374D Excavator Hydraulic System Main Pump (Destroke Pressure) - Test and Adjust Caterpillar

Introduction

Pump destroke pressure is the control pressure from the pump control to the pump destroke servo in the pump regulator. Each pump must be isolated and tested separately. The pump that is not being tested must remain at low-pressure standby. In order to isolate one of the pumps, disconnect the power shift signal from the pump that is not being tested.

Required Tools

Front Pump

1. Position the machine on level ground.

2. Stop the engine.

3. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".

4. Attach 311-1362 Vacuum Cap onto the hydraulic tank. Attach an air supply hose onto the assembly. Apply 276 to 414 kPa (40 to 60 psi). This procedure will pull a vacuum on the hydraulic system.

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Illustration 1	g02173742
(F) Service connector

5. Connect Cat ET to service connector (F). Cat ET is used to enter a fixed power shift pressure.

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Illustration 2	g02173740
Main pumps (left side view) (1) Pressure tap (front pump delivery pressure) (2) "M1" port (front pump) (3) 3J-1907 O-Ring Seal (4) 6V-3965 Fitting As (5) Plug

6. Remove plug (5) from port (2) .

7. Install fitting (4) and seal (3) in port (2) .

8. Connect a 34,450 kPa (5,000 psi) pressure sensor to fitting (4) at port (2). This sensor is used to monitor the front pump destroke pressure.

9. Connect a 41,368 kPa (6,000 psi) pressure sensor to pressure tap (1). This sensor is used to monitor front pump delivery pressure.

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Illustration 3	g02173741
Main pumps (right side view) (6) Rear pump regulator (7) Pressure tap (power shift pressure at the front pump) (8) 148-8353 Elbow Assembly (9) Line (power shift pressure to rear pump regulator) (10) Front pump regulator

10. Disconnect line (9) from elbow (8). Install 6V-9829 Cap on elbow (8) .

11. Install 6V-8397 O-ring Seal and 6V-9508 Face Seal Plug in the open end of line (9) .

12. Remove 311-1362 Vacuum Cap and install the filler plug for the hydraulic tank.

13. Connect a 3,445 kPa (500 psi) pressure sensor to pressure tap (7) on the front pump regulator. This sensor is used to monitor the power shift pressure at the front pump.

Rear Pump

1. Position the machine on level ground.

2. Stop the engine.

3. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".

4. Attach 311-1362 Vacuum Cap onto the hydraulic tank. Attach an air supply hose onto the assembly. Apply 276 to 414 kPa (40 to 60 psi). This procedure will pull a vacuum on the hydraulic system.

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Illustration 4	g02173742
(F) Service connector

5. Connect Cat ET to service connector (F). Cat ET is used to enter a fixed power shift pressure.

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Illustration 5	g02173743
Main pumps (left side view) (3) 3J-1907 O-Ring Seal (4) 6V-3965 Fitting As (5) Plug (11) Pressure tap (rear pump delivery pressure) (12) "M1" port (rear pump)

6. Remove plug (5) from port (12) .

7. Install fitting (4) and seal (3) in port (12) .

8. Connect a 34,450 kPa (5,000 psi) pressure sensor to fitting (4) at port (12). This sensor is used to monitor the rear pump destroke pressure.

9. Connect a 41,368 kPa (6,000 psi) pressure sensor to pressure tap (11). This sensor is used to monitor rear pump delivery pressure.

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Illustration 6	g02173744
Main pumps (right side view) (6) Rear pump regulator (10) Front pump regulator (14) Pressure tap (power shift pressure at the rear pump) (15) 148-8353 Elbow Assembly (16) Line (power shift pressure to rear pump regulator)

10. Disconnect line (16) from elbow (15). Install 6V-9829 Cap on elbow (15) .

11. Install 6V-8397 O-ring Seal and 6V-9508 Face Seal Plug in the open end of line (16) .

12. Remove 311-1362 Vacuum Cap and install the filler plug for the hydraulic tank.

13. Connect a 3,445 kPa (500 psi) pressure sensor to pressure tap (14) on the rear pump regulator. This sensor is used to monitor the power shift pressure at the rear pump.

