The working principle of hydraulic oil filter element of return pipe is mainly based on the principle of filtration and separation, which is as follows:
### Filter the impurity particles
- ** Physical interception ** : when the return oil in the hydraulic system enters the filter through the return pipe, the small pores on the filter element will block and intercept impurities and pollutants in the hydraulic oil, such as metal scraps, rubber impurities, dust, etc. The size of these impurity particles is usually larger than the size of the filter pore, so it cannot pass through the filter, thus achieving the separation from the hydraulic oil [^1^][^2^][^3^].
- ** Adsorption ** : Part of the filter material has a certain adsorption, can adsorb small particles and colloidal substances in the hydraulic oil, further improve the filtration effect. For example, the filter element made of some fiber materials can adsorb water and acid substances in the oil to prevent its corrosion to the hydraulic system [^4^].
### Keep the oil clean
- ** Removal of contaminants ** : The clean hydraulic oil filtered by the filter element returns to the tank of the hydraulic system from the outlet pipe and continues to participate in the circulation of the system, thus maintaining the cleanliness of the hydraulic oil, extending the service life of the hydraulic oil, and also reducing the risk of hydraulic components wear and failure due to pollution [^1^][^2^][^4^].
- ** Stable system performance ** : Clean hydraulic oil can make the pump, valve, cylinder and other components of the hydraulic system work normally, ensure the control accuracy and response speed of the system, improve the stability and reliability of the hydraulic system, reduce the maintenance cost of equipment [^2^][^4^].
### Indicator and alarm function
- ** Differential pressure indicator ** : The return filter is usually equipped with differential pressure indicator or differential pressure alarm device. When the flow resistance increases due to the blockage of the filter element, the pressure difference between the inlet and outlet of the filter will reach a certain value. At this time, the indicator or alarm device will send a signal to remind the operator to replace or clean the filter element [^1^][^2^][^3^].
- ** Flow monitoring ** : Some advanced oil return filters can also be equipped with flow sensors to monitor the flow of oil return in real time. When the flow rate changes abnormally, it may be caused by filter plugging or other system failure, and the operator can take corresponding measures in time according to the flow monitoring data [^5^].