789D Off-Highway Truck: Accumulator Charging Valve

(4) Cap (5) Adjustment screw underneath cap (6) Locknut (7) Drain port to the steering tank (8) Port for signal oil to the pressure compensator valve(9) Port for pressure oil from the steering accumulators

The steering piston pump oil flowing to the steering accumulators is connected to the accumulator charging valve at port (9). While the steering piston pump is charging the steering accumulators, the oil at port (9) will be at low pressure. The position of the spool in the accumulator charging valve will block the oil at port (8). Port (8) is connected to the signal line of the pressure compensator valve. Pressure will increase in this signal line. The pressure compensator valve will keep the steering piston pump at maximum flow.

When the steering accumulators are full, the pressure in port (9) will continue to increase to the cut-out pressure. The cut-out pressure is approximately 18300 kPa (2650 psi). When the cut-out pressure is reached, the spool in the accumulator charging valve will shift. Now, the signal pressure at port (8) drains to the steering tank through port (7). This drains the pressure in the signal line to the pressure compensator valve.

The reduced pressure in the signal line to the pressure compensator valve causes the steering piston pump to destroke to low flow.

Normal leakage in the steering system will cause the pressure in the steering accumulators to gradually decrease to the cut-in pressure of approximately 16470 kPa (2390 psi). (90% of the accumulator charging valve cut-out pressure). At the cut-in pressure, the spool of the accumulator charging valve is shifted by the spring under adjustment screw (5). The signal line at port (8) is now blocked. Oil pressure increases in the signal line to the pressure compensator valve. The pressure compensator valve causes the steering piston pump to stroke up to maximum output.

Steering Accumulator

Location of Accumulators

Two accumulators provide the supply oil during normal operation and for temporary steering if a loss of pump oil flow occurs.

The accumulators are located on the right side of the truck behind the front wheel. A rubber bladder is located inside the accumulator. The rubber bladder is charged with dry nitrogen. The nitrogen charge provides energy for normal steering and for secondary steering capability if steering piston pump flow stops.

The oil pressure in the accumulator maintains the oil in the steering metering pump for quick steering response. The oil pressure prevents hard spots in steering by providing a steady flow of supply oil to the steering metering pump. The steering piston pump only upstrokes when pressure drops below 90 percent of the accumulator charging valve setting.

MARYGAR

789D Off-Highway Truck: Accumulator Charging Valve 2012-12-12T19:13:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown