Filter media perforated plate

Strainers offer a simple method for the protection of pipeline systems, by removing debris such as dirt, swarf, weld sputter, scale and so on. They are simple coarse filters using perforated plate or wire mesh as the filter medium. Strainers fall broadly into two categories temporary strainers and permanent strainers. 

The hltration medium may be made of perforated plates, septum of woven materials, or of granular materials such as sand. Thus, according to the medium used, hlters may also be classihed as perforated plate, woven septum, or granular filters. The hltration medium of the microstrainer menhoned above is of perforated plate. The hlter media used in plate-and-frame presses and vacuum hlters are of woven materials. These units are discussed later. 

Perforated filter— Filter whose filtering medium is made of perforated plates. Plate-and-frame press—A pressure filter in which the mechanics of filtration is through cloths wrapped on a plates alternated and held in place by frames. 

The term nutsche is derived from the German word for sucking. Vacuum is applied at the bottom of a vessel that contains a perforated plate. A filter cloth, screen, perforated plate, or porous ceramic plate may be the direct filtration medium (see Fig. 8). Subsequently, products should have lower cake resistances and well-defined crystal structures to facilitate separation. The driving force for the separation is vacuum and/or pressure. 

Bed filters. The simplest type of filter is the bed filter shown schematically in Fig. 14.2-2. This type is useful mainly in cases where relatively small amounts of solids are to be removed from large amounts of water in clarifying the liquid. Often the bottom layer is composed of coarse pieces of gravel resting on a perforated or slotted plate. Above the gravel is fine sand, which acts as the actual filter medium. Water is introduced at the top onto a baffle which spreads the water out. The clarified liquid is drawn out at the bottom. 

Continuous layer filtration involves filtering the sugar syrup through a layer of activated carbon. Several types of filters are used, such as pressure leaf filters with metal frames on which a filter cloth that may be cotton, polyamide, or wire mesh is fixed rotary leaf filters or bed filters in which the filtering medium is a ceramic or sintered plate, wire mesh, or finely perforated metal plate. The latter filters are usually coated with a layer of filter aid that may be a diatomaceous earth. A suspension of active carbon in water or liquor is passed through the filter until a uniform layer of active carbon bed 10 to 15 mm thick builds up. The filter is then ready for filtration of the liquor that must flow to the filter at a uniform rate to avoid breaking the layer. 

The liquid is passed under centrifugal force through a filter medium or perforated plate. Filtration occurs as the liquid passes through the interstices of the solid particles that have built up on the medium surface. Depending upon the degree of separation desired, fdter media can be a filter fabric of twilled weave, dutch weave or plain weave in either stainless steel or synthetic fibre. 

The Nutsche filter is a vertical vessel, divided into two chambers by a horizontal perforated plate roughly at its mid-point. This plate may itself be the filter medium, or a sheet of finer medium may be laid onto the plate. In its simplest form, the upper chamber of the filter is an open feed chamber, into which the feed suspension is poured or pumped. The enclosed lower chamber is the filtrate receiver, to which the vacuum connection is made (at a level above that of the top of the batch of filtrate) to draw the filtrate through the filter medium, leaving the suspended solids from the feed as a cake on the upper surface of the filter medium. This cake will then be dug out of the filter, or lifted out on a removable filter medium, or tipped out by turning the whole filter unit through 180°. 

The actual medium in a pleated cartridge will have protective mesh (wire or plastic) on its inside and outside, the whole being further protected by a cylindrical perforated plate screen external to the pleats (Figure 3.51). This figure also shows the end-caps sealed to the top and bottom of the pleats to make a coherent filtering element. 

Pneumatic cleaning devices, or air tables, are applied to the small fractions (less than 3/8 in.). In these devices, currents of air flow upward through a perforated bottom plate over which a layer of coal passes. The extreme fines are entrapped in the air and must be recaptured by cyclones and bag filters for return without quality improvement. As the coal reaches the end of the tables, the bottom layer is heavy (high-ash) material, a center layer is medium-weight coal and bone (high-ash), and the top layer is coal (low-ash). The middle layer must be incorporated with the refuse (and rewashed) or with the coal. 

High-volume cascade impactors This technique consists of a stack of five 30 cm-diameter plates, each with 300 jet orifices, mounted over a standard high-volume glass fiber filter. The collection medium is perforated sheets of aluminum foil or glass fiber mounted on aluminum plates. Particle size fractions greater than 7 pm and less than 1.1 pm are collected at a flow rate of 0.561 min... 

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