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Up posture! The reason why the excavator's boom is lifted slowly
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Up posture! The reason why the excavator's boom is lifted slowly Time: 2015-05-28 Source: http://
There are many reasons for the slow lifting of the excavator boom. This article gives detailed analysis and diagnosis for this fault, so that we can reduce the occurrence of faults as much as possible in the construction and make our construction go smoothly.
     Describe the slow or weak lift of the excavator boom from the following three points. For example, if the output power of the cylinder is reduced, the boom will be lifted slowly. The pressure difference between the two sides of the piston will also cause the boom to lift slowly. The hydraulic pump output will be slow. The reduction in flow will inevitably cause the boom to lift slowly! The details are as follows:
1, the fault is like
Analysis: When the excavator is working, it will find that the boom is lifted slowly.
2, the cause analysis
     The excavator boom is lifted by the pressure of the oil pump. The oil enters the rear cavity of the boom cylinder through the valve. The piston in the cylinder moves under the action of the working oil pressure, and the boom is lifted by the piston rod. From this point of view, the speed at which the boom is lifted is related to the pressure and flow into the cylinder fluid. According to the principle that the power of the input cylinder is equal to the output power of the cylinder, and then the power P of the input hydraulic cylinder is equal to the product of the working pressure of the hydraulic cylinder and the flow rate of the hydraulic cylinder, then the boom lift of the excavator is mostly due to the input hydraulic pressure. The power of the cylinder is reduced, that is, the power of the input cylinder is reduced. The reasons for the reduction in the power of the input cylinder are:
(1) The influence of the oil pump is proportional to the working speed of the piston in the cylinder and the working flow rate of the oil entering the cylinder. If the flow rate of the hydraulic pump is reduced, the boom cylinder will be lifted slowly. Furthermore, it is analyzed that the actual flow rate of the oil pump is equal to the product of the theoretical flow rate 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 is reduced, the actual flow rate of the oil pump is also necessarily reduced. The main reason for reducing the overall efficiency of the oil pump is that the oil pump leakage increases and the mechanical friction loss increases.
(2) The influence of the cylinder The hydraulic cylinder piston seal ring is damaged, the cylinder is pulled, the cylinder head seal ring is damaged, and the oil cavity or oil leakage is caused, so that the volumetric efficiency in the cylinder is reduced, that is, the efficiency of the cylinder itself is reduced, so the output The power is reduced, which is manifested by the slow lifting speed of the boom.
(3) Influence of oil passage leakage The suction section of the oil pump (oil pump to tank) is poorly sealed and sucks in air, which affects the pump oil efficiency; the oil pump to the cylinder's pressure section leaks oil to the outside of the system or leaks back to the tank through the control valve. Both will reduce the flow rate of oil entering the cylinder and reduce the pressure, resulting in slow boom lift.
(4) Influence of oil blockage The hydraulic fluid of the hydraulic system generally has mechanical impurities. These impurities are blocked in the small oil-bearing surface of the oil passage, which reduces the flow rate of the oil entering the cylinder and also causes pressure. reduce. As a result, the cylinder output power is reduced and the boom is lifted slowly.
     Blockage of the filter at the suction port will increase the vacuum of the oil suction section of the oil pump. When the air pressure in the separation oil is reached, the air dissolved in the oil is separated and sucked by the oil pump to affect the output of the oil pump. . According to the output power of the cylinder is equal to the input power of the oil pump, the excavator boom is lifted slowly due to the reduction of the power of the cylinder.
     The oil filter net or the radiator of the return oil passage is blocked, which will increase the back pressure of the oil cylinder, resulting in a small pressure difference between the two sides of the cylinder piston. According to the piston moving speed of the 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 is reduced, the excavator boom is lifted slowly.
(5) Influence of valve The safety valve (overload valve or relief valve) is too low in setting pressure or the valve is not closed tightly, which will cause      The working oil pressure in the system drops. According to the equal theorem of the Basque pressure, the pressure in the cylinder is also reduced, so the cylinder is slow to lift due to low pressure.
