Liquid purification or separation – Casing divided by membrane into sections having inlet – Each section having inlet
Reexamination Certificate
1999-09-27
2001-03-27
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Casing divided by membrane into sections having inlet
Each section having inlet
C210S416100, C210S416300, C222S189060, C222S200000, C222S336000, C222S189090, C222S189110, C422S105000
Reexamination Certificate
active
06207052
ABSTRACT:
TECHNICAL FIELD
The invention relates to microfiltration devices which use hydrophillic membranes to sterilize liquids, and more particularly to a method and apparatus for removing air locks which develop on the upstream side of the filter membrane within these apparatus.
BACKGROUND ART
Microfiltration is a commonly used for sterilizing liquids and gases. See for example the present inventor's device disclosed in International application no. PCT/CA91/00056, published Mar. 19, 1992 under no. WO 92/04004. In that device, a liquid sterilizing micro-filter is mounted on the outlet of a storage container to dispense sterile saline. A plunger is used to draw saline up from the container and force it through the microfilter, thereby sterilizing and dispensing the saline. A second micro-filter sterilizes the air which is drawn into the device to replace the ejected saline. Other prior art devices which employ hydrophillic membrane filters to sterilize liquids include those shown in applications no. GB 1,000,248; GB 2,106,877; and U.S. Pat. Nos. 4,938,389 and 4,533,068.
Within the microfiltration industry it is known that the integrity of a wetted microfilter membrane and its accompanying seals can be tested by pressurizing the upstream surface of the filter with air. The presence of air bubbles on the downstream side of the filter at relatively low air pressure indicates the presence of a leak either around the filter or through a defect within the membrane itself. The air pressure can be increased to a point where air is able to penetrate through the pores of the membrane. This is called the “bubble-point” test. It can be used to verify the pore size of the filter membrane, however, air-borne micro-organisms may also pass through the filter along with the air.
Once an integrity test has been conducted, the air on the upstream side of the filter remains trapped. This air could be pushed through the filter with liquid at pressures that exceed the “bubble point” pressure, but this may not be desirable for hand held filtering devices that are intended to deliver multiple unit doses of sterile liquid. The trapped air could also be removed from the upstream surface of the filter by inverting the entire device and allowing gravity to temporarily displace the air. This method may be valid but does entail certain technical disadvantages.
There is therefore a need for a mechanism that is capable of introducing and then removing air from the upstream surface of a hydrophillic filter membrane within a manually operated filtration device so that the operator may assure himself that the filter within the device if fully functional, without leaving an air lock on the filter.
DISCLOSURE OF INVENTION
The present invention provides a method and apparatus for removing an air lock from the upstream side of a microfilter in a device for dispensing a sterile liquid from a storage container by forcing the liquid through a microfilter, the device comprising a first inlet passageway communicating between the storage container and a chamber on the upstream side of the filter closable by a first valve, a second outlet passageway communicating between the storage container and the chamber on the upstream side of the filter closable by a second valve, the method comprising the steps of:
a) creating a partial vacuum in the chamber upstream of the microfilter to thereby open the first valve and draw the liquid from the storage container through the first passageway into the chamber and into contact with the upstream side of the filter;
b) closing the first and second valves and increasing the air pressure in the upstream chamber; and
c) opening the second valve thereby releasing air under pressure from the upstream chamber through the second passageway.
REFERENCES:
patent: 4463880 (1984-08-01), Kramer et al.
patent: 4533068 (1985-08-01), Meierhoefer
patent: 4714550 (1987-12-01), Malson et al.
patent: 4938389 (1990-07-01), Rossi et al.
patent: 4940542 (1990-07-01), Simizu et al.
patent: 5120438 (1992-06-01), Nakagawa et al.
patent: 5130015 (1992-07-01), Simizu et al.
patent: 5785858 (1998-07-01), Webb
patent: 6019899 (2000-01-01), Webb
WO 92/04004 (Webb) Mar. 19, 1992.
Fortuna Ana
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
Webb Garth T.
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