Strategies and techniques of hydraulic fault diagnosis -- finding fault characteristic information

The causal relationship between the formation and development of hydraulic fault has alternating and overlapping characteristics, in order to save troubleshooting time, reduce the workload of disassembly process, disassembly and avoid the adverse effects, should have the choice, internal condition of focus, in order to check the hydraulic device. Fault diagnosis based on the fault must be observed on the surface of hydraulic symptoms, according to the related criteria, to infer the probability of each fault size, then according to the specific circumstances of the scene, make analysis and evaluation further carefully on the hydraulic device.

1. overview of fault feature information

Although different causes can cause a similar symptom, they have different forms of expression. In addition, there are obvious differences between the causes of the different symptoms and the same symptoms. We call characteristic information about the different manifestations of symptoms and the information peculiar to different causes. To find out the corresponding features of the various possible causes of the fault, we find a sign to distinguish them, so that when the system has a symptom, we can find the real cause of the fault according to the characteristic information.

Characteristic information can be represented by individual parameters. When the problem is complex, it is necessary to synthesize a series of parameters to form the characteristic information of the cause of the fault.

2. classification of hydraulic failure reason information

      There are three kinds of characteristic information for different reasons of hydraulic failure.

(1) the difference of symptoms caused by different reasons the same symptoms, their manifestations are different, the difference in time characteristics, symptoms of mechanical characteristics, influence scope, intensity and different background etc.. For example, the same is the noise of the vane pump, the damage of the rotor in the pump is obviously different from that caused by the absorption of air. The former is periodic, the latter is obvious when the system is loaded, and the unloading operation disappears. Again, with the hydraulic cylinder moves, there are not any position in action, also have no action on the endpoint, and during a certain point action; in the no-load condition can drive load does not move, also with or without load are not action there are situations; only in, no return, also can only return not in the situation, also has and cannot realize the situation; sometimes good and bad, there has not been the case in the manual; no action, but also in the case of automatic action. There is no doubt that these different situations correspond to very different causes of failure.

The fault analysis must make a deep and detailed observation and classification of the symptom itself, clarify its characteristics and investigate its causes.

(2) there are different reasons, with other anomalies due to a fault caused by a certain symptoms at the same time, will also bring some other anomalies, they reflect the specific circumstances of failure from different sides. In determining the cause of the failure, attention must be paid to the exception of symptoms and to link them to symptoms. For example, the hydraulic system appears crawling, which may be due to oil mixed with human air, hydraulic pump wear, flow valve can not adjust the pressure and load rail resistance inequality. The abnormal phenomena caused by the different causes of the fault are as follows: if there is a crawl phenomenon, and the increase of oil bubbles in the oil tank, it can be considered that the cause of the trouble is that the oil is mixed with air. If there is crawling phenomenon, and overflow valve overflow flow increases, the pressure is not high, can be considered as overflow valve failure caused by crawling.

If there is crawling phenomenon, and the hydraulic cylinder can be observed on the track of abnormal friction marks, can be considered as uneven rail resistance caused by crawling.

(3) the abnormal change of state structure of hydraulic components hydraulic components of structure state, caused by the hydraulic system performance or other problems, the fault reason also has a variety of possibilities, the decomposition of hydraulic components by removing, observing and testing its internal condition, can distinguish the true cause of failure. For example, the one-way valve has a serious internal leakage, bite can be the sealing surface of the body wear, valve leakage caused by, the possible reasons are: the valve sealing surface wear, valve core sealing surface wear, dirt retention in the sealing surface. To find out what caused the leak, only to open it for inspection. When the external parts of the component are assembled incorrectly or the connection is not good, the surface observation of the component structure can also find out the cause of the fault. For example, for the XF sequence valve (Fig. 9-1), when it does not control in sequence, the possible cause is that the main valve core is stuck at the closed position, and the leaking tubing is attached to the outlet pressure P2 side. The former to open the valve to check to determine, the latter only need to connect the status of the oil pipe surface observation, you can draw conclusions.

According to the general instructions or related equipment may cause hydraulic maintenance books found the symptoms of, through mechanism analysis and logical analysis detailed diagram of the system, operation table, component specifications and other information, to find out the fault feature information corresponding to the.

3. die casting machine system, non pressurization fault reason, characteristic information analysis example

The hydraulic system of a 1125A horizontal metal die casting machine is shown in figure 9-2.

The equipment type, there is a ~ pressurization process, 2YA, 3YA and 5YA when the electromagnet power, oil pressure valve, I valve, one-way valve, electro-hydraulic valve II into the pressurizing cylinder cavity 5 and plunger cylinder cavity after 2 booster (liquid pressure chamber 3), when closing force reaches the specified value, the electric contact pressure gauge signal, performing injection.

The symptom of failure is that the pressure can not be increased when the pressure is increased, that is, the pressure of the chamber 3 can not be raised.

There are 7 possible causes of this symptom. The liquid filled valve W is not sealed properly, which makes the chamber 3 pressure relief. The electromagnetic valve m work is not reliable, so that the liquid filled valve is not closed. The tubing connected with the cavity 3 is loose or ruptured. The plunger cylinder or crack, sand holes, porosity and other defects caused by pressure relief each other. The seal between the cylinder and the plunger cylinder is damaged and the chamber 3 is released from pressure. The sealing between the plunger and the plunger is damaged, causing 3 cavity pressure relief. The seal is broken between clamping cylinder and plunger, causing 3 cavity pressure relief.

According to the various aspects of the hydraulic circuit, to determine the symptoms of different reasons for failure, as follows:

The characteristic information of the utility model is that when the chamber 1 is pressurized, the liquid filling valve III return pipe has an oil outflow, and the cavity 2 uses kerosene as a sealing cone to check the leakage of the liquid filling valve, and obvious leakage occurs.

The characteristic information of the utility model is that when the booster is checked, the return pipe of the electromagnetic valve III can not be seen, and the liquid flow out of the liquid filling valve (indicating no reversing) during the switching process can be seen, and when the cavity 2 is pressurized, the oil return valve of the liquid filling valve is flowed out.

The corresponding feature information is related to the oil spill or tubing joints.

In addition to the abnormal pressure, other movements are abnormal, and the motion will be out of control and the pressure will not go up.

The characteristic information is that when pressurizing, the gap between the cylinder and the plunger cylinder has an outflow of oil.

The corresponding feature information is increased while the pressure is not high, but there is still a certain pressure, cavity 3 and cavity 2 and 5 cavity pressure

Again, this pressure is the same as the pressure relief valve. When the pressure of the relief valve is changed, the pressure of the chamber 3 is correspondingly changed

The corresponding feature information is pressurized when the electro-hydraulic valve and the oil return pipe of oil well (this is the 3 booster cavity leak out of oil, in good sealing without this phenomenon).

According to the relation between the above-mentioned characteristic information and the cause of the fault, the real reason of the pressurization fault can be found quickly and accurately on the spot.