs because an increased load sensing signal causes the piston pump to upstroke. More oil will bypass the gerotor pump and the number of rotations which are required to articulate the machine is reduced.