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| Illustration 1 | g00315865 |
Steering Metering Pump (A) Control section (B) Metering section (1) Spool (2) Sleeve (3) Tank outlet passage (4) Plug (5) Internal pump gear (6) External pump gear (7) Centering springs (8) Pin (9) Left turn port (10) Right turn port (11) Body (12) Drive | |
The steering metering pump is a component of the servo pilot system which has a closed oil system. The pressure reducing valve maintains a constant oil pressure of 380 ± 35 kPa (55 ± 5 psi) in the servo pilot system.
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| Illustration 2 | g00315866 |
Steering Metering Pump (13) Check valve | |
The steering metering pump is equipped with an oil bypass valve for cold starts. When the system pressure reaches 448 ± 55 kPa (65 ± 8 psi) the check valve (13) opens in order to allow oil to flow to the tank.
The steering metering pump has two main sections:
- Control section (A)
- Pump or metering section (B) .
The two sections work together in order to send pilot oil to the steering control valve.
The control section sends the oil through the metering section and the steering control valve.
The metering section is a small hydraulic pump. The metering section meters the pilot oil that goes to the steering control valve. As the steering wheel is turned faster, there is an increase in the flow of pilot oil to the steering control valve. This increased flow causes the main valve spool to move farther. As the spool moves farther, more oil can flow from the steering pump to the steering cylinders, and a faster turn is made.
Oil Flow
The control section of the steering metering pump is a closed center type valve. The oil from the pressure reducing valve charges the steering metering pump at both ports, left turn (9) and right turn (10) to 380 ± 30 kPa (55 ± 5 psi). The oil is stopped by spool (1) when the steering wheel is in the stationary HOLD position.
The steering wheel is connected to spool (1) by a shaft assembly and splines. When the steering wheel is turned, spool (1) turns a small amount until springs (7) are compressed. Then sleeve (2) turns. The spool and the sleeve turn as a unit when the steering wheel turns.
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| Illustration 3 | g00315869 |
Pump Gears In Metering Section (5) Internal pump gear (6) External pump gear (8) Pin (12) Drive | |
When the steering wheel is turned pin (8) turns with the sleeve. The pin (8) causes drive (12) to turn. The drive causes a rotation of gear (5) inside gear (6) . The rotation of the gear (5) meters pilot oil through body (11) . The oil flows to port (9) or (10) then to the steering control valve.
If the steering wheel rotation is stopped, springs (7) will move sleeve (2) in alignment with spool (1) . This closes passages between the metering section and the control section. The steering metering unit will be in the HOLD position.