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Common failures of hydraulic system of hydraulic excavator, causes and elimination methods

Aug 05, 2018

A.Two main pipelines of the travel motor burst.

The main reason why two main pipelines (A and B) of the walking motor of the hydraulic excavator often burst is that the valve core of the dual speed valve failed to return in time after the change of speed, resulting in the failure of energy connection between the inlet and the return port and the instantaneous oil pressure. At this point should be:

1. Increase the elastic force of double speed valve spring appropriately. After the control pressure is removed, the valve core can be reset smoothly under the action of spring elastic force. However, it should be noted that the elastic force of spring cannot be simply measured by the method of growth rate and gasket.

2. Grind the dual speed valve to remove the burr, so that the valve core can move freely in the valve body without any lag.

3. Operation should be standardized. For example, the correct operation of shifting gears during a excavator's walk is to stop the excavator before moving at any speed.

B.Walking and running sideways.

When a walking deviation occurs in the excavator, the following section inspection can be made when it is determined that the technical condition of the walking motor is normal and the tightness of the crawler is adjusted correctly.

1. Check the working pressure of the walking hydraulic circuit. Check the slow side first, starting with the combination valve, remove the two tubing on the pressure limiting valve, and plug the oil outlet with the plug. Remove the two running tubing on the other combination valve, start the engine, pull the walking control handle of the combination valve with A plug, observe whether the oil pressure meets the requirements, and observe the A of the other combination valve (the pressure limiting valve) and whether there is oil flow out of the B hole. If the oil pressure is normal and the A and B holes of another combination valve have no oil flow out, it can be considered that the failure is not the combination valve.

If the oil pressure does not reach the normal value, it indicates that the internal leakage is serious. If the A, B holes of another combination valve have oil flow out, it means that the two combination valves have been connected. The only way to get it through is through the shuttle valve. Check the seal of the shuttle valve or replace the shuttle valve.

2. The combination valve works normally, and the center swivel joint can be checked in order. There are many oil channels at the central rotary joint, which are easy to cross each other.

The inspection method is: remove the A and B tubing of two walking motors, and then plug the A and B tubing of one of the hydraulic motors;

Start the engine, pull the reversing valve of the hydraulic motor that blocks the oil pipe, and check whether the oil pressure is normal (to ensure that the two valves are in good working condition);

Then observe whether the A and B oil holes of the hydraulic motors without plugging are leaking oil. If the oil and liquid pressure is abnormal and the A and B oil Wells are not blocked, the oil outlet of the center swivel joint is deemed to be poorly sealed and the oil passage has been connected with each other, and the sealing parts of the center swivel joint need to be repaired or replaced. The second and fourth oil tanks of the central rotary joint are connected with the A and B oil holes of the left walking motor, while the third and fifth oil Wells are the A and B oil holes of the right walking motor. If the second and third oil tanks are connected or the fourth and fifth oil tanks are connected, the excavator is not normally walking.

3. Hydraulic cylinder crawling.

When the piston rod of the hydraulic cylinder is extended, the main reason for the creep is that the sealing part in the hydraulic cylinder and the cylinder wall do not cooperate well, and the resistance change from static friction is large. This phenomenon is usually easy to appear when the hydraulic cylinder is newly assembled. After a period of time of use, the crawling phenomenon will naturally reduce and even disappear. If the phenomenon of hydraulic cylinder creep still exists after a period of use, the sealing parts should be checked for good condition and correct assembly.

4. The short oil inlet pipe of the combined valve ruptures.

In addition to the working pressure of the combined valve exceeding the specified value, the main reason is that the valve core of the speed limiting valve is not flexible in the valve body, and there is a phenomenon of clamping. As a result, the working oil from the shuttle valve cannot normally push the speed limiting valve, making the return oil unobstructed, resulting in the increase of the oil return resistance, causing the instantaneous pressure to rise and the pipeline rupture. This fault can be eliminated by polishing or grinding the speed limiting valve so that its core is flexible.

5. The piston rod of the power arm cylinder, bucket rod cylinder and bucket cylinder is only extended and not retracted; The return oil pressure is increased, the tubing joint is broken, and the engine load is increased.

In addition to the valve core in the normal position, the above fault is mainly caused by the shuttle valve reverse installation. From the analysis of its working principle, the former gives loop combination valve in accordance with the different working condition, attract their own work pressure oil respectively, through the shuttle valve opened the speed limiters, open the total back to the oil, make the whole hydraulic system is in normal work condition, namely each valve group and all actuators can normal oil and oil return. When leng valve installed backwards (group after the shuttle valve valve inlet slips of the tongue to a shuttle valve oil outlet, and the oil outlet after received a set of inlet valve), the total back to the speed limit on the oil valve can not get the shuttle valve drawing work pressure oil to overcome the speed limit valve spring force, unable to push the speed limit valve core to the oil return position, the speed limit at this time under the action of spring pressure in the closed valve core always back to the position of the oil.

The pressure oil output from the hydraulic pump, because there is no circuit, the pressure of each pipeline in the valve set rises abnormally, causing the pipeline rupture. If the reversing valve is pulled in this case, the hydraulic cylinder has a large volume without rod cavity, high pressure, and can barely push the piston rod into it. As the total return oil road is blocked, the valve set and tubing pressure are abnormally increased, and the diesel engine load is increased. As long as the shuttle valve is properly assembled, the above faults can be eliminated.

6. The hydraulic pump cannot realize combined flow, and the excavator cannot walk fast.

The main reason for the failure is that the spring of the back pressure valve breaks off or the spring force is too small. From the analysis of the structure and principle of the hydraulic system of the excavator, it can be seen that a backpressure valve is set at the last gate of the total return oil road of the hydraulic system, and there is 1.2MPa oil return pressure in the right return oil system.

Therefore, when the back pressure valve spring is broken and the pressure of the oil return system is reduced, the command system does not have enough pressure to push the closing valve or double speed valve, so it cannot realize the closing flow and speed up the walking speed of excavator. Replace the back pressure valve spring, so that the return oil pressure to normal value when the above fault can be eliminated.