1. Internal and external leakage of hydraulic system
Hydraulic system leakage can be divided into two types, one is internal leakage, the other is external leakage.
(1) External leakage
A leak in a pressure line can be easily detected because the leaking hydraulic fluid can be seen. Maintenance personnel and operators should check every component of the entire hydraulic system frequently to detect leaks and address them immediately. However, when external leakage occurs at the suction port of the pump, it is difficult to detect. If one of the following 5 phenomena occurs, the system suction pipe leakage can be suspected:
1) There are air bubbles in hydraulic oil;
2) The hydraulic system is unstable and crawling;
3) Overheating of hydraulic system;
4) Increased tank pressure;
5) Pump noise increases.
If any of these conditions are present, all suction tubing joints and connections should be inspected first for leaks. Do not over-tighten the hose joint, because excessive tightening will deform the joint and increase leakage. The torque value recommended by the equipment manufacturer should be used, which will ensure a reliable seal and will not cause the joint and the sealing ring to distort and cause damage to the sealing ring surface.
(2) Internal leakage
Due to the wear and tear of the components in the hydraulic system, the leakage within the components will become more apparent over time. Minor internal leakage may not be detected, but as internal leakage increases, overheating of the system will become a problem. When this happens, other components of the system will begin to fail. A simple way to identify internal leaks is to test the system's full and no-load operating cycles. If it takes much longer to complete the load operation than the no-load operation, it is suspected that the pump may have failed.
Once the hydraulic components in the hydraulic system leak, it will not only cause the waste of media and environmental pollution, but more serious will make the whole hydraulic system failure, stop working, resulting in safety and quality accidents.
In order to reduce the failure of the hydraulic system, improve the efficiency of the hydraulic system, prevent environmental pollution and reduce the loss of the hydraulic medium, we must pay attention to the leakage problem, and analyze the causes of leakage, take corresponding measures to reduce the leakage and avoid the purpose of leakage.
2. Related factors causing leakage
1) Working pressure. Under the same conditions, the higher the pressure of the hydraulic system, the greater the possibility of leakage, so the size of the system pressure should be in line with the optimal value required by the hydraulic system, so as to not only meet the requirements of the work, but also avoid unnecessary high system pressure.
2) Operating temperature. Most of the energy lost by the hydraulic system is converted into heat energy. Part of this heat energy is sent to the atmosphere through the surface of the hydraulic components themselves, pipelines and fuel tanks, etc. The rest is stored in the hydraulic oil, making the oil temperature rise. The rise of oil temperature will not only reduce the viscosity of the oil, increase the amount of oil leakage, but also cause the acceleration of the aging of the sealing element, early failure, causing serious leakage.
3) Oil cleaning procedures. The hydraulic oil of the hydraulic system often contains various impurities, such as the installation of hydraulic components is not cleaned, attached to the above impurities such as iron filings and paint into the hydraulic oil; Dust and dirt that invade hydraulic equipment contaminate hydraulic oil; The colloid, asphaltene and carbon slag produced by oxidation and metamorphism of hydraulic oil. The impurities in the hydraulic oil can aggravate the wear of the sliding surface of the hydraulic components, the spool of the hydraulic valve is blocked, the hole is blocked, the seal is damaged, and so on, resulting in the damage of the hydraulic valve and the leakage of the hydraulic oil.
4) Selection of sealing device. It is very important to choose the sealing device correctly to prevent the leakage of hydraulic system. The reasonable selection of the sealing device can improve the performance and efficiency of the equipment, prolong the service life of the sealing device, so as to effectively prevent leakage. Otherwise, the sealing device does not adapt to the working conditions, resulting in premature wear or aging of the sealing elements, it will cause medium leakage. In addition, the processing accuracy of the hydraulic components, the firmness of the connection of the hydraulic system pipeline and its vibration resistance, the maintenance of the equipment, etc., will also affect the leakage of the hydraulic equipment.
3. Leakage prevention
1) Control the pressure. The working pressure of the system should be determined according to calculation at the time of design, and should not be adjusted or changed casually in the process of use.
2) Control the temperature change. To control the temperature rise of hydraulic system, the design of oil tank and the setting of hydraulic pipeline are generally started. To improve the heat dissipation effect of the oil tank, you can increase the heat dissipation surface of the oil tank and separate the oil output and return inside the oil tank with a partition. The temperature of the hydraulic oil in the tank is generally allowed to reach 55°C ~ 65°C, and the maximum is not more than 700 °C. When the natural cooling oil temperature exceeds the allowable value, it is necessary to add cooling water pipe inside the tank or set a cooler on the oil return circuit, so as to reduce the temperature of the hydraulic oil. The hydraulic pipeline should be set so that the distance between the tank and the actuator may be short, and the elbow of the pipeline, especially the 90° elbow, should be as few as possible to reduce pressure loss and friction.
3) Keep the cleanliness of hydraulic oil. The oil filter device is used to filter the hydraulic oil regularly or continuously, so as to reduce the impurity content of the hydraulic oil as far as possible and ensure that the cleanliness of the oil meets the national standard.
4) Choose the sealing device reasonably. In order to choose the sealing device reasonably, we must be familiar with the form and characteristics of various sealing devices, the characteristics of sealing materials and the use conditions of sealing devices (such as the size of the working pressure, the temperature of the working environment, the speed of the moving part, etc.). Comparing the actual service conditions with the allowable service conditions of the seals, it is necessary to ensure that the seals have good sealing performance and long service life.
5) In daily maintenance, it is necessary to strengthen the inspection of equipment and conduct regular testing of hydraulic oil to ensure that the oil quality is clean and in line with standards. Choose the durable sealing device that meets the standard, replace the sealing device regularly or periodically, strengthen equipment maintenance, minimize leakage, and ensure the normal operation of hydraulic equipment.
6) The correct selection of the sealing device is very important to prevent the leakage of the hydraulic system. The reasonable selection of the sealing device can improve the performance and efficiency of the equipment, prolong the service life of the sealing device, so as to effectively prevent leakage. Otherwise, the sealing device does not adapt to the working conditions, resulting in premature wear or aging of the sealing components, which will cause medium leakage.
In addition, the processing accuracy of the hydraulic components, the firmness of the connection of the hydraulic system pipeline and its vibration resistance, the maintenance of the equipment, etc., will also affect the leakage of the hydraulic equipment.
