The Steering Wheel is Stationary.
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| Illustration 1 | g00628097 |
(1) Steering metering pump (2) Steering cylinders (3) Primary steering pressure switch (4) Secondary steering pump (5) Tank (6) Steering pump (7) Signalling and reducing valve (8) Check valve group (9) Check valve (10) Line from secondary lower valve (11) Shuttle valve (12) Check valve (A) Oil from the hoist pump (B) Return oil (C) Oil in the load sensing system (D) Oil that is blocked | |
The oil from steering pump (6) passes through signalling and reducing valve (7), check valve group (8), and steering metering pump (1). The oil is blocked at the steering metering pump (1) and check valve (9). The steering pump is at standby pressure.
Standby pressure at the check valve group holds the contacts of the control switch for the drive motor of the secondary steering pump open.
A small amount of oil passes through a restrictor in the signalling and reducing valve (7) into the load sensing line. This line is connected to the regulator valve of the steering pump and the steering metering pump. This oil is relieved to tank (5) through a restrictor in the metering pump.
The Steering Wheel is Turning.
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| Illustration 2 | g00628103 |
(1) Steering metering pump (2) Steering cylinders (3) Primary steering pressure switch (4) Secondary steering pump (5) Tank (6) Steering pump (7) Signalling and reducing valve (8) Check valve group (9) Check valve (10) Line from secondary lower valve (11) Shuttle valve (12) Check valve (A) Oil from the hoist pump (B) Return oil (C) Oil in the load sensing system | |
Oil is supplied from steering pump (6) through signalling and reducing valve (7) and check valve group (8) to steering metering pump (1) .
When the steering wheel is turned, the steering metering pump acts as a control valve and a pump which directs oil to steering cylinders (2) .
As the steering wheel is turned, the control section of the steering metering pump is offset. This opens a flow path to the pump section, which rotates with the steering column.
As the pump section rotates, the oil is metered back through the control section to one of the steering cylinder ports. As the steering wheel rotation is increased, some of the oil that is entering the body of the metering pump bypasses the pump section and flows directly from the control section to the steering cylinder port.
Pressure that is developed in the cylinder line is transmitted to the compensator valve of the steering pump through the load sensing line. This signal pressure adjusts the output of the steering pump in order to match the speed and resistance of the turn that is being made.
In the example, oil flows from the steering metering pump to the two following places: The head end of the right steering cylinder and the rod end of the left steering cylinder. This would articulate the machine to the left.
If an outside force prevents the machine from articulating, the steering pump flow will be automatically reduced as maximum system pressure is approached. Examples of outside forces are ruts and obstacles.
When rotation of the steering wheel is stopped, the control section of the steering metering pump is centered by a spring and the majority of the pressure in the load sensing line is relieved to the tank. A small amount of oil is always directed through the pump load sense line. This keeps the steering pump at a slightly higher pressure than the standby pressure of the steering pump. This is referred to as "dynamic bleeding". The steering cylinder ports are closed. This locks oil into the steering cylinder lines in order to hold the machine in the turned position until the steering wheel is turned again.