Composition of excavator boom lifting slow for a variety of reasons, I give you a detailed analysis and diagnosis of this fault, so that we can minimize the occurrence of accidents in the construction, and make our construction can be carried out smoothly. Excavator boom lifting slow or powerless mainly due to the following three reasons: cylinder output power will reduce the boom lifting slow, the pressure difference between the two sides of the piston will also lead to slow lifting of the boom, the hydraulic pump output flow reduction will inevitably lead to slow lifting of the boom! Detailed reasons are as follows:
1. Failure Phenomenon
When the excavator is working, you will find the big arm lifting slowly.
2. Cause analysis
Excavator boom lift, is by the oil pump output pressure oil down the pipe through the value into the back cavity of the boom cylinder, the piston in the cylinder under the action of the pressure of the working fluid to move, through the piston rod will be lifted up the big arm.
It appears that the the speed at which the boom lifts is related to the pressure and flow of the fluid entering the cylinder. According to the power of the input cylinder is equal to the power of the cylinder output this reason,according to the power of the input hydraulic cylinder and the product of the flow into the hydraulic cylinder, then the excavator boom lifting slowly is mostly due to the power of the input cylinder is reduced due to the reduction of the power of the input cylinder. Causes of the reduction of the power of the input cylinder are:
1. Impact of oil pumps
According to the piston in the cylinder moving speed and the working flow into the cylinder oil is proportional to the relationship, if the hydraulic oil pump output flow is reduced, will inevitably make the big arm cylinder lifting slowly. Further analysis, the actual flow rate of the oil pump is equal to the theoretical flow rate of the oil pump and the product of the total efficiency (the sum of the volumetric efficiency of the oil pump and mechanical efficiency). If the total efficiency of the oil pump decreases, the actual flow of the oil pump is bound to decrease. So that the total efficiency of the oil pump is reduced mainly due to: oil pump leakage increases and mechanical friction loss increases.
2. Impact of the cylinder
Hydraulic cylinder piston seal damage, cylinder strain, cylinder seal damage caused by oil tampering cavity or oil leakage, so that the volumetric efficiency in the cylinder is reduced, that is, the cylinder itself is less efficient, so the output power is reduced, which is manifested in the slow lifting speed of the power arm.
3. Effects of oil line leaks
The suction section of the oil pump(oil pump to the tank) pipeline closed and poor air intake, affecting the pumping efficiency, the oil pump to the cylinder pressure range to the outside of the system leakage or through the manipulation of the valve leakage back to the tank, will make the oil flow into the cylinder is reduced, the pressure is reduced, resulting in the slow lifting of the movable arm.
4. Effects of clogged oil lines
The working fluid of the hydraulic system will generally have mechanical impurities, these impurities in the oil circuit in the flow of oil carrying surface of the small parts of the blockage, so that the flow into the cylinder fluid flow is reduced, but also cause pressure reduction. As a result, the output power of the cylinder decreases and the boom lifts slowly.
Suction port at the screen clogging will make the oil pump suction section of the vacuum increases, when reaching the separation of air pressure in the oil, the air dissolved in the oil is separated from the oil pump suction and affect the output power of the pump. According to the output power of the oil cylinder is equal to the input cylinder power of the oil pump, so the power of the oil cylinder decreases and the excavator boom lifting slowly.
A clogged oil filter or radiator in the return line section will increase the back pressure of the cylinder, resulting in a decrease in the pressure difference between the two sides of the cylinder piston. According to the positive relationship between the piston movement speed of the cylinder and the pressure on both sides of the piston, when the pressure difference between the two sides of the piston decreases,the excavator will lift the boom slowly.
5. Import of valves
Safety valve(overload valve or relief valve) regulating pressure is too low or the valve is not closed tightly, will cause the system working fluid pressure drop, according to Bacchus pressure everywhere equal theorem, so the pressure in the cylinder is also reduced, so the cylinder due to low pressure and lifting speed is slow.
Check valve due to mechanical impurities so that the valve and the valve seat is not closed tightly, or the valve and the valve seat sealing bad and closed tightly, the result is the same as the above situation. The clearance between the spool of the directional valve and the mating partner is too large, resulting in part of the pressure oil will flow back to the tank when working, the result is the same as the above.
3. Diagnosis and troubleshooting
If the action of the hydraulic working device are slow, it indicates that the fault of the slow lifting of the boom cylinder is in the main oil supply or the total return part. If other working devices work at a normal speed, only the boom cylinder lifting slow, it shows that the lifting powerless fault in the arm.
1. Appearance check the main oil circuit leakage, if the main oil circuit has leaked out of the system outside the oil trace, indicating that the big arm lifting powerless where the fault lies, should be along the oil trace to find out the cause of the leakage, and to be ruled out.
2. Check the oil liquid in the mailbox, if the oil liquid is seriously insufficient or too many bubbles, it is due to the main oil circuit pressure caused by the slow lifting of the big arm, it should be refilled with oil, so that the liquid level to meet the height requirements. If there are too many air bubbles, it may be that the oil circuit and air circuit at the rotary joint are connected, and the rotary joint seal should be replaced. If the oxidized oil is black-brown and emits a foul odor, the oil is deteriorated and should be replaced.
3. Check the oil temperature, if the system oil temperature exceeds 80℃， indicating that it is the cause of the slow lifting of the arm. Should be given to cooling, if the fault disappears after cooling, provide that the radiator heat dissipation is poor or overload continuous work time is too long. In addition, if the oil temperature is low when the work is normal, the oil temperature is low when the work is normal, the oil temperature is high when the big arm lifting speed is slow, indicating that the oil quality is bad of the system hydraulic component wear, is to make the system efficiency is reduced. The former mostly occurs in the use of the period, the latter mostly occurs in the period of wear and tear.
4. Check the main safety valve, if the safety valve adjustment stud screwed (each screwed into a pressure change of 2.352MPa) pressure rose to the prescribed value , and the arm lifting speed is normal, it is the main safety valve is improperly adjusted.
If the adjustment is ineffective, indicating that the main safety spool stagnation in the open position or closed poorly due to, should be removed and checked and be excluded. If the adjustment spring is broken, it should be replaced.
5. In the adjustment of the main safety valve, pressure regulating stud each screwed into a circle but the pressure does not increase (2.352MPa) , indicating that the oil is faulty. If the excavator boom lifting slow failure occurs in the early (go together period), proving that the suction channel has a leak, if it occurs in the depletion period, proving that the oil pump wear and tear is serious and pumping efficiency due to low, should be repaired or replaced.
6. Check the cylinder, if the cylinder is lifted after the control valve is in the middle position, the arm has a significant automatic decline, it may be poor cylinder sealing, cylinder safety valve is not closed tightly, oil pipe leakage control valve oil leakage, should be further to find out the reasons for and exclude the symptoms.
If the cylinder lift occurs slowly in the early days, most of the assembly of the cylinder seal damage the possibility of a large number of assembly in the assembly did not remove the manufacturing of mechanical impurities (metal shavings, sand, etc.) will be the safety valve spool or check valve is stuck in the open position affecting the spool of the valve closed, pipeline joints connected to the loose seals are damaged and leakage of oil. All of the above reasons can cause a drop in pressure in the hydraulic system, resulting in the excavator boom lift slowly, and should be further identified and excluded.
If the boom cylinder safety valve regulating pressure is lower than the specified value , should be adjusted. The method is: the screw plug screwed out in the spring to increase the pad for boosting (gasket per 1mm thicker, can increase the pressure 2.45MPa).
Post time: Apr-28-2024