Fine filters

Depending on the test method and test result, particle filters are classified as coarse, fine, HEPA, and ULPA filters (Table 9.2). Electrofilters are usually included in the fine filter group. Chemical filters are used for gases. 

Fine filter, 0.4 im efficiency Fine filter, dust spot efficiency Average ( ) efficiency, % ... 

Fine filters are made chiefly from glass fibers with an average diameter of 0.5 pm to 5 pm or of plastic fibers, often in combination with an electrostatic... 

A new fine filter in the lower fine-filter range, F5 (EU5), separates about 20% of all particles in the air, whereas a better fine filter, F8 (EU8), can take 80% to 90%. 

Coarse A filter positioned before a fine filter to remove the larger particulates in order to extend the operating time of the fine filter. Cylindrical A filter contained in a cylindrical form. 

Prefilter A rough filter positioned before a fine filter to reduce clogging of the fine filter. 

Lubrication is needed to reduce friction and provide cooling. Lubricating oil, which must be finely filtered to prevent grit from entering the... 

Reliable enclosed filters of ample effective filtering area should be used for both stages. The filter design should not allow the pressure drop to exceed 7kN/m (1 Ibf/in ) across second-stage fine filters in clean conditions. Filters should preferably be of the duplex or self-cleaning type, and installed so that oil spillage will not occur during operation. 

Provided that the system is initially clean and fitted with efficient air filters, metal edge-strainers of 0.005-inch spacing appear to be adequate, although clearances of vane pumps may be below 0.001-inch. It should be remembered that an excessive pressure drop, due to a clogged full-flow fine filter, could do more harm to pumps by cavitation than dirty oil. 

The clarity of the final beverage is affected by small particles of tartrates and other substances which precipitate during storage. To obtain a product which will remain clear in storage, many wines and spirits are cooled by refrigeration to a temperature just above their freezing points and then fine-filtered. 

Finer filtration is possible, down to 0.01 jXn. Such filter elements are only used when the process demands this high standard. These fine filters would clog quickly with normal-size impurities, so they usually have a coarser filter upstream, to take out the larger dusts. They are about 300 mm deep, and require special mounting frames so that dirty air cannot escape around the edges. 

Fig. 139. Plasma chemical installation. 1 - Plasma generator 2 — plasma torch 3 - pneumatic nozzles 4 — reactor 5 - solid parts collector 6 — fine filter 7 - heat exchanger 8 - condensate collector.

Procedure. The solution should not exceed 50 mL in volume, all metallic elements should be present as nitrates, and the cerium content should not exceed 0.10g. Treat the solution with half its volume of concentrated nitric acid, and add 0.5 g potassium bromate (to oxidise the cerium). When the latter has dissolved, add ten to fifteen times the theoretical quantity of potassium iodate in nitric acid solution (see Note) slowly and with constant stirring, and allow the precipitated cerium(IV) iodate to settle. When cold, filter the precipitate through a fine filter paper (e.g. Whatman No. 42 or 542), allow to drain, rinse once, and then wash back into the beaker in which precipitation took place by means of a solution containing 0.8 g potassium iodate and 5 mL concentrated nitric acid in 100 mL. Mix thoroughly, collect the precipitate on the same paper, drain, wash back into the beaker with hot water, boil, and treat at once with concentrated nitric acid dropwise until the precipitate just dissolves (20-25 mL... 

An unknown amount of the substances described above were lost in the oil and gravel separator and by flushing of the fine filters. An attempt to make a full mass balance failed. 

When shaking is complete, the suspension is gravity filtered through a standard fine filter paper into a sample container. If the filtrate is cloudy, it can be filtered through the same filter paper again. If this is not sufficient, the filter... 

To the reaction mixture a small amount of toluene is added and the mixture is filtered off. Toluene is removed by distillation under reduced pressure and the resin is made to heat at 150°C and 5 mm. Hg pressure to remove traces of volatile matter. Finally, the resin is clarified by passing through a fine filter. 

Why must mobile phases and all samples and standards be finely filtered before an HPLC experiment ... 

Dry grids by placing on fine filter paper, i.e., Whatman no. 50. 

The 20/80 PHBA/diol ratio oligomer was soluble in MIBK. The 30/70, 60/40, 50/50 and 40/60 oligomers form stable, milky dispersions in MIBK. For example, a roughly 12% "solution" of the 40/60 diol was slightly milky, yet it readily passed through fine filter paper (Whatman 42). A 70% dispersion of this oligomer in MIBK retained its milky appearance for more than one year. No precipitate separated. 

