789D Off-Highway Truck; Solenoid and Relief Valve (Steering)

Steering solenoid and relief valve (1) Steering solenoid valve (2) Passage (3) Port for right front steering accumulator (4) Orifice (5) Port for the Auxiliary Power Unit (6) Port for right rear steering accumulator (7) Port for inlet oil (8) Passage (9) Port to steering control valve (10) Cavity (11) Port for return oil (12) Cavity (13) Valve (14) Spring (15) Setscrew (16) Backup relief valve (17) Return port to steering hydraulic tank (18) Openings for oil outlet(19) Plunger

(1) Steering solenoid valve (3) Port for right front steering accumulator (5) Port for Auxiliary Power Unit (6) Port for right rear steering accumulator (7) Port for inlet oil (9) Port to steering control valve (11) Port for return oil from the steering metering pump (16) Backup relief valve (17) Return port to steering hydraulic tank(20) Oil sampling valve

The steering solenoid and relief valve is located on the front frame rail under the engine.

The pressure oil from the steering piston pump is routed through port (7) in order to fill cavity (10). Cavity (10) connects the following components: port (7) from the steering piston pump, ports (3) and (6) for the steering accumulators, port (9) for the steering control valve, passage (2) for steering solenoid valve (1) and steering relief valve (16).

Return port (17) drains oil to the steering hydraulic tank. Cavity (12) connects the following components: return port (17), port (11) for return oil from the steering system, passage (2) for steering solenoid valve (1) and steering relief valve (16) .

Steering Solenoid Valve

The steering solenoid valve (1) is used to drain pressure oil from the steering accumulators when the machine is not active.

Pressure of the steering accumulators is in cavity (10). This oil flows through orifice (4) into passage (2). When steering solenoid valve (1) is deactivated, this oil is blocked by plunger (19). When the engine start switch is moved to the OFF position, steering solenoid valve (1) is activated. When steering solenoid valve (1) is activated, plunger (19) moves up. Pressure oil goes through orifice (4) in passage (2), past plunger (19) and out return port (17) to the steering hydraulic tank. Orifice (4) limits the return oil pressure from the steering accumulators to a rate lower than the pressure setting of the filter bypass valve in the steering hydraulic tank. When steering solenoid valve (1) is deactivated, the plunger (19) moves down. Plunger (19) blocks oil in passage (2).

Location of electronic control for the steering accumulators

The steering solenoid valve is activated for 70 seconds. The steering solenoid valve is activated by the electronic control for the steering accumulators when the engine start switch key is moved to the OFF position. The electronic control for the steering accumulators is located under a cover at the rear of the cab. The steering solenoid valve is not activated when the battery disconnect switch or the engine shutdown control is used.

Steering Relief Valve

The steering relief valve protects the steering system if the steering piston pump fails to destroke. The oil in cavity (10) enters passage (8) in steering relief valve (16). If the pressure of the oil is within limits, valve (13) will block the oil. If oil pressure reaches approximately 20700 kPa (3002 psi), valve (13) compresses spring (14). The oil from cavity (10) flows past valve (13) through oil outlets (18). This oil is now open to return port (17) and the oil drains to the steering hydraulic tank.

When the oil in the steering circuit can go through passage (8) and oil outlets (18), the pressure of the oil cannot increase to a pressure higher than the setting of steering relief valve (16). The pressure setting of steering relief valve (16) can be changed by a change in the force of spring (14) that keeps valve (13) closed.

Use the following procedure to change the pressure setting of the steering relief valve:

1. Place the steering relief valve on the test stand.

2. Remove the protective cap.

3. Turn setscrew (15) clockwise in order to increase the pressure setting of steering relief valve (16) .Note: Turn setscrew (15) counterclockwise in order to decrease the pressure setting of steering relief valve (16) .
   The pressure setting of the steering relief valve (16) is 20700 ± 400 kPa (3002 ± 58 psi).

Secondary Steering

The machine does not have a secondary steering pump. If the steering piston pump fails, an Auxiliary Power Unit can be used in order to operate the steering circuit on a disabled machine. The Auxiliary Power Unit connects to port (5) on the steering solenoid and relief valve and to a suction port on the steering hydraulic tank. This arrangement will provide pressure oil in order to charge the steering accumulators. Steering capability is then available to tow the machine.

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789D Off-Highway Truck; Solenoid and Relief Valve (Steering) 2012-12-12T19:15:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown