Common Causes and Troubleshooting of Hydraulic System Malfunctions

Common causes and troubleshooting of hydraulic system faults/Here is a brief analysis of the three common types of hydraulic system faults: hydraulic oil temperature rise, hydraulic system leakage, hydraulic system vibration and noise.
1. Hydraulic system oil temperature is too high
Excessive oil temperature in hydraulic systems can lead to a series of serious consequences:

1) Due to high oil temperature, the viscosity of the oil decreases, leading to increased leakage and a decrease in volumetric efficiency, even affecting the normal movement of the working mechanism.

2) Excessive oil temperature can also cause the oil to deteriorate, produce oxidizing substances, block small holes or gaps in hydraulic components, and prevent the components from working properly.

3) Excessive oil temperature may cause thermal deformation of machine tools or machinery, damaging their original accuracy.

Reasons for high oil temperature in hydraulic system

1) Poor heat dissipation. When designing and selecting, if the fuel tank is too small, it may cause the oil to circulate too quickly, or if a cooler is used due to high ambient temperatures but the cooling effect is poor. These are all reasons for poor heat dissipation.

2) System uninstallation circuit malfunction. Usually, an unloading valve is installed at the pump outlet of the system. When the system is not loaded and does not require pressure oil, the system unloads to reduce energy loss. If the unloading valve fails to operate properly and the oil still overflows from the relief valve back to the oil tank when no pressure oil is needed, it will cause the oil temperature to rise.

3) The impact during commutation and speed switching.

4) Serious leakage. Most people believe that it has nothing to do with temperature rise. As we all know, leaks can cause energy loss. So what is the conversion of this energy loss into? In fact, they are all converted into heat energy, which causes the oil temperature to rise.

5) Air or moisture enters the oil. When a hydraulic pump converts oil into pressure oil, the presence of air and moisture can increase heat and cause overheating.

