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1. Introduction to filters 1.1 Based on their location of use and purpose, filters can be divided into two categories: strainers and fine filters. Strainers are primarily used in front of pumps, flow meters, and valves to protect these devices from damage caused by large metal particles; their precision is generally above a few hundred microns. Fine filtration is primarily used to purify fluids and ensure process safety. Its precision range is generally between 1 micron and 30 microns. 1.2 According to the requirements of manufacturing design, they can be classified as pressure vessels and non-pressure vessels. Filter housings that are designed and manufactured as pressure vessels shall comply with the GB150 or ASME standards. Non-pressure vessels shall comply with SH/T3411 or HGT 21637 standards. 1.3 Based on the medium used, they can be divided into gas filters and liquid filters. Gas filters are suitable for gas-solid separation applications, and can be used for gas purification, separation, and recovery. Liquid filters are suitable for the field of liquid-solid separation, such as lubricant filtration, filtration in the petrochemical industry, and wastewater treatment. 2. Filtration area of the fine filter: There are three domestic industry standards for coarse filters; therefore, selecting a model in accordance with these standards will meet the requirements. The filtration area of fine filters generally does not require calculation using formulas; the selection is based mainly on experimental data. Therefore, it is recommended to let the manufacturer decide on the filter to be used. The three main curves used for filtration are: the flow pressure difference curve (ΔP-Q), the particle size and filtration ratio curve (μ-β), and the time and pressure curve (T-ΔP). Therefore, when calculating the filtration area, these three curves must be taken into account, with the flow pressure difference curve being the most important; this curve is determined through experiments conducted by reputable filter manufacturers. The current testing method involves multiple passes through the test: the ISO 4572 multiple-pass test standard. At present, in domestic small filter manufacturers, the testing of filter elements is conducted through a single experiment. Steps for calculating the filtration area: 1. Determine the filtration ratio with a filtration precision of 25 microns, such as 200 (filtration efficiency), and decide on the type of filter media to use. 2. Perform a flow pressure difference test on the filter media using a given pressure drop of 0.05 MPa. Determine the appropriate flow rate (L/min). 3. Based on the obtained flow rate, divide it by the area of the test filter material to calculate the flow velocity (L/min·m2). 4. Determine the filtration area based on the flow rate and the flow volume required in practical applications; flow volume/flow rate = filtration area. 5. Determine the structure of the filter element—folded or cylindrical wound—based on the selected filtering area and filter material.