Pipe joints or couplings – Packed – Screw thimble
Reexamination Certificate
1999-02-25
2001-02-27
Browne, Lynne H. (Department: 3629)
Pipe joints or couplings
Packed
Screw thimble
C285S353000, C285S343000
Reexamination Certificate
active
06193286
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to fittings and, more specifically, to devices and methods for connecting fluid conduits (e.g., tubes) to receiving fittings. This invention is particularly applicable to the field of chromatography.
BACKGROUND OF THE INVENTION
A variety of tube fittings that are useful in the field of chromatography are commercially available. Most of these fittings employ a ferrule system that is swaged onto the tube.
One known design for making what is referred to as a “low dead volume connection” is called a “slip-free connector”. With this connector, the depth of tubing penetration into a receiving fitting, and the compression force on a polymeric sealing ferrule, can be independently adjusted through the use of a two-part nut. The design of this connector is described as part of a chromatographic cartridge in U.S. Pat. No. 5,582,723. Unfortunately, this design can be difficult to use if the back part of the nut is too tight prior to installation into a receiving fitting. When this occurs, the tubing bottoms out in the receiving fitting and prevents compression of the sealing ferrule. Continued tightening of the “slip-free connector” without first loosening the back part of the nut eventually causes damage to the tubing or the receiving fitting.
A problem with tubing connection fittings in general is interchangeability from manufacturer to manufacturer. Different manufacturers use different penetration depths from the end of the sealing ferrule to the bottom of the receiving fitting, and penetration depths can even vary among different products from the same manufacturer. Because these fittings are assembled with the ferrule permanently swaged onto the tubing, using an already assembled tube in a different fitting can cause problems. If the tube extends too far past the end of the swaged-on ferrule the tube will bottom out in the fitting, which can make it difficult to get an adequate seal, or can damage the fitting. Conversely, if the tube does not extend far enough beyond the swaged-on ferrule the space not filled by the tubing results in dead volume. Use of the “slip-free connector” described above addresses the problem with interchangeability of fittings from one manufacturer to another, but as described above it can be difficult to use.
It is generally difficult to obtain reliable seals on {fraction (1/32)}&Dgr; tubing, which is common in chromatography applications. This size of tubing is typically thin-walled and, as the ferrule is tightened, the tubing can be deformed to the point where a reliable seal cannot be achieved. Continued tightening only aggravates this problem, and eventually the tubing is crimped closed or the sealing nut breaks.
U.S. Pat. No. 4,669,756 describes the use of a spring-loaded fitting to controllably force the ends of soft plastic tubing together to make a seal. In this case the ferrules are attached to the tubing ends and then pressed together with a spring. This is claimed to work with soft tubing, where deformation of the tubing ends occurs as they form the seal. As a result, this device has limited capability to seal to high pressure.
In addition, U.S. Pat. No. 4,732,672 describes a means of quickly mounting high-pressure liquid chromatography columns by using spring tension to force tubing into the end fittings of the columns. This same spring tension produces force on the sealing ferrule as well. The device is large and cumbersome, however, and the force on the tubing is achieved by a tight bend through a channel to a perpendicular dimension. Thin-walled tubing would collapse under forces required to keep it from being pushed out of the end fitting during high-pressure use. Also, the fact that the same spring is used to provide the tube holding force and the ferrule compression force means there is no independent control of these parameters.
U.S. Pat. Nos. 4,991,883, 5,163,722, and 5,163,215 describe spring-loaded connection devices wherein controlled pressure is applied to the sealing ferrule. This provides a constant sealing force on the ferrule member but does not provide for automatic bottoming out of the tubing in the receiving fitting.
U.S. Pat. Nos. 5,188,730 and 5,525,303 describe multiple-part connection devices that provide for dead volume removal by adjustment of a tubing member. These are similar to the “slip-free connection” device described earlier, and they suffer from the same problems, namely, that the rear supporting threaded member can be prematurely tightened, causing the tubing to prematurely bottom in the receiving fitting. This causes unreliable sealing and potential damage to the tubing or the receiving fitting.
The failure of current connection fittings to provide a reliable means of sealing tubing in a receiving fitting while automatically removing dead volume shows the need for a fitting that provides a simple, convenient yet robust means of connecting tubing to a receiving fitting while automatically removing dead volume in a small easy to use package.
SUMMARY OF THE INVENTION
A device in accordance with this invention connects a fluid conduit, such as a tube, to a threaded receiving fitting. The device includes a retention member (e.g., a washer) that attaches to the fluid conduit, and a fitting member that has a first threaded end that connects to the threaded receiving fitting and a second, opposing threaded end with a substantially axial cavity. The first threaded end has a substantially axial hole extending through to the cavity in the second threaded end that receives the fluid conduit so the conduit extends through the cavity and hole with the retention member proximate an interior end of the cavity and an end of the fluid conduit extending beyond the first threaded end. A deformable member (e.g., a sealing ferrule) seals the connection to the receiving fitting. The deformable member has a substantially axial hole through it that receives the fluid conduit so that the deformable member abuts the first threaded end of the fitting member and the end of the fluid conduit extends beyond the deformable member into the receiving fitting. A bias member (e.g., a spring) is coaxially mounted on the fluid conduit with a first end of the bias member abutting the retention member in the cavity in the second threaded end of the fitting member. A cap member has a threaded cavity that connects to the second threaded end of the fitting member so that a second end of the bias member abuts an interior end of the threaded cavity. The cap member also has a substantially axial hole through it that receives the fluid conduit.
In another embodiment of this invention, a fluid conduit is connected to a receiving fitting by positioning a deformable member coaxially about the fluid conduit. The fluid conduit is then biased against the receiving fitting and, independent of the act of biasing the fluid conduit, the deformable member is driven into the receiving fitting to seal the fitting.
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Jones Brian A.
Kelly Curtis
Porter Nathan L.
Browne Lynne H.
Dunwoody Aaron
Holland & Hart LLP
Selerity Technologies Inc.
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