Liquid chromatography systems generally consist of a number of separate components. These components are connected to each other with tubing, preferably flexible tubing. A fitting is generally required to secure the tubing to each individual component. A common fitting consists of a plastic housing with a shaft therethrough.

The housing has a threaded portion at one end that secures to the liquid chromatography component and the tubing runs through the shaft and to the component. A problem is encountered when it is necessary for a technician working with liquid chromatography equipment to disconnect the tubing from the component to work on the system. When the tubing is disconnected, the fitting is free to slip and slide along the tubing. As a result, two problems can occur. First, the fitting may fall off of the tubing onto the floor and be contaminated or lost. Second, the fitting may slide along the tubing towards another component and frustrate the user.

One solution to this problem is incorporated in a fitting manufactured and sold by Alltech Associates, Inc. of Deerfield, Illinois. This fitting incorporates an O-ring in the receiving end of the shaft. The O-ring is disposed in the shaft and has an inner- diameter that is smaller than the outer diameter of the tubing and the inner diameter of the shaft. When the tubing is inserted in the shaft, and through the 0-ring, the smaller diameter O-ring grips the tubing and secures the fitting to the tubing. This design prevents the fitting from slipping off the tubing; however, it has three possible disadvantages. First, this design complicates the manufacturing process. The 0-ring must be separately manufactured and installed in the fitting. This adds to the expense and complexity of manufacturing the fitting. As a result, the end product is more expensive and can be prone to statistically unavoidable manufacturing flaws. Second, the O-ring is typically a different material than the fitting. Unlike the hard material of the fitting, the O-ring must be softer in order to resiliently and flexibly engage the tubing that passes therethrough. This softer O-ring material is typically less resistant to chemical and heat degradation than the fitting and, thus, subject to failure if laboratory solvents are spilled on it or other extreme conditions are encountered. Last, the 0-ring, because it is a separate component of the fitting, is capable of being removed from the fitting. If the O-ring is removed, either on purpose or inadvertently, the fitting is once again free to slide along, and fall off, the tubing.

SUMMARY OF THE INVENTION A fitting is provided that comprises a shaft. The shaft has an inner peripheral surface, a connecting end and a receiving end. At least one projection is located on the inner peripheral surface of the shaft. Preferably, the shaft has a plurality of diameters between the connecting end and the receiving end and the diameter of the shaft at the location of the projection (s) is less than the diameter of the shaft at any other point between the connecting end and the receiving end.

Also provided is a fitting that comprises a ferrule and a head. The ferrule and head each have a shaft with an inner peripheral surface. At least one of the shafts includes at least one projection. The projection is located on the inner peripheral surface of the shaft.

Also provided is a method of using a fitting having at least one projection in a liquid chromatography system.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of a preferred fitting in the preferred environment of the present invention; Fig. 2 is a cut-away perspective view of a preferred fitting of the present invention; Fig. 3 is a cross-section of a preferred fitting of the present invention; and Fig. 4 is an end view of a preferred fitting of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In its most general sense, the present invention consists of a hollow fitting.

Within the hollow portion of the fitting, the shaft, is at least one projection.-The projection decreases the effective diameter of the hollow portion to less than the outer diameter of tubing that passes through the fitting. As a result, the projection frictionally engages the tubing and prevents uncontrolled slippage of the fitting off of the end of the tubing.

The fitting of the present invention may be used in any application in which a fitting is used with tubing. The most preferred embodiment is in a liquid chromatography system ; specifically, to secure tubing to the components of a liquid chromatography system, or to secure separate lengths of tubing to each other. The tubing may be constructed of any material and the type of material does not limit the scope of the present invention. The most preferred material is poly ether ether ketone (PEEK). The tubing may also be constructed from carbon reinforced PEEK, stainless steel, nylon, DELRINs, silicone rubber, polypropylene, polyethylene, TEFZELe, KEL-Fe, and/or polytetrafluroethylene (TEFLONe). The fitting of the present invention may be used in liquid chromatography systems, or in conjunction with liquid chromatography components. Such liquid chromatography systems or components are manufactured by such companies as Alltech Associates, Beckman, Parker, Swagelok, Rheodyne, Upchurch, Valco and Waters. The general method for using the fittings of the present invention in a liquid chromatography system is shown and described in U. S. Pat. No 4,586,733 to Anderson which is hereby incorporated by reference in its entirety.

The preferred embodiments of the fitting 10 of the present invention will be described with reference to Figs. 1-4. Generally, the fitting of the present invention includes a head 11 and a ferrule 12. Preferably, the head 11 and ferrule 12 are of unitary construction, as shown in Figs. 1-4; however, the head and the ferrule may also be separate components as will be described below. The head 11 preferably contains a threaded portion 13 that secures the fitting 10 to a component 14 and a knurled portion 15 that facilitates tightening of the threaded portion 13 into the component. The ferrule 12 has a tapered outside diameter 16 and fits into a corresponding port in the component 14. A shaft 17 passes through the head 11 and the ferrule 12.

