Liquid purification or separation – Plural distinct separators – Filters
Reexamination Certificate
1997-04-29
2001-04-03
Savage, Matthew O. (Department: 1723)
Liquid purification or separation
Plural distinct separators
Filters
C210S349000, C210S436000, C210S450000, C210S455000
Reexamination Certificate
active
06210577
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention generally relates to the filtering of liquids and more specifically to the high-purity filtration of high temperature etching liquids, primarely used in the processing of semiconductor devices and requiring very high reliability at an extremely low particle count, and to the filtration of liquids in the pharmaceutical and chemical industries.
2. Description of the Prior Art
Presently available filter housing assemblies use cartridges inserted into a cylindrical housing with a twist-screwtop to tighten an O-Ring against the housing flange for generating a sealed unit with an inlet and an outlet for the liquid to be filtered. The liquid enters under pressure through the inlet into the space between the housing and the cylindrical filter cartridge and is forced radially inward through the filter. The filter surrounds a concentric cylindrical space through which the filtered liquid exits from the outlet at the bottom of the filter housing. The filter cartridge is closed off at its top and has a nose at its bottom, surrounded by O-rings, by which the cartridge is held in the bottom recess of the filter housing. Potential shortcomings of the filter housing are damage to the O-ring because of twisting, deforming and abrasive action during screw-on closure, which can contribute to leakage and a decrease in filtration efficiency. Usually the cartridge is inserted and held only at the housing bottom by two parallel O-rings around the cartridge nose. The filter cartridge may tilt as a consequence of fluid pressure action and no longer be concentric with the filter housing, causing an uneven flow through the cartridge. This action also may contribute to lower filtration efficiency and a higher particle count by uneven filtration or by bypassing of the filter as well as to lower filter cartidge life. Together with the used cartridge filter housings are often thrown away, amounting to economical and environmental waste. Where ultrapure filtration is needed, several filters, possibly with decreasing particle size, may be used, requiring several filter housings in sequence at an increased cost. Molded orifices at the top portion of the housing have been used to relieve over-pressure or for back-flushing.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a housing assembly design for at least two filters in series, made out of a suitable plastic like “TEFLON”®, for the prevention of leaks, even at temperatures in the range of 190 degrees Celsius (375 degrees F) and at pressures as high as 5 bars (70 psi), for even flow characteristics throughout the life of the filter cartridge and for creating an extremely low particle count. The filter housing can hold several cartridges in sequence, directing the liquid to be filtered through proessively finer filters, which are usually also progressively more expensive. The coarse, cheaper filter clogs up faster and will have to be changed more often, while the finest filter would have the longest operating life. Often it is more economical to replace the cartridges together to minimize downtime. A filter cartridge change in the equipment described is easily done by removing only the top housing without disconnecting inlet and outlet pipes, minimizing equipment downtime.
Briefly, a preferred embodiment of the present invention includes a bottom housing, a tube-shaped extension housing, for holding at least one cartridge, and a top housing. The respective lower and upper ends of the interfaces between housings have a similar structure. The upper ends have a lip around the opening carrying an outside thread for receiving the inside thread of a nut ring pushing against a flange around the lower ends of matching lower inter-face ends for fastening. The lower and upper ends of these cartridges are held concentric by adapter rings and flow-through spacer rings. An adapter ring centers the nose of an upper cartridge and directs the liquid flow from the nose of an upper cartridge to the cylindrical outer surface of a lower cartridge for an inwardly radial flow across the filter and downward through the nose while sealing against the pressure drop across the cartridge. An upper and a lower cartridge can be joined for easy insertion and removal through the top of the housing without requiring the disassembly of the inlet and outlet pipes. The top housing also contains an opening in its top for the insertion of a vent tube with a very small cross-section, which enforces a certain liquid level in the housing to generate an air space on top of the upper cartridge. This air pocket, the lower end of which is defined by the lower end of the vent tube, serves as a damper for pressure variations generated by the pump feeding the filter housing assembly. The cross-section of the vent is very small compared to the filter area resulting in a very small leakage volume which is fed back to the intake of the pump feeding the filter. The adapter ring is a crucial element in connecting several cartridges in series for easy insertion and removal in order to minimize downtime during operations. From its recess it carries a downward tube carrying flow-through holes at its lower end such that above these holes and below the adapter ring air pockets can be sustained which are in series with the air pocket at the top of the housing assembly, thus providing a multi-dampening effect on pressure variations due to pump action.
An advantage of the present invention is that the interfaces are joined by a sliding action, avoiding a twisting and abrasive action on the O-Rings that provide a seal between the housings.
Another advantage of the present invention is the provision of a quadruple seal between housings by using semicircular grooves in opposing surfaces between housings for the accommodation of sealing O-rings.
Another advantage of the present invention is the provision of a circular spacer around the top of the filter cartridge asserting its concentric positioning, thus providing an even liquid flow through the filter and preventing tilting of a cartridge and damage to the cartridge nose O-rings.
Another advantage of the present invention is the easy and fast insertion and removal of cartridges through the top of the housing without disconnecting inlet and outlet pipes thus minimizing equipment downtime.
Another advantage of the present invention is the formation of an air space above the level of the liquid, defined by the lower end of a vent tube through the cap for the dampening of pressure variations generated by the pump feeding the filter and for maintenance of a minimum liquid level around the filter cartridge, thus contributing to an efficient filtration and a low particle count.
Another advantage of the present invention is the easy adaptation of the housing for the use of as many filter cartridges as needed and the easy change of cartridges.
Another advantage of the present invention is the easy adaptation of a modified version of a multi-cartridge assembly to a one-piece molded assembly for easy insertion and removal for minimizing downtime during operations.
REFERENCES:
patent: 3870636 (1975-03-01), Schettler
patent: 5089131 (1992-02-01), Gentry
patent: 5158585 (1992-10-01), Saho et al.
patent: 5609757 (1997-03-01), Schiavo et al.
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