Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Patent
1986-03-03
1988-03-29
Fisher, Richard V.
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
493941, 493966, 2104943, 21049701, 55500, 55521, B01D 2706
Patent
active
047341955
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to manufacturing filter cartridges of the type made from a sheet of filter material, constituted in particular by fibers of resin-impregnated paper which is folded concertina-like round the surface of a cylinder and which has its outer sides received inside two outer supports.
In prior filters of this type, the two main problems currently faced for a given volume and thus an imposed diameter are:
to obtain the maximum effective filter area; and
to avoid some of the concertina folds coming into contact with one another.
It will readily be understood that increasing the filter area reduces the headloss across the filter and thus improves the throughput and the quality of the filtering.
However, the above-mentioned two constraints appear, a priori to be contradictory. This is because increasing the filter surface area for given diameter requires the number of folds that are distributed around the cartridge to be increased, and the folds have to be brought closer together.
Of necessity, the outer face of a filter cartridge is the seat of a fluid flow and of a pressure difference. Thus, it is generally observed on conventional filter cartridges that if the folds of the printer sheet are too close together, some of them come together and aglutinate in bunches whereas others move uselessly apart. As a result:
firstly the effective filter surface area is reduced; and
secondly those filter folds which remain separated on the cartridge are few in number and are rapidly filled with solid dirt. The headloss increases and the cartidge rapidly becomes unusable.
In the more usual cartridges, the folds are merely held by both ends in two end supports which constitutes the flanks of the cartridge.
The initial outer spacing between the folds is about 0.8 mm.
With these usual cartridges, the bunching phenomenon occurs very soon and is highly marked.
The lifetime of the cartridge is very short because of the maximum quantity of dust which can be retained in the few folds which remain effective.
In order to solve this problem, recent prior art has attempted to provide various methods for:
uniformly distributing the folds of the filter sheet round the side surface of the cartridge; and
imposing a minimum distance of about 1 millimeter between adjacent external folds of the cartridge.
A currently implemented first variant consists in crushing the upper periphery of each fold at certain points on the cartridge to increase the width of the fold where crushed and to oblige the folds to stay apart. However, this method does not separate the folds far enough apart. As a result, this method is ineffective.
A second variant, derived from the first, consists in deforming the paper while hot in order to provide its folds with radial ribs which also increase their width and tend to hold them apart. This method ensures an initial degree of uniformity in the fold spacing. However, it is very difficult to implement and requires the use of a special machine. Further, the resulting filter cartridges rapidly lose their mechanical configuration with respect to fold spacing. This is because the hot and chemically difficult environments in which such cartridges operate eliminate the grooves which are hot-formed in the folds. As a result such second variant cartridges return to the defects of conventional cartridges as described above.
Finally, in a third variant filter cartridge an attempt is made to separate the folds uniformly from one another by maintaining them between the successive turns of coil springs, which springs are looped back on themselves and placed on the outer face at different levels all round the cartridge. In this method, the folds are left free except for those places where they are held by the turns of the springs. As a result the bunching phenomenon tends to reoccur between the positions of the springs. To keep the folds apart it is necessary to provide a large number of springs, thereby considerably complicating cartridge manufacture.
Furthermore, the slope of the turns tends to skew the folds
REFERENCES:
patent: 2790207 (1957-04-01), Steele et al.
patent: 3025964 (1962-03-01), Summers et al.
patent: 3112264 (1963-11-01), Bub
Lhuillier Robert
Selesnick Michael
Vieville Jean
Wolfe John
A.R.E. S.A.R.L.
Ferguson Jr. Gerald J.
Fisher Richard V.
Foycik, Jr. Michael J.
Hoffman Michael P.
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