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Qianglin hydraulics

Fault diagnosis and treatment of hydraulic cylinder

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1, wrong action or action failure
The reasons and methods of treatment are as follows:
(1) The valve core is stuck or the valve hole is blocked. When the flow valve or direction valve core is stuck or the valve hole is blocked, the hydraulic cylinder is prone to accidental action or action failure. The pollution of the oil should be checked at this time; Check whether the dirt or colloidal sediment is stuck in the valve core or plug the valve hole; Check valve body wear, clean and replace system filters, clean fuel tank, replace hydraulic media.
(2) The piston rod and cylinder are stuck or the hydraulic cylinder is blocked. At this time, no matter how manipulated, the hydraulic cylinder does not move or have little action. At this time, it should be checked whether the piston and piston rod seals are too tight, whether they enter the dirt and colloidal deposits: whether the axles of the piston rod and cylinder are aligned, whether the fragile parts and seals fail, and whether the load is too large.
(3) The control pressure of the hydraulic system is too low. The throttle resistance in the control line may be too large, the flow valve is not adjusted properly, the control pressure is not appropriate, and the pressure source is disturbed. The control pressure source should be checked at this time to ensure that the pressure is adjusted to the specified value of the system.
(4) Air enters the hydraulic system. Mainly because of leaks in the system. At this point should check the hydraulic tank level, hydraulic pump suction side seal and pipe joint, oil suction crude filter is too dirty. If so, the hydraulic fluid should be added, the seal and pipe joint should be handled, and the coarse-filter core should be cleaned or replaced.
(5) The initial movement of the hydraulic cylinder is slow. In the case of low temperature, the hydraulic fluid viscosity is large and the fluidity is poor, causing the hydraulic cylinder to move slowly. The improvement method is to replace the hydraulic oil with better viscous temperature performance. At low temperatures, the oil temperature can be raised by heaters or by heating the machine itself to increase the oil temperature at startup. The normal working oil temperature of the system should be maintained at about 40 °C.
2, can not drive the load when working
The main manifestations are the inaccurate stop of the piston rod, insufficient thrust, declining speed, and unstable work. The reasons are:
(1) Internal leakage of hydraulic cylinder. The internal leakage of the hydraulic cylinder includes the leakage caused by excessive wear of the hydraulic cylinder body seal, piston rod and seal cover seal, and piston seal.
The piston rod and seal cover seal leakage is due to the seal crease, squeeze, tear, wear, aging, deterioration, deformation, etc., at this time should be replaced with a new seal.
The main cause of excessive wear of piston seals is improper adjustment of speed control valve, resulting in excessive back pressure and improper installation of seals or hydraulic oil pollution. The second is that foreign matter enters during assembly and the quality of sealed materials is not good. The consequence is that the movement is slow and weak. In serious cases, it will also cause damage to the piston and cylinder, and there will be a "pull cylinder" phenomenon. The method of handling is to adjust the speed control valve and compare the installation instructions to do the necessary operation and improvement.
(2) Hydraulic loop leakage. Including leakage of valves and hydraulic lines. The maintenance method is to check and eliminate the leakage of the hydraulic connection pipe by manipulating the reversing valve.
(3) Hydraulic oil passes through the overflow valve to return to the fuel tank. If the overflow valve enters the dirt and sticks the valve core, the overflow valve is often opened. The hydraulic oil will flow directly back to the fuel tank through the overflow valve, causing the hydraulic cylinder to enter without oil. If the load is too large, although the adjustment pressure of the overflow Valve has reached the maximum rating, the hydraulic cylinder still does not receive the thrust required for continuous action and does not move. If the adjustment pressure is low, it is not enough to carry the required vertebral force because the pressure is not enough, which is manifested as insufficient thrust. Check and adjust the overflow valve at this point.
3, piston sliding or crawling
The hydraulic cylinder piston slip or crawling will make the hydraulic cylinder unstable. The main reasons are as follows:
(1) Hydraulic cylinder internal astringent. The internal parts of the hydraulic cylinder are improperly assembled, the parts are deformed, worn, or the tolerance of the shape is excessive, and the action resistance is too large, so that the piston speed of the hydraulic cylinder changes with the position of the stroke, and sliding or crawling occurs. Most of the reasons are due to the poor assembly quality of parts, scars or sintered iron chips on the surface, which increases the resistance and decreases the speed. For example, the piston is not centered with the piston rod or the piston rod is bent, the hydraulic cylinder or piston rod is offset to the guide rail installation position, and the sealing ring is too tight or loose. The solution is to repair or adjust, replace damaged parts and remove iron chips.
(2) Poor lubrication or extremely poor hydraulic cylinder aperture processing. Because the piston and the cylinder, the guide rail and the piston rod have relative motion, if the lubrication is poor or the hydraulic cylinder aperture is too poor, it will exacerbate the wear and reduce the linear line in the center of the cylinder. In this way, when the piston is working in a hydraulic cylinder, the friction resistance will be large and small, resulting in slippage or crawling. The elimination method is to repair the hydraulic cylinder first, then prepare the piston according to the requirements, repair the piston rod, and configure the guide sleeve.
(3) Hydraulic pumps or hydraulic cylinders enter the air. Air compression or expansion can cause the piston to slip or crawl. The exclusion measure is to check the hydraulic pump, set up a special exhaust device, and quickly operate the entire trip to and from exhaust several times.
(4) The quality of the seal is directly related to sliding or crawling. When the O-shaped sealing ring is used under low pressure, compared with the U-shaped sealing ring, due to the high surface pressure and the large difference in dynamic and dynamic friction resistance, sliding or crawling is easy to occur; The surface pressure of the U-type sealing ring increases with the increase of the pressure. Although the sealing effect also increases accordingly, the difference of the dynamic and static friction resistance also becomes larger, and the internal pressure increases, affecting the rubber elasticity. Due to the increased contact resistance of the lip edge, The sealing ring will be overturned and the lip edge will be elongated. It will also easily cause slippage or crawling. To prevent it from tipping, the supporting ring can be used to maintain its stability.