The reasons for the excavator's weak turning power

A Komatsu PC400-6 excavator, after a major overhaul of its hydraulic main pump, could move in a straight line or turn in place normally. However, when operating either of the walking control rods alone, it experienced a lack of power when turning.

The test results show that the speed of the working device, the overflow pressure and the walking overflow pressure are all within the standard range. However, when operating either walking control lever alone, the left and right tracks move forward and backward in the same way, and the walking speed is significantly slower.

When the machine is in motion, the main oil circuit is in a split state, and the LS oil circuit is also in a split state. That is, the hydraulic oil from the front pump is sent to the left walking motor, while the PLS2 oil pressure generated by the left walking main valve core is only fed back to the front pump. The hydraulic oil from the rear pump is transmitted to the right-walking motor, while the PLS1 oil pressure generated by the right-walking main valve core is only fed back to the rear pump.

The inspection proves that when the two LS oil pipes fed back to the main pump are connected in reverse (see the attached figure), if a one-way walking turn is performed, the main valve core of the right walking will open under the action of the PPC oil pressure of the right walking, and the main hydraulic oil of the rear pump will be sent to the right walking motor, but the PLS1 oil pressure generated in the main valve core of the right walking will be sent to the front pump. At this time, no LS oil pressure is generated in the main valve core of the left travel, and the LS oil pressure sent to the rear pump is 0. This results in the smallest displacement of the rear pump, which in turn causes insufficient oil supply to the right travel motor and weak travel. When moving in a straight line or turning in place, the magnitudes of the two PLS oil pressures generated at the left and right main valve cores are equal. Even if the LS pipelines are reversed, the LS oil pressures fed back to the front and rear pumps, due to their equal magnitudes, can still make the displacement of the two pumps equal, allowing the machine to move in a straight line or turn in place.

Through fault analysis and then a comparative check, it was found that the two LS oil pipes on the main pump were indeed connected in reverse. After the LS oil pipe was correctly installed, the machine returned to normal.

If the LS oil pipe is connected in reverse, it will also cause another malfunction. The machine operates normally in the combined flow state, but when operating the bucket lever, rotation, boom or bucket separately in the split flow state, the speed is extremely slow and it cannot work. When performing compound actions such as rotation, boom, boom and bucket, the phenomenon is the same as when performing individual actions. However, when performing the actions of the boom, boom, bucket or the combined actions of rotation, boom and bucket, the malfunction will be greatly improved.