This invention relates to a spiral wound filtration cartridge construction utilized in fluid separation processes such as reverse osmosis or ultrafiltration. More particularly, this invention relates to a spiral wound filtration cartridge construction having a chevron seal construction with a partial feed bypass means which prevents fluid stagnation within and around the cartridge during use.
Prior to the present invention, spiral wound filtration cartridges have been provided comprising a centrally positioned tube about which are wound membrane sheets and suitable permeate spacers and feed spacers. The membrane sheets are V shaped and the feed spacers are positioned within the shaped membrane while the permeate spacers are positioned outside the V shaped membranes. The feed spacers promote passage of feed fluid into the V shaped membrane and the permeate spacers promote permeate flow from outside the V shaped membrane into holes through the walls of the centrally positioned conduit for recovery. The feed passes axially through the spiral wound membrane cartridge and retentate is recovered from the opposite end at which the feed is introduced. The filtration cartridge is held within a cylindrically shaped housing to provide mechanical strength to the cartridge during use.
It has been proposed to provide a controlled by pass of feed fluid within the space between the housing and the outside surface of the cartridge in order to prevent bacterial growth during use caused by clogging of the cartridge with retentate. U.S. Pat. No. 4,301,013 discloses the use of a tight fitting open mesh within the housing space between the cartridge and the housing to provide the desired by-pass flow. It has also been proposed in U.S. Pat. No. 4,548,714 to wrap the cartridge with a leaf of the feed spacer to provide for fluid flow around the cartridge. It has also been proposed by U.S. Pat. No. 4,906,372 to utilize a seamless porous rigid sleeve within the housing to separate the cartridge from the housing and to provide for feed by-pass. These cartridges are difficult to produce with the requisite tolerance needed to permit their use in the field, particularly when it is desired to change the cartridge within the housing. That is, these cartridge and housing arrangements are difficult to replace in the field since each cartridge-housing arrangement varies in size and shape.
It has also been proposed in U.S. Pat. No. 5,128,037 to provide a filtration cartridge construction having a spiral wound filtration cartridge positioned within a cylindrical tube which, in turn, is positioned within a cylindrical housing. The space between the tube and the housing is sealed by a chevron shaped flexible seal secured to an end plate which is fixed to the cylindrical tube. Holes are provided in the end plate to permit fluid flow between the cylindrical tube and the housing thereby to prevent bacterial growth in the space between the tube and the housing. This use of the end plate to secure the chevron seal is undesirable since the end plate is expensive and sealing is usually effected by ultrasonic welding which is time consuming and requires expensive apparatus. Alternatively, an adhesive or potting compound can be utilized to secure the chevron seal. However, this is undesirable since they can be a source of undesirable extractables that can mix with the permeate.
Accordingly, it would be desirable to provide a filtration cartridge construction which affords a controlled feed by-pass means to maintain the construction clean during use. It also would be desirable to provide a filtration cartridge construction which can be easily utilized in the field to permit cartridge replacement when needed. It would also be desirable to provide such a construction wherein the required seal can be properly positioned without the need for an end cap or adhesives.