The piston motor is the core power actuator of the hydraulic system of Shitian excavator. The causes of its abnormal noise are highly similar to those of hydraulic pump noise, with the core inducements focusing on three categories: air suction & cavitation, abnormal valve plate, and excessive wear of internal components. The troubleshooting logic can be directly applied to the piston motor of energy-saving Shitian excavators. The specific causes and details are explained as follows.

Air Suction Causing Cavitation Noise (Primary Cause)

Excessive air mixed in the hydraulic oil will cause cavitation in the high-pressure area of the motor. The pressure wave generated by cavitation rupture will trigger hydraulic oil oscillation, and eventually form obvious cavitation noise, which is the primary cause of excessive noise in the piston motor of Shitian excavator. The air suction phenomenon is mainly caused by the following three points:

1.Blockage of the oil filter or oil inlet pipeline of the piston motor, or excessively high viscosity of hydraulic oil, will lead to excessively high vacuum at the motor's oil inlet, causing external air to be sucked into the hydraulic oil;

2.Damage to the shaft end oil seal of the piston motor or pilot pump, or loosening and poor sealing at the oil inlet pipeline seal, directly causes air to enter the hydraulic system from the sealing gap;

3.Too low oil level in the hydraulic oil tank of the excavator, the oil inlet pipe of the piston motor is directly exposed above the oil surface, causing direct air suction during operation and a large amount of air entering the hydraulic oil.

 Abnormal Valve Plate Causing Trapped Oil/Improper Unloading Noise

The valve plate is a key component for the piston motor of Shitian excavator to control the inflow and outflow of hydraulic oil and realize unloading. Its structural or installation deviation will directly change the unloading position, cause trapped oil phenomenon, and then generate high noise. The specific problems are divided into three categories:

1.During long-term use of the valve plate, surface wear occurs, or sludge and impurities deposit at the opening of the unloading groove, resulting in a shorter actual effective length of the unloading groove and misplaced unloading timing, forming trapped oil noise;

2.During the maintenance and repair of the piston motor, if the unloading groove is not lengthened after the valve plate is corrected by surface grinding, it will directly lead to the shortening of the unloading groove and cause trapped oil noise;

3.Valve plate installation deviation: if the large unloading groove is not aligned with the high-pressure cavity of the motor during installation, or the sharp angle direction of the unloading groove is inconsistent with the rotation direction of the hydraulic cylinder, it will cause improper unloading and trigger high-frequency noise of the system.

Excessive Wear of Internal Components Causing Flow & Pressure Pulsation Noise

Wear and scratch on the precision matching components inside the piston motor will cause serious internal leakage of the motor, trigger flow and pressure pulsation, and then generate continuous abnormal noise, accompanied by problems such as decreased motor output torque and action hysteresis. The specific wear parts and impacts are as follows:

1.Wear of core mating pairs: Wear and scratch on core mating components such as the cylinder block and valve plate, plunger and plunger hole, intensify the internal leakage of hydraulic oil. The motor will generate obvious flow pulsation when outputting high-pressure and small-flow hydraulic oil, forming high-frequency noise; the deflection angle of the variable mechanism of the pilot system can be appropriately increased to alleviate the impact of internal leakage on the output flow.

2.Wear of control components: Local wear and scratch on components such as the servo valve core and flow control piston will cause pulsation during the piston movement, resulting in large fluctuations in the motor's output flow and pressure, and ultimately strong vibration and noise at the motor outlet; for such faults, the severely worn and scratched components need to be repaired by brush plating and fitting or directly replaced.

Supplementary Troubleshooting for Abnormal Noise of Piston Motor in Energy-Saving Excavators

The causes of abnormal noise of the piston motor in energy-saving Shitian excavators are highly similar to those of the piston pump. On-site troubleshooting can follow the principle of from simple to complex, prioritizing the following basic inspections before gradually checking the internal precision components:

1.First check whether the oil inlet pipeline is damaged, loose, blocked, etc., to investigate whether cavitation noise is caused by air suction;

2.Then check whether the unloading groove of the valve plate has deposition and wear, confirm whether the installation position is correct, and investigate trapped oil noise;

3.Finally, check whether the internal core mating pairs and control components are worn or scratched, and investigate the vibration noise caused by flow and pressure pulsation.