248B and 268B Skid Steer Loaders Machine Systems Caterpillar

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Personal injury or death can result from escaping fluid under pressure. Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause serious injury and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury. Always use a board or cardboard when checking for a leak.

Before any tests are performed, prepare the machine for troubleshooting. Refer to Testing and Adjusting, "Machine Preparation". Before any tests are performed, visually inspect the machine for oil leaks and damaged parts. Refer to Testing and Adjusting, "Visual Inspection".

Illustration 1	g01115237
(1) Pressure tap for load sensing (2) Margin pressure adjustment (3) High Pressure Cutoff Adjustment (4) Pressure tap for the work tool

Illustration 2	g01424931
(D) Set screw (E) Set screw (1) Load sensing pressure tap (2) Margin pressure adjustment (3) High Pressure Cutoff Adjustment

Margin Pressure for High Flow XPS

The high flow XPS margin pressure is the difference between the system pressure for the work tool and the pressure signal for the load sensing at the pump compensator for the work tool while a work tool is in operation.

1. Raise the cab.

2. Install a 1U-5793 Pressure Differential Gauge between pressure tap (1) on the LSPC variable pump compensator and pressure tap (4) on the work tool control valve.

   1. Connect the hose from the pressure tap (4) of the work tool control valve to the left side of the differential gauge.

   2. Connect the other hose from the pressure compensator (1) of the pump to the right side of the differential gauge.

3. Route the test hoses so that the cab will not rest on the hoses.

4. Install a jumper hose between the A1 and A2 auxiliary on the quick disconnect connectors.

5. Lower the cab. Refer to Operation and Maintenance Manual, "Cab Support Operation" for the correct procedure.

6. Start the machine. Operate each work tool function and the hydrostatic drive system. Operate the work tool and the hydrostatic drive in a forward to rearward positions. Continue until the hydraulic oil is at an operating temperature of 45° ± 5°C (113° ± 9° F).

7. Run the engine at HIGH IDLE.

8. Initiate the standard flow auxiliary circuit A1. Record the pressure on the differential pressure gauge. The pressure should be 2400 ± 200 kPa (348 ± 29 psi).

9. If the margin pressure is not correct, stop the engine. Loosen set screw (E) . Use an allen wrench and adjust the pressure adjustment screw (2) .
   • To increase the margin pressure, turn the pressure adjustment screw clockwise. Pressure difference is approximately 1700 kPa (247 psi) per turn.

   • To decrease the margin pressure, turn the pressure adjustment screw counterclockwise.

   Note: Do not turn the adjustment screw (2) past the compensator body.

10. Recheck the margin pressure by repeating Step 4 through Step 9.

11. Once adjustments are complete, hold the position of the adjustment screw (2) and tighten set screw (E) to 7.5 N·m to 10.8 N·m (5 lb ft to 8 lb ft).

    Note: Do not overtighten the set screw.

12. Reduce the engine speed to LOW IDLE. Stop the engine.

13. Release the auxiliary hydraulic system pressure.

14. Remove the differential pressure gauge.

15. Remove the jumper hose from the A1 and A2 auxiliary quick disconnect connectors.

High Flow XPS Pressure test for the Load Sense Relief Valve

1. Raise the cab.

2. Connect the other end of the 177-7861 Hose As to the pump for the work tool at the test port (1) for the load sensing. Connect the 8T-0860 Pressure Gauge to the other end of the hose assembly.

3. Route the test hoses so that the cab will not rest on the hoses.

4. Lower the cab. Refer to Operation and Maintenance Manual, "Cab Support Operation" for the correct procedure.

5. Start the machine. Operate each work tool function and the hydrostatic drive system. Operate the work tool and the hydrostatic drive system in the forward and rearward positions. Continue until the hydraulic oil is at an operating temperature of 45° ± 5°C (113° ± 9° F).

6. Run the engine at HIGH IDLE. Move the pilot operated control lever for the work tool to the full LOWER position. Hold the control lever for the work tool in the LOWER position until the lift arms reach the fully lowered position. A stall condition will exist.

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NOTICE
Do not stall the hydraulic system for more than 10 seconds. If necessary, release the work tool from the stall condition and wait 30 seconds before you repeat the following step.

7. Record the system pressure for the load sensing during the stall condition. Return the control lever for the work tool to the NEUTRAL position.

8. The pressure of the load sensing should be 20600 ± 700 kPa (2988 ± 102 psi).

9. If the pressure is not within the specification, the relief valve for the load sensing will need to be adjusted.

10. Loosen the locking nut on the relief valve for the load sensing and turn the adjustment screw clockwise in order to increase the setting for the load sensing. To decrease the setting for the load sensing, turn the adjustment screw counterclockwise. Tighten the locking nut to 9 ± 1 N·m (80 ± 9 lb in).

11. Recheck the pressure of the load sensing by repeating 4 through 9.

12. Reduce the engine speed to LOW IDLE. Stop the engine.

13. Release the auxiliary hydraulic system pressure.

14. Remove the pressure gauge.

High Pressure Cutoff for High Flow XPS

The high pressure cutoff test is performed in order to check the pump pressure cutoff in XPS mode for the work tool.

1. Raise the cab.

2. Connect one end of the 177-7861 Hose As to the pressure tap (4) on the work tool control valve. Connect the 8T-0860 Pressure Gauge to the other end of the hose assembly.

3. Route the test hoses so that the cab will not rest on the hoses.

4. Lower the cab.

5. Install the 241-3763 Plug As to the connector of the work tool on the lift arm. This will allow the high flow XPS mode to be enabled.

6. Start the machine. Operate each work tool function and the hydrostatic drive system. Operate the work tool and the hydrostatic drive system in the forward and rearward positions. Continue until the hydraulic oil is at an operating temperature of 45° ± 5°C (113° ± 9° F).

7. Run the engine at HIGH IDLE.

8. Enable the high flow XPS mode by actuating the toggle switch in the cab.

9. Initiate the XPS auxiliary hydraulic function and allow auxiliary function to stall against the blocked coupler.

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NOTICE
Do not stall the hydraulic system for more than 10 seconds. If necessary, release the work tool from the stall condition and wait 30 seconds before you repeat the following step.

10. Record the pressure on the pressure gauge. The pressure should be 28000 ± 1000 kPa (4061 ± 145 psi).

11. If the high pressure cutoff is not correct, stop the engine. Loosen set screw (D) . Use an allen wrench and adjust the margin pressure adjustment screw (3) .
    • To increase the high pressure cutoff, turn the pressure adjustment screw inward. Pressure will increase approximately 4200 kPa (610 psi) per turn.

    • To decrease the high pressure cutoff, turn the pressure adjustment screw outward.

    Note: Do not turn the adjustment screw (2) past the compensator body.

12. Recheck the high pressure cutoff by repeating Step 6 through Step 11.

13. Once adjustments are complete, hold the position of the adjustment screw (2) and tighten set screw (D) to 7.5 N·m to 10.8 N·m (5 lb ft to 8 lb ft).

    Note: Do not overtighten the set screw.

14. Reduce the engine speed to LOW IDLE. Stop the engine.

15. Release the auxiliary hydraulic system pressure.

16. Remove the pressure gauge.

17. Remove the 241-3763 Plug As . Replace the protective cap for the connector of the work tool.