The shaft 17 is defined by an inner peripheral surface 18 of the fitting 10. The shaft 17 accepts the tubing 19. Typically, the tubing 19 is inserted into the fitting 10 at the end of the fitting 10 with the head 11. This is the receiving end 20. The tubing 19 typically exits the fitting 10 at the end of the fitting 10 with the ferrule 12. This is the connecting end 21. The shaft 17 has an axial distance between the receiving end 20 and the connecting end 21. The shaft 17 is preferably cylindrical (i. e., circular cross section); however, the dimensions or shape of the shaft 17 do not limit the scope of this invention. The shaft 17 may alternatively be square, rectangular, elliptical, triangular or trapezoidal in cross-section. In addition, the shaft 17 does not have to be a continuous shape for its entire length. For example, in the preferred embodiment of Figs. 2 and 3, the shaft 17 has a greater inner circumference and diameter at the receiving end 20 than at the connecting end 21.

Disposed on the inner peripheral surface 18 of the shaft is at least one projection 22. Preferably, as shown in Fig. 4, there are multiple projections, most preferably, three. In a preferred embodiment, Fig. 4, the projections 22 are equally spaced along a circumference that is perpendicular to the axial distance. Alternatively, the projections 22 may be randomly spaced on the inner peripheral surface 18, staggered on each side of a circumference of the shaft or equally spaced along a circumference that is not perpendicular to the axial distance.

The projections 22 have a shape and location that narrows the diameter of the shaft 17 at the location of the projection 22. The term"diameter"is used because the preferred shape of the shaft is circular; however, it is understood that"diameter"also applies to any shape shaft 17 and"diameter"means the diameter of the largest circle that will fit in a shaft 17 at a particular point.

The shape of the projection 22 may be any shape that serves to limit the diameter of the shaft 17 so as to facilitate retention of the fitting 10 on the tubing 19. In the preferred embodiment, as shown in Fig. 2, the projections are semi-conical shaped.

That is, they are shaped like a cone that has been halved along the vertical axis.

Preferably, the narrow end of the cone faces the receiving end 20, as shown in Fig. 2.

Alternatively, the projections 22 may be semi-spherical, pyramidal, semi-cylindrical, or a random shape.

The projections may be located at any point on the inner peripheral surface 18 of the shaft 17 that facilitates retention of the fitting 10 on the tubing 19. Preferably, the projections 22 are located in the ferrule portion 12 of the fitting. This location is preferred because it makes formation of the projection 22 easier during the manufacturing process, as discussed below.

A threaded portion 13 is preferably used to secure the fitting 10 to the component 14 into which the tubing 19 is being inserted or attached. The threaded portion 13 may alternatively be any other means of securing the fitting to a component, such as a luer taper, spring loaded quick disconnect, or a friction fit.

The head 11 of the fitting 10 preferably includes a mechanism to facilitate gripping and rotation of the fitting 10. Preferably, the head 11 includes knurls 15 to allow a user to tighten the fitting 10 to the component 14 by hand. Alternatively, the head 11 may include a standard hex nut design (not shown) so that a wrench may be used to tighten the fitting 10 to the component 14.

Instead of the unitary design of Fig. 1-4, the fitting of the present invention may also consist of separate head and ferrule components. In this alternative embodiment, the head 11 and ferrule 12 are separable components wherein the ferrule 12 preferably has a tapered end that may be inserted into the shaft of the head 11.

The fittings of the present invention may be constructed of any material that is capable of securing tubing to a component. Preferably, the material is resistant to laboratory chemicals. Accordingly, preferred materials are polymer resins. The most preferred material is poly ether ether ketone (PEEK) ; however, other suitable materials are carbon reinforced PEEK, stainless steel, nylon, DELRIN, polypropylene, polyethylene, TEFZELe, KEL-Fe, polytetrafluroethylene (TEFLONe). In addition, the fittings need not be constructed of a single material. For example, the head may be constructed of stainless steel, and the ferrule may be constructed of PEEK, or vice versa.

The fitting of the present invention may be manufactured according to any known method of working with the constituent materials. The most preferred method of manufacture is injection molding; however, the fitting may also be manufactured by compression molding or hand machine. Injection molding is preferred because it facilitates the molding of the projections. This is because the projections may be located on the inner peripheral surface at the point that corresponds to where the ferrule meets the threaded portion. It is possible to construct the injection mold such that the seam of the mold, and the indentations for the projections, corresponds to this point so as to easily form the projections.

Of course, it should be understood that a wide range of changes and modifications can be made to the embodiments described above and depicted in the drawings. It is intended, therefore, that the foregoing description illustrates rather than limits this invention, and that it is the following claims, including all equivalents, that define this invention.