Test and Adjust

The front pump and the rear pump must be tested separately. Use the following procedure in order to test and/or adjust each pump.

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Illustration 7	g00623792
Line relief valve (bucket cylinder rod end)

1. Reduce the pressure setting of the line relief valve for the bucket cylinder rod end.

   1. Mark the initial position of the adjustment screw in order to return the screw to the original position.

   2. Loosen the locknut on the line relief valve.

   3. Turn the adjustment screw counterclockwise by FOUR turns.

2. Start the engine.

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Illustration 8	g02173746
Monitor and keypad (A) Engine speed (B) Gain/Response (C) AEC switch (D) Gain/Response switch

3. Place the machine controls at the following settings:
   • Engine speed dial "1"

   • AEC switch OFF

   • Gain/Response "AVS" (normal mode)

   Refer to Testing and Adjusting, "Engine Performance - Test (Engine Speed)" for engine rpm settings.

4. Place the hydraulic activation control lever in the UNLOCKED position.

5. Increase the hydraulic oil temperature to 55° ± 5°C (131° ± 9°F).

6. Use Cat ET in order to enter a fixed power shift pressure of 1870 kPa (271 psi).

   1. Use the override parameters of the engine control module in order to set the power shift pressure.

   2. Begin by entering a value of approximately 0.475 Amps in Cat ET.

      Note: Always monitor the actual power shift pressure reading at the power shift pressure port. The actual power shift pressure must be 1870 kPa (271 psi) on the pressure indicator.

7. Slowly move the joystick for the bucket to the BUCKET OPEN position. Hold the joystick for the bucket in the full BUCKET OPEN position.

   Note: Do not relief the valve for more than 10 seconds.

8. Check the pressure readings on the following pressure sensors: the pressure sensor for power shift pressure, the pressure sensor for pump delivery pressure and the pressure sensor for destroke pressure. The pressure sensors should register the following readings:

   Power shift pressure ... 1870 kPa (271 psi)

   Pump destroke pressure at the "M1" port ... 0 kPa (0 psi)

   Pump delivery pressure (maximum) ... 10800 kPa (1566 psi)

9. Observe the pressure reading for the pump destroke pressure at the "M1" port and the pressure reading for pump delivery pressure while the adjustment screw of the line relief valve is turned clockwise. Record the pump delivery pressure when the pressure reading for the pump destroke pressure at the "M1" port begins to increase.

   Note: The pump destroke pressure at the "M1" port should increase when the pump delivery pressure is approximately 11000 kPa (1595 psi).

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   Illustration 9	g02173745
   Main pump regulators (right side view) (6) Rear pump regulator (10) Front pump regulator (17) Horsepower adjustment screw (18) Locknut

   1. If the pump destroke pressure at port "M1" increases before the pump delivery pressure reaches 13790 kPa (2000 psi), adjust the destroking pressure point. Loosen locknut (18) and turn horsepower adjustment screw (17) counterclockwise. This adjustment will cause the pump to begin destroking at a higher pump delivery pressure. Tighten locknut (18) .

   2. If the pump destroke pressure at port "M1" increases after the pump delivery pressure reaches 11000 kPa (1595 psi), adjust the destroking pressure point. Loosen locknut (18) and turn horsepower adjustment screw (17) clockwise. This adjustment will cause the pump to begin destroking at a lower pump delivery pressure. Tighten locknut (18) .

      Note: To avoid excessive leakage during the adjustment of the horsepower adjustment screw, loosen locknut (18) only far enough so that horsepower adjustment screw (17) can be turned.

      Note: Always make the pressure adjustment on the pressure rise.

10. After setting the pump destroke pressure to 11000 kPa (1595 psi), reduce the line relief valve pressure setting and repeat Steps 7 through 9 in order to verify that the pump destroke pressure remains at 11000 kPa (1595 psi).

11. After the pump destroke pressure has been tested and/or adjusted, reconnect all disconnected hoses to the main pump regulators.

12. Check the line relief valve pressure setting for the bucket cylinder. If the pressure setting is not within the specification, adjust the line relief valve. Refer to Testing and Adjusting, "Relief Valve (Line) - Test and Adjust".