     The check valve is not tightly closed due to mechanical impurities, or the valve and the valve seat are poorly sealed, and the result is the same as above.
     The clearance between the spool and the mating pair of the reversing valve is too large, so that some of the pressure oil will flow back to the tank during operation, and the result is the same as above.
(6) The inlet and outlet oil pipe joints of the oil pump are reversed, and the cylinder does not operate.
Excavator boom lift slow failure analysis
3. Diagnosis and elimination
     If the hydraulic working device moves slowly, it indicates that the booming cylinder has a slow lifting failure in the main oil supply or total oil return portion. If the working speed of other working devices is normal, only the boom cylinder is lifted slowly, indicating that the lifting failure is in the arm branch.
(1) Appearance inspection Leakage outside the main oil circuit If the main oil circuit leaks oil traces outside the system, it indicates that the fault of the boom lifting is weak. The cause of the oil leakage should be identified along the oil track and excluded.
(2) Check the oil liquid in the fuel tank. If the oil is seriously insufficient or the air bubbles are too much, the boom lift is slow due to insufficient pressure of the main oil passage. The oil should be filled to make the liquid level meet the height requirement. If there are too many air bubbles, the oil circuit at the rotary joint may be connected to the gas path, and the rotary joint seal ring should be replaced. If the oil oxidizes and deteriorates in a dark brown color and emits an odor, it indicates that the oil has deteriorated and should be replaced.
(3) Checking the oil temperature If the oil temperature of the system exceeds 80 °C, it indicates that the cause of the boom lift is slow and should be cooled. If the fault disappears after cooling, it proves that the heat sink has poor heat dissipation or the heavy load has been working continuously for too long.
     In addition, if the oil temperature is low, the work is normal, and when the oil temperature is high, the boom lifting speed is slow, indicating that the oil quality is deteriorated or the hydraulic components of the system are worn out, so that the system efficiency is lowered. The former occurs mostly during the period of use. The latter mostly occurs during the wear and tear period.
(4) If the main safety valve is inspected, if the adjustment stud of the safety valve is screwed in (the pressure change is 2.352 MPa per rotation), the pressure rises to the specified value, and the lifting speed of the boom is normal, which is caused by improper adjustment of the main safety. .
     If the adjustment is invalid, it indicates that the valve plug of the main safety valve is stuck in the open position or the closing is not strict, it should be removed and inspected and excluded. If the pressure regulating spring is broken, it should be replaced.
(5) When adjusting the main safety valve, the pressure regulating stud is screwed in one turn but the pressure does not increase (23.52MPa), indicating that the oil pump is faulty. If the slow lifting of the excavator boom occurs in the early stage (the running-in period), it proves that there is air leakage in the oil suction passage; if it occurs in the wear period, it proves that the oil pump is seriously worn and the pumping efficiency is low, it should be repaired or replaced.
(6) Checking the cylinder If the control valve is in the neutral position after the cylinder is lifted, the boom will obviously drop automatically. It may be that the cylinder is poorly sealed, the cylinder safety valve is not closed tightly, and the oil leakage control valve leaks oil. Identify the cause and rule out the disease.
     If the cylinder lift slowly occurs in the early stage, most of the seals are likely to be damaged when assembling the cylinder; it is also possible to remove the mechanical impurities (metal scraps, sand, etc.) from the safety valve spool or one-way during assembly. The valve card affects the closing of the spool in the open position; the looseness of the pipe joint is damaged and the oil leaks. All of the above reasons can cause the pressure in the hydraulic system to drop, causing the excavator's boom to lift slowly, and then identify the cause and eliminate it.
     If the safety valve setting pressure of the boom cylinder is lower than the specified value, it should be adjusted. The method is as follows: the screw plug is screwed out, and the pad is raised to the pressure in the spring (the thickness of the gasket is increased by 1 mm, and the pressure can be increased by 2.45 MPa).