Four common faults and their diagnosis in the hydraulic brake system of a wrecker

The core prompts the hydraulic system to have the early signal to have the breakdown, may carry on the examination in time according to these signals, eliminates the hidden trouble which may have the breakdown, reduces the unnecessary loss, prolongs the service life of the hydraulic system. Before the hydraulic system fails, there will be an early signal, but it is not easy to accurately diagnose the location of the fault.

The failure of the hydraulic system is preceded by a signal, which can be checked in time according to these signals, to eliminate possible hidden troubles, reduce unnecessary losses, and extend the service life of the hydraulic system.

Before the failure of the hydraulic system, there will be early signals, but it is not easy to accurately diagnose the location of the failure, which is exactly what the hydraulic technicians are trying to solve. Because the factors of the failure of the hydraulic transmission device are often many and complex, sometimes the latency of the fault is long and hidden deeper, it is not easy to be discovered or hidden, so we must pay close attention to the random performance and observation of the transmission system. In combination, it is possible to accurately diagnose where the fault will occur.

In general, the hydraulic system of the wrecker is assembled from components and systems, so long as the impurities are strictly controlled to enter the system and the cleanliness of the oil passages and hydraulic lines of the oil passage blocks and the hydraulic oil are maintained, the hydraulic system is unlikely to fail. of. However, if insufficient attention is paid to a certain link or the hydraulic components are not clean, impurities will sooner or later occur in the system. According to our many years of practical experience and customer feedback, the 80% of failures in hydraulic transmissions are caused by hydraulic oil contamination, and 20% are caused by poor mechanical quality and lack of operational knowledge. The following examples are analyzed from several aspects:

1, the poor quality of hydraulic parts will appear fault signal

During the operation of the hydraulic transmission system, the pressure gauge is an important direct-reading instrument for observing the operation quality. Therefore, you should always monitor the change in the indicator value of the pressure gauge. We have found that a hand truck has a rapid drop in the pressure gauge pointer of 4-8 mpa during the factory test, and all the actions cannot be performed at the end. This failure signal is very sudden. General pressure valve has a gradual process when there is a problem. If the pressure is stuck, the pressure will drop to zero, and it will not fall in stages. It is very unusual for such a signal to appear. Therefore, we first inspect the overflow valve and pull out the overflow valve spool. When no abnormality is found in the inspection valve, we continue to carefully observe the valve body cavity, and finally we find that there is an irregularity of about 1mm on the inner wall of the low pressure chamber. The hole is communicated with the high pressure chamber. Why does this phenomenon occur? After analysis, due to the presence of sand or loose spots in the casting process, the valve body was not exposed during machining, and the valve was not found in the factory due to short time. After loading the car, the pressure of the pressure and vibration of the whole vehicle action, the pressure oil in the high-pressure chamber breaks through a very thin layer of the surface, and communicates with the low-pressure chamber, so that no pressure is formed when the pressure is applied.

2, hydraulic oil pollution will appear fault signal

When the wrecker's hydraulic system is working normally, the hydraulic cylinder operates with a balanced and uniform speed. If one of the following conditions is found, it is an early signal that a fault will occur.

(1) There is a change in the forward speed of the hydraulic cylinder, or it may be faster or slower.

(2) The hydraulic cylinders exhibit irregular vibration during advancement.

(3) When a command is issued to the hydraulic cylinder, the operation is delayed or irregular.

(4) In normal operation, a screaming or abnormal harsh sound is suddenly generated.

When one of the above conditions occurs, it can generally be considered an early signal of hydraulic oil contamination. Of course, this type of phenomenon is not always the same, sometimes instantaneous, sometimes slightly, and it has no obvious immediate impact on the operation of the wrecker, so it is easily overlooked. In order to avoid failures that can cause wreckers to fail to work, we should promptly and thoroughly remove impurities from the hydraulic system. If the oil is discharged (extracted) out of the filter, clean the tank and suck and return the oil filter and the pipeline oil block.

3, mechanical reasons will cause failure

We have found that there is a 3-ton Qingling chassis wrecker multi-way valve with electromagnetic valve, all actions are electronically controlled, a group of multi-valve control 4 cylinders and 1 motor, click on each action The button is all right and the hydraulic system is very simple. It has been normal since it was put into use. No problems occurred in the operation. However, after using it for two years, one of the buttons of one action has to be pressed twice. This signal indicates that the hydraulic system has failed, but it has not caused the attention of the staff. Even if it does not respond after three or more times, the hydraulic cylinder will not work. After inspection, the fault occurred on the solenoid reversing valve. The screws that installed the electromagnets were loose, which caused the displacement of the solenoid valve core to change. The spool failed to act and the hydraulic oil could not reach the hydraulic cylinder. After tightening the screws, the fault was eliminated.

4, glitches will cause failure

A 20-ton wrecker for a certain unit has experienced such a fault in the process of being used soon after leaving the factory: After the oil pump is started, the multi-way valve and the throttle are operated many times, and neither the hydraulic cylinder nor the motor operates. Check the linkage mechanism of the multi-way valve and found no detachment phenomenon. The hydraulic pump has no problem after inspection. I do not know where the last, we will remove the multi-valve valve safety valve, found that the safety valve is a spool-type valve structure, the burr can not be reset, the spring can not overcome the clamping force. After the burr is removed, the safety valve is cleaned and reinstalled on the multi-way valve to start the hydraulic pump and the commutation is working properly.


Through the above example analysis, we believe that sometimes the breakdown of the wrecker's hydraulic system is unavoidable, and the solution is usually relatively simple. However, if there is no accumulation of usual experience, it is not easy to handle it. Therefore, when we use a wrecker, especially its hydraulic system, we must be alert and observe carefully. As long as the small problems are removed in time, the big problems can be overcome in the bud.


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