1. Characteristics of hydraulic system failures
(1) Debugging stage of new trial equipment
① Serious leakage at joints, fasteners, etc.
② Unstable speed
③ The valve core is stuck or inflexible due to dirt, causing the actuator to malfunction.
④ The damping orifice is blocked, causing the system pressure to be unstable or unable to adjust the pressure.
⑤ Some valve components are missing springs or seals, or even the pipeline is connected incorrectly, causing the action to be mixed.
⑥ Improper design and improper selection of hydraulic components cause the system to heat up, or the synchronous action is not coordinated, and the position accuracy does not meet the requirements.
(2) Finalized equipment debugging stage
① External leakage.
② Unstable pressure or inflexible movement.
③ Dirt enters the hydraulic parts and pipes.
④ Springs or other parts are missing or installed incorrectly inside the hydraulic components.
⑤ Poor processing quality or poor installation quality of hydraulic components, resulting in inflexible movement of the valve core.
(3) Mid-term of equipment operation
When the equipment is running in the mid-term, the failure rate is the lowest, and the hydraulic system is in the best operating state at this stage, but special attention should be paid to avoid oil contamination.
2. Common faults and causes
(1) Excessive oil temperature
① Poor heat dissipation.
The oil tank selected for the system design is too small, resulting in too fast oil circulation; or the ambient temperature is high and a cooler with poor cooling effect is used.
② Poor operation of the system unloading circuit.
Generally, an unloading valve is set at the pump outlet of the hydraulic system. If the unloading valve does not work properly, the oil will overflow from the overflow valve back to the oil tank when the pressure oil is not needed, causing the oil temperature to rise.
③ Impact during switching and speed switching.
④ Air or moisture enters the oil.
When the hydraulic pump converts the oil into pressure oil, if there is air and moisture, the heat will increase and cause overheating.
⑤ Misuse of hydraulic oil with too high a viscosity or hydraulic oil becoming larger.
Hydraulic oil oxidation and low ambient temperature increase the oil viscosity, which increases friction and causes heat.
(2) Vibration and noise
① Hydraulic pump sucks air
The hydraulic system oil level is too low, the oil 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 air-permeable, etc., resulting in the hydraulic pump failing to suck oil and generating noise.
② Hydraulic pump damage
During use, due to the wear of hydraulic pump parts such as blades and oil distribution plates, excessive clearance, insufficient flow, excessive speed and pressure fluctuations, noise can also be generated.
③ Overflow valve failure
The contaminants in the hydraulic oil block the damping hole, resulting in poor oil flow, deformation of the overflow valve spring, and jamming of the valve core, which can cause overflow valve pressure fluctuations, thereby generating vibration and noise.
④ Mechanical vibration
The most common is pipeline jitter and unbalanced vibrations caused by the rotating parts of the motor and hydraulic pump.
(3) Hydraulic system leakage
① Poor lubrication between moving parts, improper material selection, and poor processing, assembly, and installation accuracy lead to early wear, increased clearance, and increased leakage.
② Leakage due to poor sealing effect caused by poor sealing materials, unstable physical and chemical properties, low mechanical strength, low elasticity and wear resistance.
③ Unreasonable design of the groove size for installing seals.
④ The surface roughness value of the joint surface is large, the flatness is poor, deformation after pressure, and uneven tightening force cause leakage.
⑤ Leakage caused by oil leakage from components and blocked oil return lines.
⑥ Leakage caused by excessive oil temperature, decreased oil viscosity, or too low oil viscosity.
⑦ Defects in the hydraulic casting housing cause increased leakage.
3. Solutions to common faults
（1）Oil temperature is too high
If the oil temperature in the hydraulic system is too high, it will lead to the following consequences: the viscosity of the oil will decrease and leakage will increase; the oil will deteriorate and block the gaps of the hydraulic components, and oxidizing substances will be produced, blocking the gaps of the hydraulic components, making the components unable to work normally; it will cause mechanical thermal deformation and destroy its original precision.
（2）Solution to high oil temperature in hydraulic system:
① Design a tank of sufficient size and install a cooler if necessary. When the ambient temperature is too high, isolate the system from the outside world and strictly control the system temperature within the range of 20-60℃, and the maximum should not exceed 70℃.
② When high-pressure oil overflows from the overflow valve to the tank for a long time, the design should be improved, and a variable pump or a correct unloading method should be used.
③ The pipeline should be shortened as much as possible, not too slender or curved, and the oil should flow smoothly as much as possible.
④ The hydraulic pump and its joints should be sealed in places prone to leakage, and the connectors should be tightened to avoid volume loss and heat.
④ When the setting value of the pressure regulating valve is too high, it is best to reduce the working pressure to reduce unnecessary energy loss.
⑤ Choose hydraulic oil with appropriate viscosity.
4. Solutions to vibration and noise in hydraulic systems
① For cavitation, an exhaust device can be installed on the hydraulic cylinder. Or after the equipment is started, the actuator can be exhausted several times with a fast full stroke.
② When the hydraulic pump cannot suck oil, strengthen the oil inlet seal; The height from the oil suction pipe to the pump suction port is required to be less than 500mm; select hydraulic oil with appropriate viscosity.
③ Pay attention to the cleaning and inspection of the overflow valve, and repair or replace it in time if it is damaged.
④ When mechanical vibration occurs, when the oil pipe is slender and has many elbows, you can add a fixed pipe clamp and adjust the installation accuracy of the motor and hydraulic pump to no less than 0.1mm.
5. Solution to hydraulic system leakage
Compared with other faults, leakage is more intuitive and can be found through visual inspection.
The solution is:
① The machining accuracy and matching clearance of the kinematic pair with gap seal should be strictly controlled; improve the sealing device, such as replacing the “V” seal at the piston rod with a “Yx” seal ring, which not only has low friction but also reliable sealing.
② Minimize the number of oil pipe joints and flanges.
③ Installing the hydraulic valve table in the hydraulic system close 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 the system pipeline joints to loosen and leak.
⑤ The leakage amount is inversely proportional to the viscosity of the oil. The smaller the viscosity, the larger the leakage amount. Therefore, the hydraulic oil should be replaced in time according to the temperature to reduce leakage.
⑥ Control the temperature rise.
