SUPPORT 2116618 - Caterpillar

Illustration 1 g00277946
Metering pump (HMU) (1) Spool. (2) Sleeve. (3) Outlet to tank. (4) Load sensing line port. (5) Inlet port. (6) Rotor. (7) Rotor ring. (8) Drive shaft. (9) Centering springs. (10) Drive pin. (11) Left turn port. (12) Right turn port. (13) Housing.Control section (A) consists of spool (1), sleeve (2), and housing (13). The sleeve is connected to the spool by drive pin (10). The drive pin is installed through a slot in the spool and a hole in the sleeve. Centering springs (9) are installed through both the spool and the sleeve.Metering section (B) consists of rotor ring (7) and rotor (6). The spool is connected to the rotor by drive shaft (8). The drive shaft has a slot that is engaged with drive pin (10). The drive shaft is splined to the rotor of the metering section.The steering column is connected to the spool by a spline coupling. Pump oil flows into the control section through inlet port (5) .When the steering wheel is not being turned, most of the flow is blocked by the spool and the sleeve. A small amount of flow passes through a restriction to the hydraulic tank. This ensures that a supply of oil that is at the operating temperature is always available at the metering pump.When the steering wheel is turned, spool (1) turns a small amount until springs (9) are compressed. When the drive pin contacts the ends of the slots, the sleeve also turns.While the steering wheel is turning, the spool and the sleeve will turn as one unit. The centering springs are compressed.This initial movement of the spool opens the passages between the control section and the metering section. This allows the oil flow from inlet port (5) to go to the metering section.
Illustration 2 g00277947
Metering Section (6) Rotor. (7) Rotor ring.Steering wheel rotation causes the rotation of rotor (6) inside rotor ring (7). As the rotor turns, a controlled flow of pilot oil flows through the housing. This oil flows to port (12) or to port (11). The oil then flows to the steering control valve.When the steering wheel rotation is stopped, springs (9) move both the spool and the sleeve into alignment. This closes the passages between the metering sections and the control sections.