Created on:2021-09-16 10:26

Construction machinery_ Excavator hydraulic pump failure_ Typical fault analysis

Construction machinery_ Excavator hydraulic pump failure_ Typical fault analysis

① Fault I

Fault phenomenon: the excavator rotates slowly and walks on the left, while the right walking and bucket movement speed are normal, the speed change of boom and jib is not obvious, and the engine is normal.

Test results: the working pressure of the auxiliary pump is within the normal range; When the multi-way directional valve is in the middle position, the output pressure of the front and rear pumps is normal; In the operation state, the front and rear pumps can reach the set pressure after loading; Support the left track so that when the left travel motor is in no-load, the speed of the drive wheel is very low, which is basically the same as that in heavy load.

Fault analysis: in the excavator hydraulic system, the swing and left travel motors are supplied by the front pump, the right travel and bucket actions are completed by the rear pump alone, and the boom and jib hydraulic cylinders can realize the combined operation of two pumps. Therefore, it is first determined that the front pump works normally. In the non operation state (the multi-way directional valve is in the middle position), the pressure of the front and rear pumps and the oil supply pressure of the auxiliary pump are normal, indicating that the unloading of the pump can be realized during flow control, that is, the differential cylinder of the control variable has pushed the swashplate to minimize its inclination, and the piston of the differential cylinder is at the rightmost end, which is consistent with the control principle. When only the left travel handle is operated, the inclination angle of the front pump swashplate shall be adjusted to the maximum immediately to realize the power adjustment of light load high speed and heavy load low speed. The speed test results show that the front pump does not complete the control of increasing displacement in flow control, the pump is always in a small displacement state, the hydraulic power is less than the engine output power, the engine speed and sound are normal, and the pump does not need power regulation. After loading, the pressure can reach the set value, and the speed of the actuator does not change significantly with light load, which can prove that the possibility of slow speed caused by leakage in the pump is very small. Therefore, it is determined that the flow control piston or differential cylinder piston is stuck.

Treatment: according to the inspection principle from easy to difficult, first remove the flow control piston in the regulator. It is found that the flow control piston moves freely without clamping, so this is not the fault point; Check the differential cylinder piston again and find that the piston is stuck, which proves that the fault is caused by the piston being stuck. After removing the differential cylinder piston for cleaning and other treatment, apply clean hydraulic oil for assembly. After checking that the piston can move freely, assemble the regulator according to the regulations, and then start the engine for test run, and the fault phenomenon disappears.

② Fault II

Fault phenomenon: the work is basically normal under light load (such as excavator rotation), and the engine is overloaded or even stalled under heavy load (such as operating boom or compound action).

Test results: the oil supply, air intake and power output of the engine are basically normal, and the working pressure of the auxiliary pump is within the normal range; When the multi-way directional valve is in the middle position, the output pressure of the front pump is normal, and the output pressure of the rear pump is higher than the normal value.

Fault analysis and treatment: according to the control principle of the excavator hydraulic pump, the absorbed power of the hydraulic pump should be close to the output power of the engine during normal operation of the excavator. Therefore, the pump should adjust its displacement in time according to the load, otherwise the engine will be overloaded. Combined with the test results, the pressure of the rear pump in the middle position of the control valve exceeds the normal value, and this pressure is generated by the hydraulic oil output by the rear pump through the back pressure valve. There are two reasons for this phenomenon: first, the back pressure valve itself, but from the perspective of system composition, the back pressure valve consists of a throttle valve and a parallel valve. Normally, the oil will generate back pressure through the throttle valve. After the throttle valve is blocked, the overflow valve will open to generate back pressure. From the perspective of probability, the two valves are less likely to fail at the same time; Second, the output flow of the rear pump is too large. Through analysis, it is concluded that the output flow of the rear pump is too large. When the excavator encounters a large load, the flow still cannot be reduced through the regulator, resulting in engine overload. Therefore, it is determined that the differential cylinder piston controlling the displacement of the rear pump is stuck at the left end. Through disassembly, inspection and treatment (the same as fault I), the excavator returned to normal.

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