Liquid purification or separation – Processes – Separating
Reexamination Certificate
1998-09-30
2001-03-20
Savage, Matthew O. (Department: 1723)
Liquid purification or separation
Processes
Separating
C073S061640
Reexamination Certificate
active
06203713
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a filter element and a filter device for purifying water that is or may be infected by microorganisms and rendering it potable and to a method for purifying water by means of such filter device, in the most efficient manner.
BACKGROUND OF THE INVENTION
In many localities, no sale and reliable water supply is available. A water distribution system may be lacking, or, frequently, such a system may exist but deliver water that is not or may not be safe and fit for drinking because it is contaminated, particularly by microorganisms. The problem of providing safe, potable water in such localities, has received wide attention and found a variety of solutions in the art.
Filtration is one of the means that can be used. In most cases, the filters used in water purification apparatus operate at constant pressure mode. viz. a filter is placed on a source of constant pressure and allowed to filter water until its rate of filtration is below some predetermined unacceptable value. In some cases, some degree of flow rate control is provided. For instance, U.S. Pat. No 5,503,735 discloses a liquid purification system which provides a reverse osmosis filter membrane in a filter cartridge. Not all of the water passes through the membrane and the water not passing through the membrane passes through a pressure relief valve which can be adjusted to vary the water pressure and flow rates in the system. Devices which maintain a constant flow rate and variable pressures are employed in the systems in which water flows, for instance, in irrigation systems. Processes for controlling the flow-through speed of the filter infiltration devices are also known. One such device is described in U.S. Pat. No. 5,238,559.
JP 06185070 (Kokai No. 5-185070) notes that in domestic water purifiers the filter module must be replaced when the water that has flown through it has exceeded the allowable absorption capacity of the absorbent inside the module, and that water purifiers are known which are provided with a life meter capable of displaying the time of replacing the filter module. However, the known devices are said to be unreliable because they measure only the time of the water flow and this does not provide a reliable indication due to fluctuations in the water flow rate. Therefore said application proposes a domestic water purifier which comprises a constant flow rate valve, a sensor for detecting start and stop of water flow and generating corresponding signals, and means for measuring an integrated operating time based on said signals and displaying a signal when said integrated time reaches a preset value. The application shows various structures of constant flow rate valves, but as to the filter module it shows no structure and states that the invention may utilize various structures of the prior art.
The filters used in water purification systems of the prior art, particularly those intended not merely to remove solid substances, but to remove microorganisms and render the water fully potable, are not fully satisfactory from several viewpoints. The throughput of the filters is usually low, so the filters must be changed frequently. The filters must have a large surface area. Since microporous membranes are required for the removal of microorganisms, such filters are very expensive.
It is a purpose of this invention to provide a filter device that is adapted for purifying water, and which is free of the defects of the existing devices.
It is another purpose of this invention to provide a filter element for making such a filter device.
It is a further purpose of this invention to provide a process for making such a filter element and filter device.
It is a still further purpose of this invention to provide a method for optimizing the operation of said filter device.
Other purposes and advantages of the invention will appear as the description proceeds.
SUMMARY OF THE INVENTION
The filter device according to the invention is composed of a number of component filter elements, although each filter element by itself would be capable of a filtering action. A filter element according to the invention comprises:
a)—an innermost drainage layer, preferably a substantially open, plastic netting;
b)—two layers of microporous membrane, preferably supported each on a support fabric layer disposed between it and said drainage layer; and more preferably, having a retentivity greater than 95% for microorganisms, said two layers being symmetrically disposed adjacent to the two sides of said drainage layer;
c)—two layers of a depth filter or prefilter (these two terms being used as synonyms in this specification), preferably a glass fiber filter, symmetrically disposed adjacent to the two outer sides of said microporous membrane layers;
d)—said microporous membrane layers and said depth filter layers being sealed together along a top edge, preferably extending above the top of said drainage layer and of said support fabric layers, if present;
e)—said drainage layer and said microporous membrane layers, as well as said support fabric layers, if present, extending at their bottom below the bottom of said depth filter layers, said microporous membrane layers being sealed to said depth filter layers at the bottom of these latter; and
f)—said microporous membrane layers and said depth filter layers being wider than said drainage layer, and said support fabric layers, if any, and being sealed together along their lateral edges.
The terms “top” and “bottom” refer to the position which the filter element will have in the complete filter device. Said filter device comprises a base plate having a central opening and an upper surface, and a plurality of elements as hereinbefore defined, arranged parallel to one another and perpendicular to said base plate, and traversing said central opening thereof with the bottom of their depth filter layers at the level of said base plate upper surface, said filter elements being potted to said base plate by filling with adhesive the space between them and the inner edge of said base plate's central opening. The said filter further comprises a sealed housing, in which the base plate with the filter elements potted thereto is enclosed in a tight manner.
In an embodiment of the invention, the microporous membrane layers and the depth filter or prefilter layers of the aforesaid filter element are sealed together by means of adhesive.
In other embodiment of the invention, the depth filter layers are laminates, each comprising a layer of porous thermoplastic fabric, and the microporous membrane layers and their support layers are thermoplastic. If the melting temperature of the microporous membrane layer is at least 50° C. higher than those of at least one of the remaining thermoplastic layers, the layers can be sealed together by the application of pressure and heat as better explained hereinafter.
The invention also provides a method of purifying water, provided that it not drinking water. The purification of water that is not fit for drinking, to render it potable, and the purification of potable water, to increase its purity—botrh purification being included in the expression “purifying drinking water”—are not comprised in this invention and are disclaimed herein. Said method comprises causing the water to flow at a constant flow rate through a purification filter comprising depth filter or prefilter and microporous membrane filter means, monitoring the time from the installation of the filter, monitoring the aggregate time during which the water is flowing through the filter, and preventing the flow of water through the filter when either of those times has reached a predetermined threshold value. The means for driving the water through the filter at a constant flow rate may comprise means for applying pressure to the filter and means for controlling the flow rate regardless of changes in the pressure drop across the filter, such as a flow restrictor of a known type. The depth filter means and microporous membrane means are preferably structu
Helfgott & Karas P.C.
Osmotek Ltd.
Savage Matthew O.
Ward Richard W.
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