The removal of the boom of the excavator and the slow failure of the left turn

One of the original construction of the Shanghai R942 hydraulic excavator factory production, the following failures in Construction: Boom lifting weakness, left turning slowly; when the continuing operation of 0.5h, a temperature rise, the arm cannot be promoted, and almost can not turn left turn. Analysts believe that, in the other normal action of main pump and main relief valve is in good condition, caused by the boom to possible reasons: the main control valve spool and valve wear leads to the gap is too large, resulting in large leakage; overload valve and fill oil valve damage or low voltage arm cylinder; seal damage within the vent; pilot control circuit fault.

We in temperature 45~55 degrees, one by one of the above 4 reasons were examined, the results of the first 3 items were found no problem, but in pilot oil, found control leakage lifting boom pilot valve handle; the engine is running at high speed, the measured oil pressure lifting boom pilot only 2MPa (standard value of 3.3MPa), in the pilot oil so low under the control of the main control valve cannot be pushed to the maximum travel position, so the system flow and pressure are not enough, resulting in inability to enhance the boom. After the pilot valve is broken, the O sealing ring in the piston sleeve has been damaged. After the new test machine, the arm lifting has returned to normal.

The main reason for the slow phenomenon of left rotation is that the main control valve is faulty or the pilot oil circuit is abnormal. Itemized examination found that the overload valve on the pilot valve cone valve wear serious (about 0.10mm of the grinding mark). After grinding on the high precision cylindrical grinding machine, the left and right turn are normal in the machine test.