Dirt in oil. This is a common cause of failures, especially when combined with other factors. The oil film at the end of the oil wedge is only a small fraction of a thousandth inch thick. If dirt goes through, it can cause the film to rupture, and the bearing may burn out. Therefore, very fine filtering of the oil is required. 

Very fine filters are recommended for ethanol dispensers to ensure that waterborne solids do not contaminate vehicle filters or fuel injectors. Dispensing hoses delivering ethanol and other alcohol fuels to vehicles may be green or blue in color to signify their compatibility with alcohol fuels. Also, blending ethanol with conventional fuels helps to minimize compatibility problems with existing fuel system components. 

Filtration can remove fine suspended solids and microorganisms, and microfiltration membranes of cellulose acetate or polyamides are available that have pores 0.1-20 /xm in diameter. Clogging of such fine filters is an ever-present problem, and it is usual to pass the water through a coarser conventional filter first. Ultrafiltration with membranes having pores smaller than 0.1 fim requires application of pressures of a few bars to keep the membrane surface free of deposits, water flows parallel to the membrane surfaces, with only a small fraction passing through the membrane. The membranes typically consist of bundles of hollow cellulose acetate or polyamide fibers set in a plastic matrix. Ultrafiltration bears some resemblance to reverse osmosis technology, described in Section 14.4, with the major difference that reverse osmosis can remove dissolved matter, whereas ultrafiltration cannot. 

Keep containers covered to avoid dust, which scatters light and appears to the spectrophotometer to he absorbance. Filtering the final solution through a very fine filter may be necessary in critical work. Handle cuvets with a tissue to avoid putting fingerprints on the faces—fingerprints scatter and absorb light—and keep your cuvets scrupulously clean. 

These factors combine to make impactors less precise and accurate than filters. Very few comparisons have been made between sizing impactors and those that have provided mixed results. The 1977 Environmental Protection Agency-Department of Energy Sampler Intercomparison included the Multi-Day Sampler, which performed well ( 15%) for fine aerosols such as sulfur, lead, and zinc (15). The 1986 Carbonaceous Species tests at Glendora, California, included the DRUM sampler. It performed well for sulfur ( 18%), as compared to the fine filter sampler (PM-2.5), but no other sizing impactor was available for comparison and no element other than sulfur was reported. DRUM versus filter comparisons were reported as part of the Southern California Air Quality Study of 1987 (2). Again, no other impactor was available for comparison, and the comparisons with filters were only fair (r2 0.7 r, linear correlation coefficient). 

Thus the filtration resistivity of the medium includes its thickness. Typical measured values of Rf are of the order of 10lom-1 for comparison, the fine filter sheet of Table 1.6, assuming it to be 1 mm thick, has LIKP =0.001/0.15(1(T12) = 0.7(1010) m1. 

The vehicles designed to use ethanol as a fuel tend to have very fine filters to protect their fuel injectors and other components from corrosion products. 

Filtration The process of separating a solid from a liquid using a fine filter paper which does not allow the solid to pass through. 

The air is passed through fine filters to remove dust. 

If the pump does not deliver solvent, do not immediately assume that the plunger is broken. Open the compression fitting at the top of the check valve to release pressure. Pressurize the inlet line with a syringe full of solvent and turn the pump on. Often, an air bubble will cause the pump to cavitate and stall. This is often a problem with pumps having fine filters in the inlet check valve. This technique should cause air bubbles to come out of the outlet fitting. Simply reseat the compression fitting and go back to work. 

Microfilters are used in the electronics industry, principally as final point-of-use filters for ultrapure water. The water is already very pure and almost completely particle- and salt-free, so the only potential problem is contamination in the piping from the central water treatment plant to the device fabrication area. Although fine filters with 0.1 pm pore diameter or less may be used, lifetimes are relatively long. 

The rate of reduction of cupric ion is illustrated in Fig. 3 (1). Curve 21 represents the hydrogen pressure drop observed in a typical experiment. Curve 23 is a repetition of this reduction, starting, however, with the reduced solution of experiment 21, which was oxidized by molecular oxygen from a red reduced solution to a green oxidized one. The final slopes (reduction rate) are the same for 21 and 23, the only difference being that 23 has a much longer induction period. If the reaction is stopped just before the flat portion of the curve (21 and 23) is reached and the solution filtered through a fine filter paper, no precipitate is found. 

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