6) Misuse of hydraulic oil with too high viscosity or hydraulic oil becoming larger. Oxidation of hydraulic oil or low ambient temperature can increase viscosity, and hydraulic oil with too high viscosity will increase friction and cause heat generation.
solution
1) Design a fuel tank of sufficient size and install a cooler if necessary. If the ambient temperature is too high, isolate the system from the outside world. Strictly control the system temperature within the range of 20-60 ℃, with a maximum not exceeding 70 ℃.
2) When high-pressure oil unnecessarily overflows from the overflow valve back into the oil tank for a long time, the design should be improved by using a variable displacement pump or the correct unloading method.
3) Try to shorten the pipeline as much as possible, avoid being too thin or bent, and strive to ensure smooth oil flow.
4) The areas where hydraulic pumps and their connections are prone to leakage should be sealed and the connecting parts should be tightened to prevent volume loss and heat generation.
5) When the setting value of the pressure regulating valve is too high, it is best to reduce the working pressure to minimize unnecessary energy loss.
6) Choose hydraulic oil with appropriate viscosity.
2. Vibration and noise of hydraulic system
Hydraulic shock, unbalanced force during rotation, and changes in frictional resistance are all the root causes of different forms of vibration. In hydraulic equipment, noise is often generated after vibration. In practical use, the phenomenon of vibration and noise in hydraulic pumps and valves often occurs, mainly due to four reasons.
Reasons for Vibration and Noise in Hydraulic Systems
1) Hydraulic pump suction
a. Air intrusion is the main cause of vibration and noise in hydraulic systems. Because air entering the hydraulic system can cause cavitation. Cavitation phenomenon refers to the sudden explosion of bubbles.
b. The hydraulic pump cannot suck up oil. The hydraulic system's oil level is too low, the suction port is too high, the oil filter area is too small, the hydraulic oil viscosity is too high, and the oil tank is not permeable to air, all of which cause the hydraulic pump to be unable to suction oil, resulting in noise.
2) The hydraulic pump was damaged during use.
In use, due to wear and tear of hydraulic pump components (blades, oil distribution plate), excessive clearance, insufficient flow, high speed, pressure fluctuations, noise can also be generated.
3) The overflow valve is malfunctioning.
Overflow valve is a pressure regulating valve, and its instability causes pressure fluctuations, resulting in vibration and noise. The pollutants in hydraulic oil cause blockage of the damping holes, causing the oil to pass through and block at times; The spring of the overflow valve is deformed and the valve core is stuck; It will cause pressure fluctuations in the overflow valve.
4) Mechanical vibration.
The most common mechanical vibrations in hydraulic systems are pipeline shaking and vibrations caused by unbalanced rotating parts of electric motors and hydraulic pumps.
solution
1) To address the issue of air pockets, an exhaust device is often installed on the hydraulic cylinder. Additionally, after driving, the actuator is rapidly cycled back and forth several times to exhaust the air.
2) To address the issue of hydraulic pumps not being able to suck up oil, it is necessary to strengthen the sealing of the oil inlet; The height from the oil suction port to the pump suction port should be less than 500mm, and hydraulic oil with appropriate viscosity should be selected.
3) The phenomenon of damage to hydraulic pumps during use should strengthen the maintenance and upkeep of hydraulic pumps.
4) Attention should be paid to the cleaning and inspection of the overflow valve. If any damage is found, it should be repaired or replaced in a timely manner.
5) In response to the phenomenon of mechanical vibration, when the oil pipe is slender and has many bends, a fixed pipe clamp should be added to adjust the installation accuracy of the motor and hydraulic pump, which should not be less than 0.1mm.
3. Hydraulic system leakage
Hydraulic system leakage is divided into external leakage and internal leakage. The causes of leakage are complex and mainly related to vibration, temperature rise, pressure difference, clearance, and improper design, manufacturing, installation, and maintenance. Compared to other types of faults, hydraulic system leakage is more intuitive. Through visual inspection, it can be seen that leakage causes oil loss, environmental pollution, and equipment wear. The main reasons for leakage are seal damage and aging, excessive oil filling leading to high liquid level, high oil temperature, component damage, and large fitting clearance.
Reasons for hydraulic system leakage
1) Due to poor lubrication between the motion pairs, improper material selection, and poor precision in processing, assembly, and installation, early wear can occur, resulting in increased clearance and leakage;
2) Seals are widely used in hydraulic components for sealing. If the sealing material is poor, the physical and chemical properties are unstable, the mechanical strength is low, and the elasticity and wear resistance are low, they will all leak due to poor sealing effect;
3) Unreasonable groove size design for installing seals can also cause leaks;
4) The surface roughness value of the joint surface is large, the flatness is poor, deformation after compression and uneven fastening force cause leakage;
5) Leakage caused by component oil leakage and poor oil return pipeline;
6) Excessive oil temperature, decrease in oil viscosity, or use of oil with too low viscosity causing leakage;
7) The system pressure is set too high, causing leakage due to insufficient pre compression of the sealing components;
8) Defects in the casing of hydraulic component castings can also cause increased leakage.
solution
1) The machining accuracy and fitting clearance of the motion pair using gap sealing should be strictly controlled; Improving the sealing device, such as replacing the "V" - shaped seal at the piston rod with a "Yx" - shaped seal ring, not only reduces friction but also ensures reliable sealing.
2) Try to minimize the number of oil pipe joints and flanges.
3) Installing the hydraulic valve station in the hydraulic system closer to the actuator can greatly reduce the total length of the hydraulic pipeline and the number of pipe joints.
4) Hydraulic shock and mechanical vibration directly or indirectly cause loosening of system pipeline joints, resulting in leakage.
5) The amount of leakage is inversely proportional to the viscosity of the oil. If the viscosity is small, the amount of leakage will be large. Therefore, hydraulic oil should be replaced in a timely manner according to different temperatures to reduce leakage.
6) Control temperature rise.