Hydraulic system, fault, logic reasoning, diagnosis method

1. logical diagnosis

Hydraulic fault analysis is a logical thinking process, is a use of the concept and nature to explore the hydraulic fault by judging and reasoning process, and all the internal links: the concept is the essential attribute of reflecting things to reflect things form of thinking. In logical thinking, the concept is the basic elements of judgment and reasoning, judgment is posed by the concept of things is concluded form of thinking and reasoning is composed of one or several known judgment (premise) launched a new judgment conclusion), argumentation is a real judgment to prove the authenticity of the thinking process of another judgment.

In fact, hydraulic fault analysis, as a rational thinking, people consciously or unconsciously adopted a logical way of thinking. But there are also many problems, such as ambiguity of concepts, errors in judgment and reasoning, and so on. It is necessary for fault analysts to try to make the concepts clear and to standardize the methods of judgment and reasoning. Logic inference is a simple and reliable method for diagnosing the faults of hydraulic system.

In order to avoid the analysis of logical errors in all kinds of fault, fault diagnosis personnel should pay attention to the following points: the logical analysis requires knowledge and experience enough, master all kinds of typical hydraulic failure, so as to find the basis for evaluation at any time in the process of analysis. Logical analysis requires sufficient field information, although some conclusions can be indirectly introduced by using logical analysis methods, but if the amount of information is too small, logical analysis is difficult to carry out. The logic analysis process must be extremely careful, cannot neglect to omit the related factor. Do not take the conclusion of subjective judgment as an objective fact without verification. Good at summing up conclusions from cases, and flexibly grasp the general and special relationship. The good from different perspectives on the same problem was investigated in different ways, if the investigation conclusion is not consistent, can make a further study on the difference. And continuously improve the ability of logical thinking, do the thinking process correctly, on condition of variation in sensitivity, the mind can accommodate a large amount of information, and can clear and orderly organization, call and deal with these information.

Example of hydraulic fault logic diagnosis for 2.TL-360 crane

Have a Nissan TL-360 tadano crane, a hoisting operation arm when in the abnormal sound after the crane suddenly fall. Since then, although the lifting arm unloaded a small amount of lifting, but then fell back. Preliminary judgment, the fault may occur in variable amplitude hydraulic circuit.

As shown in Figure 8-6, the variable cylinder 6 and 7 are controlled by manual reversing valve. The double gear pump 2A supplies both the variable amplitude cylinder and the telescopic cylinder. The dual gear pump 2B supplies oil to the support leg. The maximum working pressure of the pump 2a is limited by the relief valve, and the setting pressure is 17.5Mpa. The balance valve is installed at the bottom of the hydraulic cylinder, locking and preventing the speeding drop, and the control oil circuit is provided with a variable flow valve. If the boom is unstable, the throttle opening of the valve can be adjusted.

When the engine is running properly, it can be concluded that the fault is caused by the problem of the variable hydraulic circuit.

According to the principle of variable amplitude hydraulic circuit and the analysis of the fault phenomenon, it may be a sudden fault, or it may be caused by insufficient pressure.

Although the lifting arm has a small amount of lifting, it immediately drops back, indicating that the jib is in a state of being unable to lift.

Accordingly, it is possible to first eliminate the possibility of a malfunction of the balance valve.

Because the fuel tank is normal, it is possible to introduce the cause of the failure in the system.

Possible reasons are as follows: double gear pump wear caused serious leakage of oil pipeline, or pump suction air; the relief valve failure caused by pressure on the 8, not to; the amplitude hydraulic cylinder 6, 7 oil; the manual valve wear.

The gear stay 2a is not only supplied with the same variable cylinder, but also with the telescopic cylinder for the fairy. The maximum pressure of the expansion loop and the variable amplitude loop is limited by the overflow valve 8. The operation of the telescopic control valve realizes the normal operation of the telescopic work of the lifting arm, so that two possible failure reasons are excluded.

Manual reversing valve wear is a wear fault, and relative to the hydraulic cylinder, the frequency of its failure is much smaller. For this reason, the hydraulic cylinder shall be checked first.

Take the tubing in the upper and the 7 cavities of the variable cylinder 6 to disassemble at the joint, release the remaining oil, and then lift the lifting arm. At this point, a large number of hydraulic oil flow from the upper cavity pipe joints, and proved that the fault is caused by leakage of hydraulic cylinder.

In the dismantling of luffing cylinder 6, 7, O found on the piston ring and piston rod seals are normal; then check the cylinder roundness and cylindricity error, the 3mm roundness one hydraulic cylinder at the lower end of the cylindricity error, the maximum value of 6mm. So, can determine, there may be operations generated in the process of the hydraulic impact, causing the safety valve opening lag, the instantaneous pressure rises too fast, and the shortcomings of the original amplitude cylinder on (severe deformation caused by the disrepair), resulting in seal failure.

Remove a variable cylinder from another crane with the same type of work, and when the test machine is installed, the fault will disappear.

An example of hydraulic fault logic diagnosis for 3.YA32-200 four column universal press

A YA32-200 four column universal press hydraulic system as shown in Figure 8, 7, fault symptoms mainly, cylinder down fast normal, high pressure suppression pressure is not high. The possible causes of the failure are: (1) hydraulic pump wear, serious internal leakage, low output. Remote pressure regulating valve 5 and overflow valve 4 damage, not high pressure. Fill the liquid valve 14 damage, the formation of oil drain. The main cylinder 6 is damaged to form internal leakage.

Because of the difficulty of removing the master cylinder, the method of indirect demonstration is used to demonstrate the authenticity of symptoms caused by leakage in the master cylinder. Here, the basic idea is to verify that the other 3 possible causes are not present, and then infer the damage to the hydraulic cylinder.

It is proved that the hydraulic pump 1, the relief valve 4 and the remote pressure regulating valve 5 are not related to the symptoms. The operation process is as follows: 5, 4 and 18 of the valve closed, the electromagnet 4YA powered ejection cylinder top executive action, adjust the relief valve 20, observe the pressure gauge B, pressure up to 32Mpa (pump rated pressure) the pump and the pressure regulating valve is normal.

It proves that the filling valve has nothing to do with the symptoms. The operation process is as follows: the 1YA electromagnet system performs main cylinder press action, observation of liquid tank oil return, observation results showed that there was no obvious oil return, the filling valve is normal, no accidental opening.

The two conclusion is that, in the process of the main pressure cylinder pressure in the pump and the pressure control valve can ensure the normal working pressure filling valve there is no oil drain, so from the hydraulic pump to the master cylinder pressure oil passage, the clearance between the piston and cylinder cylinder only can discharge high pressure oil put under the pressure of increasing pressure.