Liquid purification or separation – Flow – fluid pressure or material level – responsive – Check valve
Reexamination Certificate
1999-04-29
2001-03-13
Savage, Matthew O. (Department: 1723)
Liquid purification or separation
Flow, fluid pressure or material level, responsive
Check valve
C210S194000, C210S323200, C210S333010, C210S355000, C210S411000, C210S413000, C210S415000
Reexamination Certificate
active
06200467
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a filtering device and, more particularly, to a filtering device suitable for use for precision filtering in a state submerged in liquid to be filtered. Liquid to be filtered includes water for general uses, drinking water, river water, pool water and chemicals.
Known in the art of filtering device is one which employs a plurality of filter tubes. In this filtering device, a plurality of filter tubes are provided in parallel in a container. Liquid to be filtered is introduced from an inlet provided in one end portion of the container via a pump and filtered through these filter tubes and filtered liquid, i.e., liquid which has passed through the filter tubes, is delivered out of a filtered liquid outlet provided in the other end portion of the container.
For the filter tubes used in the prior art filtering device, filter elements for precision filtering which consists of a porous material or a filtering cloth having densely formed pores are used. In these filtering cloth having densely formed pores of these filter elements, however, pores of these filter elements are blocked by fine powdery materials suspending in the liquid to be filtered in a relatively short period of time after starting of operation of the filtering device with the result that filtering efficiency is rapidly dropped. For this reason, the filtering operation of the filtering device has to be stopped for performing backwashing of the surface of the filter elements and resumed after removing the materials which have blocked the pores of the filter elements.
Backwashing has conventionally been made by supplying pressurized backwash water from an outlet of filtered liquid of a container into a filter tube to remove solids blocking pores of a filter element which constitutes the filter tube.
In the conventional backwashing method, it frequently occurs that when solids have been first dislodged from a part of pores which have been blocked and the part of pores are thereby opened, the backwash water injects from the part of pores which have been opened and the pressure of the backwash water applied to the other pores which have not been opened yet thereby is reduced with the result that the backwashing operation is finished while these pores remain blocked with solids. Accordingly, even if backwashing is repeated periodically, blocking of the filter element increases gradually until at last it becomes necessary to replace the entire filter element and this significantly reduces the efficiency of the filtering device.
It is, therefore, a primary object of the invention to provide a filtering device having an improved backwashing device capable of effectively preventing blocking of a filter element.
Since a filter element of the conventional filtering device causes blocking in a relatively short period of time, stopping of the filtering operation and performing of backwashing must be made frequently with resulting decrease in the filtering efficiency.
It is, therefore, another object of the invention to provide a filtering device which can significantly reduce frequency of stopping of the filtering operation and performing of backwashing in combination with the above described improved backwashing device.
SUMMARY OF THE INVENTION
For achieving the above described primary objects of the invention, there is provided a filtering device comprising a cylindrical screen, backwash tube made of a tubular member provided in said cylindrical screen coaxially with said cylindrical screen and rotatable about its axis, having an inlet for introducing filtered liquid in one end portion thereof and an opening for discharging filtered liquid and introducing backwash water in the other end portion thereof and having a plurality of backwash water injection holes formed along said backwash tube in an axial direction thereof at a predetermined interval, a liquid transfer tube communicating with said opening for receiving filtered liquid from said backwash tube and for introducing backwash water to said backwash tube, a check valve disposed within said backwash tube adjacent said inlet such that in a filtration operation filtered liquid is allowed to flow from said inlet into said backwash and liquid transfer tubes, and in a backwash operation backwash water is prohibited from flowing to said inlet from said backwash tube, and a backwash tube rotation means for rotating said backwash tube about its axis.
According to the invention, by injecting backwash water under pressure from the backwash water injection holes formed at a predetermined interval in the axial direction while rotating the backwash tube about its axis in the cylindrical screen, the backwash water is injected in a jet stream under a concentrated large pressure and this jet stream of backwash water sequentially collides with the entire inner periphery of the cylindrical screen as the backwash tube is rotated whereby blocking of the cylindrical screen is removed uniformly over the entire inner periphery of the cylindrical screen.
In one aspect of the invention, said backwash tube rotation means is a blade mounted on an inner surface of the backwash tube. According to this aspect of the invention, when the backwash water under pressure is introduced into the backwash tube, the flow of the backwash water pushes the blade and the backwash tube thereby is rotated. Therefore, for rotating the backwash tube, another drive unit including an electric motor and an electrical driving circuit is unnecessary so that the filtering device can be constructed in a compact design at a minimum cost.
In another aspect of the invention, said backwash tube rotation means consists of the backwash water injection holes of the backwash tube which are formed at an angle to radial direction of the backwash tube in a horizontal plane. According to this aspect of the invention, when the backwash water under pressure is introduced into the backwash tube, the backwash water stream which is injected from the injection holes which are offset from the radial direction of the backwash tube collides with the inner wall surface of the cylindrical screen in the form of an offset flow and the backwash tube thereby is rotated in one direction. Therefore, as in the structure including the blade mounted on the backwash tube, no other drive device is required for rotating the backwash tube.
For achieving the above described second object of the invention, there is provided a filtering device which further comprises a filter container in which one or more of said cylindrical screens are housed, said filter container comprising an inlet for the liquid to be filtered, an outlet for the liquid to be filtered, a liquid transfer opening communicating with said liquid transfer tube and a drain outlet, said inlet for the liquid to be filtered having a larger diameter than the liquid transfer opening, and a pump connected between said inlet for the liquid to be filtered and said outlet for the liquid to be filtered to form a closed circuit between said inlet and outlet for the liquid to be filtered, said pump acting to compulsorily introduce, from said inlet for the liquid to be filtered, the liquid to be filtered of a larger amount than an amount of the filtered liquid which can flow out of said liquid transfer opening thereby to create, in said filter container, a flow of the liquid to be filtered having a direction which is different from direction of a flow of the liquid to be filtered into the cylindrical screen.
According to the invention, there is created a flow of the liquid to be filtered having a direction which is different from direction of a flow of the liquid to be filtered into the cylindrical screen. Powdery solids causing blocking of the screen suspending in the liquid to be filtered are washed away from the surface of the cylindrical screen by the flow having the different direction from the direction of the flow into the cylindrical screen and an amount of the powdery solids which enter the slits of the cylindrical screen is reducedd. The speed of blo
Cecil Terry K.
Hedman & Costigan ,P.C.
Savage Matthew O.
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