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| Illustration 1 | g00617559 |
Hand Metering Unit (1) Control section (2) Outlet to tank (3) Check valve (4) Left turn port (not shown) (5) Inlet from pump (6) Right turn port (not shown) (7) Passage (8) Passage (9) Drive (10) Sleeve (11) Pump section (12) Gerotor (13) Passage (14) Spool (15) Pin (16) Centering Springs | |
The steering control valve is a nonload reaction valve. The steering control valve is a closed centered hand metering unit (HMU).
The hand metering unit is mounted to the operator console. The hand metering unit has two sections:control section (1) and pump section (11). The control section and the pump section work together in order to send oil to the steering cylinder.
The hand metering unit controls the speed and the direction of a turn. As the steering wheel is turned, there is an increase in the flow of oil to the steering cylinder. The increase in flow causes the cylinder to move faster. The increase in cylinder movement causes the machine to turn faster.
In the event of engine or auxiliary pump failure, the pump section (11) will manually pump oil to the steering system. The check valve (3) builds pressure in the pump section in order to allow you to steer the machine.
When the engine is running and the steering wheel is not being turned, the hand metering pump is in the neutral position. The hydraulic oil from the auxiliary pump enters the hand metering unit through the inlet (5) and stops.
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| Illustration 2 | g00618432 |
HMU Component Location (2) Outlet to tank (3) Check valve (4) Left turn port (5) Inlet from pump (6) Right turn port (9) Drive (12) Gerotor | |
When the steering wheel is turned to the left, oil flows to the hand metering unit through the inlet (5) and flows through the internal passages to the check valve (3). The oil causes the check valve to shift left. When the check valve shifts left, oil flows through the spool and the sleeve. Oil flows from the pump to inlet (5) and passage (7). The oil flows through passage (8) from passage (7) into gerotor (12). The oil is directed to the steering cylinder through left turn port (4).
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| Illustration 3 | g00618440 |
Spool and Sleeve (10) Sleeve (14) Spool (17) Slots for springs (18) Grooves for oil flow (19) Holes for pin (20) Small holes for oil flow | |
When the steering wheel starts to turn, the following components will rotate: drive (9), sleeve (10), gerotor (12), pin (15) and spool (14). Sleeve (10) does not start to turn at the same time as spool (14) because the diameter of the pin holes (19) in sleeve (10) are slightly larger than the diameter of pin (15). Spool (14) turns inside sleeve (10) enough to put small holes (20) in sleeve (10) in line with grooves (18) in spool (14). The alignment of holes (20) and grooves (18) provides a path for oil to flow to gerotor (12) and to the steering cylinder.
Centering springs (16) are compressed when spool (14) moves in relation to sleeve (10). When the steering wheel is not longer turning, springs (16) will bring spool (10) and sleeve (14) back to a neutral position. The wheels will stay in the stopped position. You must turn the steering wheel in the opposite direction in order to bring the wheels straight. You must turn the steering wheel in the opposite direction in order to make a right turn.
As the oil goes to the cylinder rod end through left turn port (4) for a left turn, oil from the cylinder head end returns to the HMU through right turn port (6). The oil passes through spool (10) and sleeve (14). The oil then flows back to the hydraulic tank through port (2) .
When the steering wheel is turned for a right turn oil flows into the HMU through inlet (5) and flows through internal passages to check valve (3). The oil causes the check valve to shift left. This forces the oil to flow through the spool and the sleeve. Oil flows from the pump to inlet (5) and through passage (7). From passage (7), the oil flows through passage (8) into gerotor (12). The oil passes through the gerotor to passage (13). The oil is then directed to the steering cylinder through right turn port (6) .
For a left turn, the same components move in the opposite direction. The centering springs cause the spool and the sleeve to return to the neutral position. When the steering effort stops, the wheels will stay in the same position. The steering wheel must be turned in the opposite direction in order to bring the wheels back to the straight ahead position or the opposite position.
As the oil goes to the head end of the cylinder through right turn port (6) for a right turn, oil from the rod end of the cylinder returns to the HMU through left turn port (4). The oil passes through the spool and the sleeve. The oil then flows back to the hydraulic tank through outlet (2) .
If the auxiliary pump fails or the engine cannot be started, the steering system can be operated manually. Turning the steering wheel for a left turn causes drive (9), sleeve (10), gerotor (12), pin (15), and spool (14) to rotate. This causes the gerotor to draw oil from the hydraulic tank through outlet (2). While you operate the system manually, outlet (2) is used to supply oil from the hydraulic tank and return oil to the tank. The oil enters the HMU and the oil causes check valve (3) to shift right. This allows the oil to flow through passage (13) and pump section (11). The gerotor pumps the oil through passage (8) to spool (14) and sleeve (10) .
Sleeve (10) does not start to turn at the same time as spool (14) because the diameter of pin holes (19) in sleeve (10) are slightly larger than the diameter of pin (15). Spool (14) turns inside sleeve (10) enough to put small holes (20) in sleeve (10) in line with grooves (18) in spool (14). The alignment of holes (20) and grooves (18) provides a path for oil to flow from gerotor (12) to the steering cylinder.
Centering springs (16) are compressed when spool (14) moves in relation to sleeve (10). When the steering wheel is no longer turning, springs (16) will bring spool (14) and sleeve (10) back to a neutral position. The wheels will stay in the same position. The steering wheel must be turned in the opposite direction in order to bring the wheels back to the straight ahead position or the opposite position.
As the oil goes to the cylinder rod end through left turn port (4) for a left turn, oil from the cylinder head end returns to the HMU through right turn port (6). The oil passes through the spool and the sleeve. The oil flows back to the hydraulic tank through outlet (2) .
Turning the steering wheel for a right turn causes drive (9), sleeve (10), gerotor (12), pin (15), and spool (14) to rotate. This causes the gerotor to draw oil from the hydraulic tank through port (2). The oil enters the HMU and the oil causes check valve (3) to shift right. This allows the oil to flow through passage (13) to pump section (11). The gerotor pumps the oil through passage (8) to spool (14) and sleeve (10) .
For a left turn, the same components move in the opposite direction. The centering springs cause the spool and the sleeve to return to the neutral position. When the steering effort stops, the wheels will stay in the same position. The steering wheel must be turned in the opposite direction in order to bring the wheels back to the straight ahead position or the opposite position.
As the oil goes to the head end of the cylinder through right turn port (6) for a right turn, oil from the rod end of the cylinder returns to the HMU through left turn port (4). The oil passes through the spool and the sleeve. The oil then flows back to the hydraulic tank through outlet (2).
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| Illustration 4 | g00621076 |
If the unit is taken apart for any reason, the unit must be put back together with the relationship that is shown between pin (15) and rotor (21).