Stacked filter unit

Cahill, T.A. Eldred, R.A. Barone, J.B. Ashbaugh, L.L. "Ambient Aerosol Sampling with Stacked Filter Units" Federal Highway Administration Report No. FHWA-RD-78-178, 1979. 

It should be noted that the sampler used in the study, (a stacked filter unit), collected only particles less than 15pm aerodynamic diameter, i.e. particles of respirable size. State standards for TSP are based on High Volume samplers which have no inlet cutoff. Hence, particles as large as 100 microns can be captured by these instruments. Therefore, measurements made in this study may not indicate whether particulate standards have been violated, since a significant portion of the total suspended particulate mass is not measured by the stacked filter unit (SFU). 

The particle sampler chosen for this study was the Stacked Filter Unit (SFU) described by Cahill e al (, ) Particle collection in two size fractions was achieved by placing two Nude-pore membrane filters in series. The first filter, with 8pm... 

A second way to achieve collection of coarse- and fine-mode particles onto filters is through tandem filtration through the stacked filter unit (SFU) (4, 5, 6). In these devices, the convenient filtration characteristics of filters (Nuclepore) allow a 2.5- xm cut point on the basis of pore size and the face velocity of the airstream. Such devices are very compact and inexpensive and have been heavily used in remote-area networks (7, 8, 9). Again, however, the limitations of the method limit the number and sharpness of the size cuts so that almost all units are operated at 2.5 xm and give coarse and fine fractions very much like those of the virtual impactor. Examples of the 2.5- xm cut points of VI, SFU, and impactors are shown in Figure 2. However, cyclones, virtual impactors, and stacked filter units cannot give the sharp, multiple cut points of impactors as shown in Figure 1. 

Size separation of particles can be achieved by filtration through successively smaller filters in a stacked filter unit. Another approach uses the virtual impactor, a combination of an air filter and an impactor (discussed below). In the virtual impactor, the gas stream being sampled is forced to make a sharp bend. Particles larger than about 2.5 pm do not maJce the bend and are collected on a filter. The remaining gas stream is then filtered to remove smaller particles. 

Fine and coarse aerosol particles were sampled using stacked filter units (SFU) 20). The SFU was fitted with a specially designed inlet, which provided a 50 % cutoff diameter of 10 pm (27). The SFU collects coarse mode particles... 

The AFA is common to the ERB and the APB and consists of 10 filter units, 8 in operation and 2 in standby. Each filter unit consists of a particulate prefilter, a HEPA filter, an activated carbon filter for removal of agent vapor and volatile organic compounds (VOCs), five backup activated carbon filters in the event of breakthrough, and a final HEPA filter. Filtered air is exhausted into a common header and ducted to a common stack. There will be secondary waste in the form of spent activated carbon and filter media. 

Electrode plates or grids are assembled in stack of cells (see Fig. 2). There is no membrane separation between the electrodes. The electrodes are inserted inline directly into the water flow after the filtering unit. Monopolar, bipolar, and combined bipolar-monopolar electrode configurations are used. The required maximum chlorine production rate, for residential pools 2-3 g of CI2 per hour per 10 m of water, defines the size and number of cells. 

There are three common types of filters rotary precoat filters, cartridge filters, and stacked paper plates. In practice, paper plates are best. In particular, Sparkler stacked filters are easy to maintain. Operation of rotary precoat fillers is too complex for many refinery applications. Cartridge filters are good, except that the cartridge cost can be high when frequent change-outs are necessary. Stacked paper plate filters are quite simple The paper is discarded after each use. On one unit it was estimated that 1,000 lb of particulates had accumulated in one 50-plate Sparkler filter. 

Figure 8.12 Two types of electrotransfer apparatus. At the left a tank transfer cell is shown in an exploded view. The cassette (1) holds the gel (2) and transfer membrane (3) between buffer-saturated filter paper pads (4). The cassette is inserted vertically into the buffer-filled tank (5) between positive and negative electrodes (not shown). A lid with connectors and leads for applying electrical power is not shown. On the right side of the figure is shown an exploded view of a semidry transfer unit. The gel (5) and membrane (6) are sandwiched between buffer-saturated stacks of filter paper (4) and placed between the cathode assembly (3) and anode plate (7). A safety lid (1) attaches to the base (9). Power is applied through cables (8).

The formation of the transfer unit starts with the anodic filter paper stack. Two to three sheets of filter paper are soaked in buffer A and placed onto the anode. Air bubbles are removed using... 

Figure B3.2.2 Electroblotting with a tank transfer unit. The polyacrylamide gel containing the protein(s) to be transferred is placed on the smooth side of the polyethylene sheet (or filter paper sheets) and covered with the PVDF membrane and then a single sheet of filter paper. This stack is sandwiched between two fiber pads and secured in the plastic gel holder cassette. The assembled cassette is then placed in a tank containing transfer buffer. For transfer of negatively charged protein, the membrane is positioned on the anode side of the gel. Charged proteins are transferred electrophoretically from the gel onto the membrane.

Figure B3.2.3 Electroblotting with a semidry transfer unit. In most cases, the lower electrode is the anode, as shown. Position the Mylar mask (optional) directly over the anode. Layer on three sheets of filter paper that have been wetted in transfer buffer. For negatively charged proteins, place the preequilibrated transfer membrane on top of the filter paper followed by the gel and three additional sheets of wetted filter paper. If multiple gels are to be transferred, separate the transfer sandwiches by inserting a sheet of porous cellophane or dialysis membrane between each stack. Place the cathode on top of the assembled transfer stack(s). Transfer the proteins by applying a maximum current of 0.8 mA/cm2 gel area.

The ED stack is the unit holding together anionic and cationic membranes assembled in parallel as in a filter press between two electrode-end blocks in such a manner that the stream undergoing ion depletion (i.e., the diluate or diluting stream) is kept separated from the other solution (concentrate or concentrating stream) undergoing ion enrichment. Figure 4 shows an exploded view of it. 

Horizontal Diaphragm Presses This is similar to the diaphragm press except the filter plates lay horizontally (while in diaphragm press, the filter plates are operated vertically). The press can be a singlechamber unit, or multiple chambers can be stacked to achieve greater filtration area. 

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