I. Core Pressure Parameters and Test Positions
The pressure of the hydraulic system of the Caterpillar excavator needs to be measured through a dedicated test interface. The main parameters and positions are as follows:
The test interface for the output pressure of the main pump (working hydraulic system) is located at the high-pressure oil pipe joint of the main pump (usually with a quick coupling).
Normal range: 300-350 bar (Specific models may vary; for example, the main pump pressure of the 336D2 model is 343 bar).
The pilot control pressure (operating valve control) test interface is located on the pilot pump outlet or the pilot oil circuit block of the main control valve.
Normal range: 35-40 bar.
The rotary pressure (rotary action) test interface is located at the oil inlet of the rotary motor.
Normal range: 250-280 bar (no-load); 300-320 bar (load).
The walking pressure (track drive) test interface is located at the oil inlet of the walking motor.
Normal range: 300-330 bar (on hard ground) 280-300 bar (soft floor).
Ii. Testing Tools and Procedures
Tool preparation: Hydraulic pressure gauge set (with quick couplings, range 0-400 bar).
Adapters suitable for Caterpillar models (such as M18×1.5 threaded interfaces).
Gloves, safety glasses and cleaning cloths.
Operation steps: Shutdown preparation: Park the excavator on a flat ground, then turn off the engine and release the system pressure (move the control lever several times).
Connect the pressure gauge: Clean the test interface, install the adapter and connect the pressure gauge.
Start-up test: Start the engine and let it idle.
Operate the corresponding action (such as lifting the boom) and observe the pressure gauge reading.
Record the pressure values at idle speed, medium speed and high speed.
Data comparison: Compare the measured values with the standard values in the maintenance manual. If the deviation exceeds ±10%, maintenance is required.
Iii. Common Pressure Abnormalities and Their Handling
The reasons for the low pressure of the main pump: wear of the main pump, malfunction of the relief valve, and contamination of the hydraulic oil.
Treatment: Replace the internal parts of the pump, clean the relief valve, and replace the hydraulic oil and filter element.
Reasons for insufficient pilot pressure: pilot pump failure, filter element blockage, pipeline leakage.
Handling: Inspect and repair the pilot pump, replace the filter element, tighten or replace the pipeline.
The reasons for large pressure fluctuations are: malfunction of the main pump regulator, air leakage in the suction pipe, and abnormal viscosity of the oil.
Handling: Adjust or replace the regulator, check the seal of the oil suction pipe, and replace the recommended grade of hydraulic oil.
Iv. Safety Precautions
Protective equipment must be worn during the test to avoid injury from high-pressure oil spray.
Do not remove the oil pipe when the engine is at a high temperature to prevent burns.
If abnormal pressure is accompanied by abnormal noise or slow movement, the machine must be stopped immediately for maintenance.
Note: The pressure standards of different models of Carter (such as 320, 336, 349, etc.) may vary slightly. It is recommended to refer to the maintenance manual of the corresponding model. If you have no experience, it is recommended that you contact an authorized Carter service provider for professional testing.
