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Wednesday, January 16, 2013

797F Off-Highway Truck Steering System: Relief Valve (Steering) - Test and Adjust - Backup Relief Valve & Steering Control Valve - Adjust





1.-Relief Valve (Steering) - Test and Adjust - Backup Relief Valve

Table 1
Tools Needed    
Tool    Part Number    Part Description    Qty    
A    8T-5320    Hydraulic Test Group    1    
B    9U-6600    Hand Hydraulic Pump    1    
C    3S-6224    Electric Hydraulic Pump    1    

The pressure setting of the backup relief valve is 27580 ± 345 kPa (4000 ± 50 psi) at a flow of 8 ± 2 L/min (2.1 ± 0.5 US gpm). Other components in the steering system will keep the pressure from reaching this value. Use a bench test to achieve an accurate pressure test. The backup relief valve must be removed and tested on a test bench before any adjustments.
Steering solenoid and relief valve
(1) Inlet port
(2) Port to right front steering accumulator
(3) Port to right rear steering accumulator
(4) Port for the Auxiliary Power Unit (APU)
(5) Port to steering control valve
(6) Setscrew
(7) Nut(8) Backup relief valve

A functional test of the relief valve may be performed on the machine.

  1. Remove the hydraulic oil lines from port (2), port (3) and port (5) .

  1. Use Tool (A) to block all three ports.Note: Step 2 prevents the steering accumulators from filling during the test.
    Note: Port (1) does not need to be blocked. The check valve that is mounted in port (1) prevents oil from flowing back into the pump.

  1. Connect Tool (A) or Tool (B) to port (4). Apply pressure.Note: A pressure reading that is between 24000 to 25000 kPa (3480 to 3630 psi) at a flow of 1.6 L/min (0.4 US gpm) is an acceptable reading. The pump supply cannot produce the necessary oil flow that is required to accurately check the backup relief valve.
Use the following procedure to change the pressure setting of backup relief valve (8) :
    Note: Backup relief valve (8) must be adjusted on a test bench.

  1. Loosen nut (6) .

  1. Turn setscrew (7) clockwise in order to increase the pressure setting.

    1. Turn setscrew (7) counterclockwise in order to decrease the pressure setting.Note: One revolution of setscrew (7) will change the pressure setting by 4730 kPa (686 psi).



2.-Steering Control Valve - Adjust

Table 1
Tools Needed    
Tool    Part Number    Part Description    Qty    
A    5P-3032    Hydraulic Test Adapter    1    
4F-7391O-Ring Seal    1    
8S-9191Bolt    4    
1D-4717Nut    4    
2P-1306Tee    1    
1P-5597Fitting    2    
2P-8336Test Valve As    2    
005-8615Pipe Nipple    1    
1P-5570Fitting    1    
4J-0520O-Ring Seal    1    
8C-3206Half Flange    2    
8T-4196Bolt    4    
8T-4121Hard Washer    8    
B    8T-5320    Hydraulic Test Group    1    
C    9U-6600    Hand Hydraulic Pump    1    

The pressure setting of the steering check and relief valves is 28000 ± 1025 kPa (4065 ± 150 psi) at a flow of 10 L/min (2.6 US gpm).
The steering control valve must be tested on a bench test in order to achieve an accurate pressure test of each steering check and relief valve. The bench test is needed to meet the flow requirements.

(1) Steering control valve

(1) Steering control valve
(2) Oil line to the head end of the left steering cylinder(3) Oil line to the rod end of the left steering cylinder

A functional test of the steering check and relief valves may be performed on the machine. Use the following procedure to test the steering check and relief valve in the left turn port of steering control valve (1) .

  1. Remove oil line (2) from the left steering cylinder.
    View of Tool (A) that is installed to the left steering cylinder

  1. Install Tool (A) to the head end port of the left steering cylinder .Note: Tool (A) functions as a tee test adapter when the tool is installed between the oil line and the steering cylinder.

  1. Attach oil line (2) to Tool (A) .

  1. Start the engine.

  1. Steer the truck all the way in the left direction until the steering stop is reached.

  1. Stop the engine.

  1. Connect a pressure gauge from Tool (B) to the test valve that is located on Tool (A) .

  1. Connect Tool (C) to the other test valve that is located on Tool (A) .

  1. Operate Tool (C) and pressurize the steering system.

  1. Record the pressure that opens the steering check and relief valve. If the pressure reading does not fall in the acceptable range, replace the steering check and relief valve.Note: If the steering check and relief valve opens with a pressure reading of 22500 ± 500 kPa (3275 ± 75 psi) at a flow of 1.6 L/min (0.4 US gpm), this is an acceptable reading. This reading is acceptable because the pump supply cannot produce enough oil in order to accurately check the steering check and relief valve.

  1. Remove all tooling from the left steering cylinder.

  1. Reinstall oil line (2) to the left steering cylinder.

  1. Remove oil line (3) from the left steering cylinder.

  1. Install Tool (A) to the rod end port of the left steering cylinder.

  1. Repeat Step 3 through Step 12 for the right steering check and relief valve.Note: For Step 5, steer the truck all the way in the right direction until the steering stop is reached.



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