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Analysis of the reasons for the unstable output of the hydraulic cylinder

Hydraulic cylinder is a type of hydraulic machine implementation element that converts hydraulic function into mechanical kinetic energy and performs parallel line repetitive motion (or swing output motion). It has the characteristics of simple structure, reliable work, no gap of transmission system and stable motion. It is widely used in hydraulic transmission systems of various mechanical equipment.


As a general-purpose mechanical equipment pneumatic component, the application link will inevitably be abnormal. When it is more serious, it will immediately cause the machine and equipment to not work. Therefore, its usual detection and maintenance are very critical. In general, common failures of hydraulic cylinders can be sorted out as hydraulic cylinder malfunction, fatigue promoting load, and downward movement or crawling movement of the piston rod after it is out of air.


From a practical point of view, the key parts that cause common failures of hydraulic cylinders include hydraulic cylinders, pistons, inner walls of hydraulic cylinders, guide sleeves, and tightness of piston rods and piston seals. The key positions can be sorted into four categories:


First, the piston and the piston cooperate with each other to prevent damage;


Second, the sealing of the piston rod is damaged;


Third, the damage and contusion of the mating surfaces of the piston and the guide sleeve;


Fourth, other leaks are damaged.


The consensus of the hydraulic machine manufacturing industry is that the non-action of the hydraulic cylinder should be one of the widespread common fault conditions. When this problem arises, how do people as operators diagnose and clear the root cause of common faults? ? People can start with:



1. If hydraulic oil enters the tank, check whether the hydraulic oil entering the tank has sufficient working pressure.


1. If the system software has common faults, the root cause is that there are common faults in the pump or the speed regulating valve. You should immediately check the common fault conditions of the pump or the speed regulating valve and clear it in many ways;


2. The internal leakage is serious, the piston rod and piston are loose, and the hydraulic seal is damaged. At this time, the piston rod and the piston should be tightened and the hydraulic seal should be removed immediately.


3. Due to the common failure of the pressure regulating valve, the system needs to clear the fault of the pressure valve when the working pressure is too low, and adjust the working pressure again until the required standard value can be achieved. If necessary, the pressure should be converted again, and the equipment can be debugged again if the pressure is greater;


4. The sealing ring on the piston rod is difficult to install or is severely damaged. When the inner wall hole of the hydraulic cylinder has a deep pipe groove and the nut on the piston that locks the piston rod is loose, it causes the hydraulic cylinder to return to the oil. When the cavity is severely connected or disconnected, it is impossible to operate under all normal conditions at this time. At this time, the seal ring on the piston rod and other maintenance measures should be replaced.



Second, there is oil coming in, the working pressure also meets the requirements, but the relative load is too large, which causes the hydraulic cylinder to move without moving, so it cannot be moved. This situation needs to be investigated one by one from many levels:


1. Check whether the load is too large (larger than the pre-determined value). It is very important to check whether the additional load caused by the poor installation of the hydraulic cylinder is too large. It is recommended that the hydraulic cylinder be properly installed and properly installed;


2. Check whether the connection between the hydraulic cylinder and the load is appropriate. When the interface of the load is wrong, it will cause the hydraulic cylinder cylinder body to move in a different state. At this time, the rigidity can be changed as the theme of the active bone joint. Time joint or ball joint, and the surface is preferably a spherical surface;


3. When there is a problem in the structure of the hydraulic cylinder, such as the internal bore of the piston rod and the internal bore of the cylinder liner are inseparable, the total area of the bearing capacity of the starting piston rod is insufficient, so the load cannot be promoted, or the cylinder liner of the buffer device cannot be used. The product control circuit is blocked by the piston rod, and the details are resolved separately;


4. The frictional resistance of the actuating member is large.


Solution: Troubleshoot jams and wedges in the actuator; improve the guidance and lubrication of the moving parts.


5. The working pressure of the hydraulic oil in the oil inlet is too low to reach the standard value.


Clearing method: check the leakage condition of the related oil pipe hydraulic system and solve the leakage problem; check whether the sealing ring at the piston rod and piston is damaged, embrittlement, loosening, etc .; check whether the hydraulic oil pump and pressure valve have common faults.


6. Poor hydraulic cylinder assembly line (such as poor parallelism between the piston, piston rod and cylinder head, poor flatness between the hydraulic cylinder and the operating table, too small clearance between the guide bush and the piston, etc.) causing the piston to move and hold Can't move


7. For the reasons caused by the control circuit of the hydraulic press, the key is that the hydraulic oil in the back pressure chamber of the hydraulic cylinder does not communicate with the car fuel tank, the hydraulic directional valve connected to the pump has no posture, the ball valve does not open, and the overflow valve is closed, etc. Pump oil encounters obstacles, such practical problems of visibility are solved;


8. If the dirt enters the drag position, the drag position of the hydraulic cylinder block is stuck and cannot be moved up. At this time, the position should be cleaned as soon as possible;


9. The hard chromium plated on the piston is stuck due to falling down. At this time, it must be immediately resolved to prevent the accumulation of nodules, which may become more complicated at that time.



3. In working attitude, check whether working pressure oil has entered the hydraulic cylinder. If there is no working pressure oil entering the hydraulic cylinder, the reason and check method are as follows:


1. The hydraulic reversing valve before the installation of the hydraulic cylinder was not immediately commutated, and the direct cause of the non-commutation of the hydraulic reversing valve was checked when there was no working pressure oil entering the hydraulic cylinder and was removed in many ways;


2. The hydraulic station device is not supplying oil. Check whether the hydraulic station system and other hydraulic solenoid valves and other accessories are faulty.


3Why doesn't the hydraulic cylinder act? Hydraulic oil does not enter the hydraulic cylinder. Solution: Check whether the oil pipeline, hydraulic cylinder circuit, and hose joint have been blocked. Check the related circuit oil pipes from the hydraulic cylinder to the hydraulic station and solve the blockage; check the gap between the cone valve of the speed control valve and the high-pressure gate valve. Is the tightness good? Check if the solenoid valve is yellow or the solenoid coil is burnt, and the oil pipe is not switching properly.


4. The lateral load of the piston is too large, it is very hard or pulls the cylinder and bites.


Clearing method: When installing a hydraulic cylinder, make sure that the centerline of the cylinder is consistent with the operating orientation, so that the load on the hydraulic cylinder is based on the centerline of the cylinder as much as possible to prevent the situation of axial force. When the long hydraulic oil cylinder rotates horizontally, the piston causes rigidity due to weight, causing the guide sleeve and piston rod to eccentrically load, resulting in damage to the seal of the cylinder head and oil leakage.


The following countermeasures can be adopted: plan to increase the piston rod and adjust the inner hole of the piston rod to be produced and processed into a convex shape, so that the piston rod can self-position, improve the pressure situation, and reduce and prevent the cylinder; the ball rod is connected to the piston by ball head. 6. The back pressure of the hydraulic cylinder is very large.


Clearing method: Reduce back pressure. The key reason why the hydraulic cylinder cannot be positioned is that the working pressure of the hydraulic oil in the oil inlet is too low, that is, the pressure is not enough. The pressure of the hydraulic transmission system is not enough. The key is the common failure of the hydraulic oil pump, the drive motor and the pressure reducing valve. Other reasons include: blocked oil filter, too small nominal diameter of the fuel pipe, too high or too low hydraulic oil viscosity; Into too much gas; serious environmental pollution; incorrectly inserted pipes; damaged barometer, etc.



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