Analysis of the Causes of Asynchronous Movement of Crawler Cranes and Troubleshooting

Crawler cranes often experience a phenomenon where the tracks on both sides do not move in sync, that is, they deviate. If the phenomenon is not very obvious, it should be normal because there are certain differences between the structural components and the hydraulic components on both sides. As long as it is controlled within the allowable range stipulated by the national standard, the deviation is qualified. If the deviation is severe, it is a fault and should be dealt with promptly. The allowable deviation of crawler cranes as stipulated in the national standard (GB/T14560-93) : The deviation of the crane during travel (trajectory deviation of 20 meters forward or backward) shall not exceed 25cm (as shown in Figure 1)

Due to the large number of components in the traveling oil circuit, there are many factors causing asynchronous movement, making it difficult to identify the true cause. Moreover, the fault phenomena also vary. Generally, there are two types: deviation in only one direction when moving forward or backward, and deviation in one direction when moving forward or backward. Based on the principle, analyze one by one according to the size of the failure rate.

Working principle (as shown in Figure 2) : When operating the pilot handle (sequence 7), the pilot handle (sequence 7) supplies pressure oil to the hydraulic oil port of the main directional control valve (sequence 4), pushing the main valve core to change direction. The working port of the main valve opens, and the main oil circuit enters the brake valve (sequence 2) through the central rotary body (sequence 3). After throttling at the hydraulic control port of the brake valve, the main valve core of the brake valve is pushed open to provide pressure oil to the motor (sequence 1). At the same time, the pilot handle supplies pressure oil to the brake through the shuttle valve (sequence 5), opens the brake, and the motor starts to operate, thereby driving the traveling reducer to rotate and achieving the traveling of the crawler crane. The brake valve serves functions such as hydraulic braking when the vehicle stops and speed limiting when going downhill. From the perspective of the hydraulic system schematic diagram, any malfunction of several components such as the motor, brake valve, main valve, shuttle valve, center rotary body and pilot handle will cause the movement to deviate.

I. Fault phenomenon: Deviation occurs in only one direction when moving forward or backward

Phenomenon description: It always deviates in one direction when moving forward but does not deviate when moving backward, or it always deviates in one direction when moving backward but does not deviate when moving forward.

Troubleshooting method: Check the following components in sequence from the highest to the lowest failure rate

1. Check the brake valve

Method 1: Swap the pipelines that control the forward and backward directions at the oil inlet of the brake valve. If the deviation direction changes, rule out the factor of the brake valve. If the deviation direction does not change, disassemble and inspect the brake valve to check whether the valve core is stuck by foreign objects. Whether the throttle port inside the valve is blocked or not can cause the valve core to not act properly, resulting in a small valve port opening and a small flow of hydraulic oil, which leads to a slow speed on one side.

Method 2: Connect a pressure gauge to each of the oil inlet (P port) of the main valves that control the left and right travel, and conduct a travel test to measure the pressure on both sides. If the pressure difference between the two sides is not significant, it indicates that the brake valve is not faulty. If the pressure on the slower side is significantly higher than that on the faster side, it indicates that the valve core on the slower side is not operating properly and the oil flow is not smooth. Disassemble and inspect the brake valve. However, if the pressure on the side that moves faster is significantly higher, the brake valve fault should be ruled out.

2 Check the rotating body of the inspection center

Swap the pipelines that control the forward and backward directions at the oil inlet of the central rotating body. If the deviation direction does not change, disassemble and inspect the central rotating body. Check whether the seal is damaged and whether there are sand holes at the oil port, etc. If the deviation direction changes, it is not due to the central rotation body factor.

3 Check the pilot handle (Sequence 7)

Method 1: Test the pressure of the corresponding pilot oil port. If the pressure on the slower side is significantly lower than that on the faster side, the control handle is damaged. Check if there is any dirt blocking it. Disassemble and adjust the pilot valve handle to observe whether the ball joint is damaged and whether the spring is normal.

Method 2: Swap the pilot pipeline that controls the forward and backward directions at the main valve control oil port. If the deviation direction changes, it indicates that the control handle is clogged or damaged.

4 Check the shuttle valve

Disassemble the shuttle valve to check if there is any contamination blocking it. Inspect whether the steel ball of the shuttle valve is stuck or damaged, and whether the valve seat is leaking or damaged.

5 Check the main valve (structure as shown in Figure 3)

Method 1: Test the pressure at the hydraulic control ports at both ends of the main valve. If the pressure on the side with slower movement is significantly higher than that on the side with faster movement, check the pilot control port on the side with slower movement to see if there is any dirt blocking or leakage. Whether the reset spring of the main valve core is stuck or damaged.

Method 2: Swap the pipelines that control the forward and backward directions at the oil inlet of the central rotating body. If the deviation direction changes, it is due to the main reversing valve. Disassemble and inspect the main reversing valve.

Ii. Fault Phenomenon: Both the forward and backward movements deviate to one side

Phenomenon description: The walking motor that is always on one side whether moving forward or backward has a slow traveling speed. Troubleshooting method: Check the following components in descending order of failure rate: walking motor, walking brake valve, main reversing valve, pilot handle, center rotary body, shuttle valve, main pump.

1. Walking motor

Method 1: The main fault of the motor is a large internal leakage. You can open the oil drain port of the motor to check the internal leakage. Normally, the oil should overflow slowly. When the oil starts to spray, the internal leakage is too large.

Method 2: The most intuitive approach is to swap the pipelines at the left and right oil inlets of the walking motor. If the deviation direction remains unchanged, it is determined that the motor is faulty. If the deviation direction changes, the motor fault is ruled out.

2 Walking brake valve, main directional control valve

The inspection methods for the walking brake valve and the main directional control valve are basically the same as those listed in the fault section. The difference lies in that, in addition to checking whether the valve core is stuck by foreign objects and whether the throttle port inside the valve is blocked, it is also necessary to measure whether the processing tolerance of the valve stem and the valve seat is within the tolerance range. If it exceeds the tolerance, the internal leakage will be large, causing a large difference in the flow of the two motors on both sides, thus resulting in deviation.

3 Pilot handle, central rotating body, shuttle valve

The inspection methods for the pilot handle, the central rotating body and the shuttle valve are basically the same as those listed for the faults

4 Main pump.

The probability of problems occurring with the main pump is relatively low, but the factors that cause the problems cannot be ruled out. The main issue is severe internal leakage, which causes different fuel supply on both sides of the track.

Due to the numerous reasons for the asynchronous movement of crawler cranes, only by being familiar with the working principle of the system and understanding the structure of hydraulic components can faults be analyzed, judged and eliminated in a targeted and correct manner, and problems be solved quickly.