Reasons for the slow lifting of the long reach boom of the excavator

There are many reasons for the slow lifting of the long reach boom of the excavator. This article gives a detailed analysis and diagnosis of this fault, so that we can reduce the occurrence of faults as much as possible during the construction and make our construction work smoothly.

Describe the slow or weak lifting of the long reach boom of the excavator from the following three points. For example, the reduction of the output power of the oil cylinder will cause the boom to lift slowly, and the decrease of the pressure difference between the two sides of the piston will also cause the boom to lift slowly. The decrease in the output flow of the oil pump will inevitably cause the boom to rise slowly! The details are as follows:

1. Failure phenomenon

Analysis: When the excavator is working, it will be found that the long reach boom lifts slowly.

2. Reason analysis

Excavator long reach boom is lifted by the pressure oil output by the oil pump through the pipeline through the valve into the rear cavity of the extension boom boom cylinder. The piston in the cylinder moves under the action of the working oil pressure, and the boom is moved by the piston rod. lift.

From this point of view, the lifting speed of the long reach boom is related to the pressure and flow of the oil entering the cylinder. According to the reason that the power of the input oil cylinder is equal to the output power of the oil cylinder, and then according to the power P of the input hydraulic oil cylinder equal to the product of the working pressure of the hydraulic oil cylinder and the flow rate of the hydraulic oil cylinder, the slow lifting of the boom of the excavator is mostly due to the input hydraulic pressure. The power of the cylinder is reduced, that is, the power input to the cylinder is reduced. The reasons that cause the power of the input cylinder to decrease are:

1. The influence of the oil pump is proportional to the movement speed of the piston in the oil cylinder and the working flow of the oil entering the oil cylinder. If the output flow of the hydraulic oil pump is reduced, the boom cylinder will inevitably be lifted slowly. Further analysis, the actual flow of the oil pump is equal to the product of the theoretical flow of the oil pump and the total efficiency (the sum of the volumetric efficiency of the oil pump and the mechanical efficiency). If the total efficiency of the oil pump decreases, the actual flow of the oil pump must also decrease. The main reasons for the decrease of the total efficiency of the oil pump are: the increase of the leakage of the oil pump and the increase of the mechanical friction loss.

2. The influence of the oil cylinder The piston sealing ring of the hydraulic oil cylinder is damaged, the oil cylinder is strained, and the oil cylinder cover sealing ring is damaged. The power is reduced, which is manifested by the slow lifting speed of the boom.

3. The effect of oil circuit leakage. The suction section (oil pump to tank) of the oil pump is not well sealed and sucks in air, which affects the pump oil efficiency; the pressure section from the oil pump to the cylinder leaks oil to the outside of the system or leaks back to the tank through the control valve. Both will reduce the flow of oil into the cylinder and reduce the pressure, resulting in slow boom lift.

4. The influence of the oil circuit blockage. The working oil of the hydraulic system generally has mechanical impurities. These impurities block the small part of the oil circuit in the oil circuit, which reduces the flow of oil into the cylinder and also causes the pressure to drop. Therefore, the output power of the oil cylinder is reduced and the long reach boom lift is slow.

The filter screen at the oil suction port is blocked, which will increase the vacuum of the oil suction section of the oil pump. When the air pressure in the separated oil is reached, the air dissolved in the oil is separated and sucked by the oil pump, which affects the output power of the oil pump. According to the output power of the oil cylinder equal to the input oil cylinder power of the oil pump, the boom lift of the excavator is slow due to the decrease of the power of the oil cylinder.

The blockage of the oil filter or the radiator in the oil return path will increase the back pressure of the oil cylinder, resulting in a small pressure difference between the two sides of the oil cylinder piston. According to the piston moving speed of the oil cylinder and the pressure on both sides of the piston, there is a proportional relationship. When the pressure difference between the two sides of the piston decreases, the boom of the excavator rises slowly.

5. The effect of the valve. If the setting pressure of the safety valve (overload valve or overflow valve) is too low or the valve is not closed tightly, it will cause the pressure of the working fluid in the system to drop. The pressure is also reduced, so the cylinder lifts slowly due to the low pressure.

The check valve is not tightly closed due to mechanical impurities, or the valve and valve seat are not tightly sealed. The result is the same as the above situation.

The gap between the valve core of the reversing valve and the mating pair is too large, causing part of the pressure oil to flow back to the tank during operation, and the result is the same as the above situation.

6. The inlet and outlet oil pipe joints of the oil pump are connected reversely, and the oil cylinder does not move.