High Efficiency Particle Filter(HEPA) Test Methods
Sodium Flame method
From United Kingdom, China prevailing, parts of the European countries in the 1970s and 1990s to implement.
Test dust source is a single dispersed sodium salt spray. “capacity” of the brightness of the flame when the hydrogen-containing salt spray. The main instrument for the photometer.
Stir in the salt air splash, salt spray dried to form tiny and into the duct. Each sample before and after the filter, the hydrogen salt fog like blue flame color, brightness increases. Salt spray flame brightness to determine the concentration of the air, and so determine the efficiency of filters salt spray.
Salt spray particles have an average diameter of national standards for 0.4μm, but the actual results of the existing domestic device is 0.5μm. Europe on the actual test measurements salt spray particle diameter of 0.65μm.
With the popularity of scanning, Europe is no longer using the sodium flame method. Domestic authorities are revising the existing national standards, is abolished or continued use of sodium flame method, there are two opinions, but there is no conclusion.
Standards: UK BS3928-1969, the European Eurovent 4/4, Chinese GB 6165-85.
From the United States,International general, China has never practiced.
Test dust source is 0.3μm monodisperse DOP ( plastics industry used plasticizer ) droplets. "Quantity" DOP concentration containing turbid air . Dust measuring instrument for the photometer (photometer). In order to determine the differences in gas samples muddy efficiency filters DOP particles.
Heating the liquid to stay on the DOP particles of about 0.3μm steam, condensed into fine droplets under certain conditions , to remove too large and small droplets , the DOP mist into the air duct . Gas samples before and after the filter turbidity measurements , and thus determine the filter of 0.3μm dust filtration efficiency.
DOP has 50 years of history, this method was the most efficient filters commonly used method to measure the world. Early on, people think 0.3μm dust filter for filtering the hardest , and therefore require the use of 0.3μm dust measuring efficiency filter .
DOP containing benzene change , people suspect it carcinogenic , many laboratories use similar performance but substitutes contain benzene , such as DOS, but the test method is still called "DOP law ."
By changing the parameters of dust , you can get the other size of the DOP droplets. So there 20 years ago, the U.S. and Europe to measure ultra- high efficiency filter of 0.1μm DOP method, sometimes measuring instruments also changed condensation nuclei laser particle counter . Some foreign manufacturers have indicated to 0.05μm or 0.03μm DOP fees filtration efficiency, and that is no scientific basis for the commercial unconventional.
Measuring efficiency filter of DOP Act , also known as "hot DOP law ." Dust and more dispersed DOP case corresponding " cold DOP" refers Laskin nozzle ( bubbled with air bubbles in the liquid , dust and spatter Human mist ) generated in the scan test the filters , often use cold DOP.
Counting scanning method
Europe general , like the United States, followed by other countries . Mainstream international test methods currently high efficiency filter .
The main measuring instruments for the large flow or condensation and laser particle counter counter (CNC). Counter on the outlet side of the filter to scan checkout counter every point given the number and size of dust . This method can not only measure the average efficiency of the filter , can also compare the efficiency of the local points .
European experience shows that for high efficiency filter , most likely to penetrate the dust particle at a certain point , the first test between 0.1 ~ 0.25μm most easily penetrate the dust particle , and then continuously scans the measurement of particle filters dust filtering effect , the Europeans will this method is called MPPS. American Standard requirement altogether measure only 0.1 ~ 0.2μm range.
Multiple sources of dust dispersed droplets used in the experiments was generated Laskin nozzle , or to determine the particle size of the solid dust . Sometimes , manufacturers require special filters require the installation of users, the use of atmospheric dust or other specific dust. If the test is used in the condensation and the counter , it must be aware of the monodisperse particle size of test dust .
Surface with a sweeping counter filter takes a long time . To save time, foreign to four groups large flow sampling head and laser measuring devices into one, which makes the detection speed is greatly improved, but the detection rate of a scanning station still keep up with the production rate of a common filter production line , so the mainstream filters plants often need to configure several scanning devices.
Counting scanning efficiency filter is the most stringent test methods , this method is an alternative to other methods of traditional trend .
Standards : European EN 1882.1 ~ 1882.5-1998 ~ 2000, the United States IES-RP-CC007.1-1992.
Dust source is generally multi-dispersed droplets, as Laskin nozzle produced DOP smoke. Use a filter photometer low overall scan leak. This scanning method can quickly and accurately locate the filter leak. As the dust source as much dispersed, and photometer dust particle can not be determined, so this scan gives “filtration efficiency” of little practical significance.
Some manufacturers and users believe that, as long as the quality and specifications of the filter paper tightly controlled, the efficiency of the filter has been determined, therefore, to be only for the purpose of scanning leak can guarantee the quality of the filter.
Photometer scanning method does not leak the corresponding standard to follow, but this method of quality control of the production process is very effective, the test equipment used is relatively simple, so some manufacturers are currently using this method. Photometric scan test station is easily scanned into counting stations, spend money too laser particle counter on it.
Oil Mist method
Former Federal Republic of Germany, the former Soviet Union, China.
Dust source of oil mist. "Quantity" of oil mist air turbidity. Equipment for the turbidity meter. Turbidity difference in gas samples to determine the efficiency of filters for oil mist particles.
In Germany, the use of paraffin oil, mist particle size of 0.3 ~ 0.5μm. Chinese standards mist mean weight diameter of 0.28 ~ 0.34μm, on the type of oil without making specific provisions.
Mist to find the German domestic law has become history, Germany took the lead in 1993 to come up with a national standard counting scanning method, the European standard EN1882 is the German technical standards modeled scanning method developed.
Although the Chinese standard method can be used to mist, but the domestic manufacturers are more willing to use the same standards for another sodium flame method.
Standards: Chinese GB 6165-85, Germany DIN2484-1990.
Only the French use is currently limited to the nuclear industry of the filter test .
Sodium fluorescein powder spray dust test dust source is generated . The experiment, the sample before and after the filter , and then dissolved in water and sodium fluorescein filter on the sample , the measurement is more aqueous sodium -containing fluorescein fluorescence intensity , and indirectly reflects the luminance weight of dust under certain conditions . Difference in fluorescence intensity before and after the filter samples to determine the filter efficiency.
According to the French count mean standard device generates dust dust particle size of 0.08μm, volume mean particle size of 0.15μm.
Fluorescence is too much trouble , you need to adopt the measurement , the sample cleaning , then went to another place to test the fluorescence. Indeed, the French past the filter plant is the most commonly used DOP law , rather than their own requirements fluorescence, and now the French have positioned the national standard, fluorescence utterly useless European Association for Standardization count scanning. But when it comes to nuclear grade high efficiency filter , in order to meet the requirements of customers tradition 20 years ago , they only use the fluorescence method.
Standards : French NF X44-011-1972.