Test method and principle of filter leakage

1 HEPA filter HEPA: high efficiency particulate air means "rate air particle filtration" HEPA indicator, defined as: for particles with a particle size of 0.3 μ m, the filtration efficiency is greater than or equal to 99.97% As mentioned above, when we use the filter, we must express the efficiency together with the experimental method, such as 99.97% (0.3 μ m, DOP), which means that it is tested by DOP experimental method 2) ULPA filter ULPA: ultra low filtration air is a filter with higher filtration level than HEPA It is defined as a filter with particle filtration efficiency of 0.1-0.2 μ m or higher than 99.999% The filter is used in pharmaceutical factory, electronic factory, chip factory, etc it is not used in household appliances Principle of filter leakage detection: DOP aerosol is sent to the windward side of the filter to be tested as the dust source, and a photometer is used to sample and test the downwind side The scattered light generated by the dust gas through the photometer is converted into electricity through photoelectric effect and linear amplification, and it is quickly displayed by the microammeter The collected air sample passes through the diffusion chamber of the photometer, because the particle diffusion causes the difference of light intensity, the light intensity is measured The relative concentration of aerosol can be measured by photometer 5 Test procedure: 5.1 introduce aerosol at the windward side of the filter: 5.1.1 put DOP smoke into the air conditioner directly when stopping system leak detection 5.1.2 when the DOP detector is small, it can be placed in the static pressure chamber of the filter 5.2 immediately scan the outlet side of the filter with the sampling head of the aerosol photometer The interval between the sampling head and the filter is about 2cm The scanning speed should be less than 5cm / s along the inner frame of the filter 5.3 when the reading of photometer exceeds 0.03%, it indicates that the leakage exceeds the standard and needs to be repaired or replaced 5.4 stop scanning and patrol inspection after plugging with epoxy resin silica gel or fastening bolts The company specializes in the design and construction of consumer filter, junior high efficiency air filter, air shower room, transfer window, ultra clean workbench, air supply outlet, FFU and air purification engineering If you have any questions, please consult: the leakage test method of Huang Zhenmin filter 1) sodiumflame method originated from England, which is popular in China, and implemented in some European countries in the 1970s-1990s The dust source of the experiment is single dispersed phase sodium chloride salt spray The "quantity" is the light intensity of characteristic light of hydrogen flame in salt fog The main test instrument is photometer Salt water splashes under the agitation of compressed air, forms a small salt mist through dryness and enters the air duct Before and after the filter, samples were taken respectively, and the salt fog made the color of hydrogen flame blue and brightness increased The flame brightness is used to judge the salt fog concentration of air, and the filter efficiency is confirmed Relevant specifications: China's gb6165-85, at present, the relevant domestic departments are revising the specifications, whether to abolish or continue to have no final conclusion This approach is no longer used in Europe 2) oil mist method was adopted by the former West Germany, the former Soviet Union and China The dust source is oil mist "Quantity" refers to the turbidity of oil mist air The instrument is turbidimeter The filtration efficiency of the filter for oil mist particles can be determined by the turbidity difference of the gas sample The oil mist method used to be a history in Germany Only a small number of military units in China still use the oil mist method, because the former Soviet Union used the oil mist method when helping China with filters Relevant specifications: gb6165-85 in China 3) DOP law originated from the United States and has been internationally accepted The dust source of the experiment was DOP (dioctyl phthalate, a kind of plasticizer commonly used in plastic industry) droplet of 0.3 μ m single dispersed phase "Quantity" is the turbidity level of the air containing DOP The instrument for measuring dust is a photometer According to the turbidity difference of the gas sample, the filtration efficiency of the filter for DOP particles can be determined The DOP liquid is heated to steam, and the steam condenses to 0.3 μ m micro droplets under specific conditions, and the mist DOP enters the air duct Measure the turbidity of the gas sample before and after the filter, and judge the filter efficiency of 0.3 μ m dust DOP method has a history of more than 50 years This method was used to measure Zui filter in the world In the early days, it was thought that the filter was difficult to filter 0.3 μ m dust Zui, so 0.3 μ m dust measurement filter was used regularly DOP contains benzene ring, which is suspected to be carcinogenic, so many laboratories use substitute with similar performance but without benzene ring, such as DOS, but the experimental method is still called "DOP method" The DOP method of measuring filter is also called "hot DOP method" The corresponding "cold DOP" refers to that the nozzle uses compressed air to blow up bubbles in DOP liquid, and splashes to generate fog like artificial dust Relevant specifications: American specification mil-std-282 4) the MPPs law (most transparent particlesize) is applicable to air conditioning filters in Europe, in the United States except for national defense industry, and in some Chinese enterprises It can measure almost all HEPA and ULPA filters, and has the trend of replacing traditional methods It was thought that the filter efficiency Zui of 0.3 μ m dust was low, so when evaluating the filter, the filter efficiency of 0.3 μ m dust was taken as a typical value There are many ways to generate and measure 0.3 μ m dust, so there are such methods as DOP, oil mist, sodium flame, etc
After discussion and experiment, it is found that the laser particle counter, which can measure 0.1 μ m particle size dust, can not only measure the dust concentration, but also the particle size of each dust, so it can easily measure the typical value of low efficiency Zui The dust particle size corresponding to the typical value is MPPs (most permeable particle size, Zui), which corresponds to MPPs The value of low efficiency Zui is MPPs efficiency Relevant specifications: American est-rp-cc-007.1-1992, European en1822-5:2000 5) resistance 1 Definition: when the air flow passes through the filter, the filter will constitute resistance to the air flow, and the air volume will reduce 2 The composition of resistance The resistance of the filter consists of the resistance of the filter data itself and the structural resistance of the filter We hope that the smaller the resistance of the filter, the better, because the greater the resistance, In order to reach the rated output air volume, the power of the motor should be increased If the power of the motor is too small, it will produce a howling sound All these should be solved together, and appropriate filter materials should be selected 3 Initial resistance: the resistance of the new filter is called initial resistance 4 Final resistance: the resistance when the filter is to be scrapped is called final resistance, The selection of the final resistance is directly related to the service life of the filter, the change range of air quality and the energy consumption of the system 5 Unit of resistance: Pascal 1pA = 1n / m2 British unit: inwg inch water column metric unit: mmh2o mmh2o 1mmh2o = 9.8pa inwg = 250pa Objective: through the detection of the leakage of the filter, the defects of the filter and its device are found, such as small pinholes in the filter material, gaps in the joint sealing parts, etc., so as to take timely remedial measures Scope: company clean plant filter leakage inspection Responsibilities: Equipment Engineering Department and quality management department shall be responsible for the implementation of this specification Content: 1 Test method: DOP method; 2 Test scope: 2.1 filter material of filter; 2.2 connection between filter material and its frame; 2.3 connection between gasket of filter frame and support frame of filter group; 2.4 connection between support frame and wall or ceiling 3 Test data and instruments: 3.1 dust source: DOP solvent 3.2 instruments: DOP detector, aerosol photometer Shanghai Sujing Industrial Co., Ltd if you have any need, you can pass with us at any time Thank you very much for your support and look forward to your cooperation Thank you & bestragard! Suing Jinghua