Liquid purification or separation – With repair or assembling means – Sliding or rolling on guide means
Reexamination Certificate
2002-04-02
2003-11-04
Prince, Fred G. (Department: 1724)
Liquid purification or separation
With repair or assembling means
Sliding or rolling on guide means
C210S488000, C210S489000, C425S197000, C425S199000
Reexamination Certificate
active
06641728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Technical Field of the Invention
The present invention relates to a device for filtering a liquid, particularly for filtering a polymer plastic melt, having an inlet channel, a connecting channel, and a discharge channel.
2. Background Art
A device for filtering a polymer plastic melt is known from German Patent 195 19 907 C. The known device, which is referred to as a filter changing device in German Patent 195 19 907 C, has a housing which includes an inlet channel, a connecting channel arranged in a shaft and a discharge channel in that order, as seen in the flow direction of the liquid to be filtered. With the known filter changing device, the connecting channel is equipped with at least two filters arranged side by side and across the flow direction of the liquid in the connecting channel, the cylindrical shaft being mounted axially displaceable in a cylindrical bore in a liquid-tight manner accordingly. Through an axial displacement of the shaft, the two filters are moved between a filtration position, in which the inlet channel is connected to the discharge channel through the connecting channel, and an externally accessible cleaning position, in which the connection from the inlet channel to the discharge channel is interrupted and vice versa, so that both filters can optionally filter the liquid flow passing through them simultaneously either in the filtration position, which is also referred to as the working position in German Patent 195 19 907 C, or in the cleaning position. Through an axial displacement of the shaft, the filters with the known device can be brought into a position, which is referred to as the third filter changing position in German Patent 195 19 907 C, whereby in this position, the filter carrier assumes a position in which the filters are accessible from the outside, so that the filters can be replaced when they become soiled accordingly.
Due to the fact that with the known device, the two filters are situated with an axial distance between them as seen in the axial direction of displacement of the shaft, the known device requires a shaft designed to be relatively long axially in order to make available the required sealing face between the wall of the bore and the outside wall of the shaft.
To overcome this disadvantage of the relatively large axial length of the shaft and of the housing which cooperates with it, German Utility Model 295 19 140 U proposes that the filter be widened in the shape of an oval as seen in the direction of axial displacement of the shaft, so that with this known filter device accordingly, the two filters described above, which are situated side by side and with a distance between them are replaced by one single oval filter. However, German Utility Model 295 17 140 U explicitly points out that to avoid an irregular liquid flow, as seen over the surface of the filter, the known oval filter is provided with a special filter carrier plate which is situated downstream from the oval filter and supports the filter during the filtration process, whereby this filter carrier plate has longer channels in the central portion of the filter and shorter channels in the corner areas to equalize the flow.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a device for filtering a liquid, particularly a polymer plastic melt, which can be manufactured and operated especially inexpensively while retaining a compact design.
The device according to this invention for filtering a liquid, particularly for filtering a polymer plastic melt, has, also like the known devices described above, a housing which includes an inlet channel, a connecting channel arranged exclusively in a shaft and a discharge channel in that order, as seen in the flow direction of the liquid to be filtered. The connecting channel, which is delimited by the thickness of the shaft, has at least two filters arranged side by side and oriented across the flow direction of the liquid in the connecting channel, whereby the shaft, which is designed to be primarily cylindrical, is mounted so that it is liquid-tight and is axially displaceable in a bore of the housing fitted to it. Due to the axial displacement of the shaft with the device according to this invention, the two filters can be moved between a filtration position, in which the inlet channel is connected to the discharge channel through the connecting channel and the liquid flow is passed continuously through the connecting channel and thus also through the two filters, and a cleaning position, which is accessible from the outside and in which the connection of the inlet channel to the discharge channel is interrupted and the two filters can be removed from the connecting channel and cleaned or replaced accordingly. In contrast with the prior art, the connecting channel of the device according to this invention has a first area, which is situated directly upstream from the two filters arranged side by side, and which forms a single common liquid distribution space for the two filters, and a second area connected directly to the first area, as seen in the flow direction of the liquid to be filtered, whereby in the second area the two filters are situated side by side so that the two filters partially overlap. Both the first area and the second area of the connecting channel have a cross section perpendicular to the flow direction of the liquid to be filtered and thus as seen from above such that its shape corresponds to the shape of two overlapping circles.
In other words, the device according to this invention differs from the prior art essentially in that two circular filters are situated side by side and are arranged so that they overlap in a suitably shaped second area of the connecting channel, whereby a first area of the connecting channel also having overlapping circular cross sections upstream from these two filters, so that a single common liquid distribution space is formed for both filters in this way.
The device according to this invention has a number of advantages. Thus, it should be pointed out first that in contrast with the device known from German Patent 195 19 907 C, it has a much shorter overall length even with filters of an identical size, because in this way the space upstream from the filters is not designed as separately arranged individual bores running in parallel. Due to the compact arrangement of the two filters in an overlapping manner and side by side, it is possible with the inventive device to greatly reduce the required sealing area between the wall of the shaft and the inside surface of the bore supporting it, by accepting a slight reduction in the filter area, which depends on the degree of overlapping of the two filters; this results in a corresponding cost advantage in the production of the inventive device, because high demands are made regarding the precision of the shafts and the inside wall of the bore.
In comparison with the device known from German Utility Model 295 17 140 U, the inventive device can be produced much less expensively because, as explained above, the first and second areas of the connecting channel consist of two overlapping bores, whereas in the known device it is because of the oval design of the filter necessary, to produce these two areas, which are situated upstream from the oval filter, also as an oval connecting channel area, which necessitates additional machining steps. In addition, these oval filters to be used in the known device are specially manufactured parts which are many times more expensive in comparison with the filters used with the inventive device, so that considerable additional costs are incurred with any replacement of the filters, which may be necessary in a cycle of hours or days. A reason for a limited technical application of the known device may also be seen in the special design as an oval filter, because the plurality of filter finenesses offered with traditional round filters are not available for this design. In addition, because of the oval design of the filter, th
Greenberg Traurig P.C.
MAAG Pump Systems Textron GmbH
Prince Fred G.
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