Patent Application
20120049512
Plastic tubing and fitting assemblies are used in many applications to transfer fluid, including for example pharmaceutical, chemical, semiconductor fabrication, to name a few. Fitting assemblies can be used to connect one tubing to another, or to connect tubing to a manifold or a utilization apparatus. Under high fluid pressure, the fitting assemblies may be susceptible to leakage.
Features and advantages of the disclosure will readily be appreciated by persons skilled in the art from the following detailed description when read in conjunction with the drawing wherein:
In the following detailed description and in the several figures of the drawing, like elements are identified with like reference numerals. The figures are not to scale, and relative feature sizes may be exaggerated for illustrative purposes.
The assembly further includes a cap member 70, which in this embodiment takes the form of a threaded nut, so that the cap member or nut can be threaded onto the body member 60 to secure it in place. The nut 70 includes a closed end portion 72 having a central opening 72A defined therein, an intermediate portion 74 having a cylindrical hollow configuration an interior surface 74A defining a cavity 78, and a distal portion 76 having interior threads 76A defined therein and configured to threadingly engage the exterior threads 64A-1 on the fitting body 60. The intermediate portion 74 has a diameter D4. The cavity is configured to fit about the flared end portion of the tubing and the tubing receiving portion of the fitting body 60, with a sleeve 100 fitted about the flared end portion in an interference fit. In other embodiments in which the function provided by the cavity is separated from the securing function of a nut, the cap member need not include threads. Two such embodiments are described below with respect to
In an exemplary embodiment, the fitting 60 and cap member 70 are each fabricated of a rigid plastic material, e.g. by injection molding, such as PFA or PVDF (both high purity materials to prevent liquid contamination due to tubing or fitting contamination) Other materials can be selected, based on the demands of the particular application.
The fitting assembly further includes plastic tubing member 80 including cylindrical tubing portion 82 having a first diameter D1, which in an exemplary embodiment is nominally the same as the diameter D2 of the fitting space 66. The tubing includes a flared end portion 84 having a slightly larger diameter D3 than diameter D1, and is configured to be fitted over the tubing receiving portion 64B of the fitting 60. In an exemplary embodiment, the tubing is flexible, and fabricated from a plastic material, e.g. a fluoropolymer, for high purity applications such as pharmaceutical and semiconductor fabrication applications. For one exemplary application, the inner diameter D1 of the tubing is 0.375 inch, and the inner diameter D3 of the flared end portion is 0.375 inch. The nominal thickness of the tubing in portion 82 is 1/16 inch in this example, and may be reduced in the flared region as a result of the flaring process used to fabricate the tubing.
The fitting assembly 50 further includes a sleeve member 100, configured for fitting over the end portion 84 of the tubing 80 and inside the intermediate portion 74 of the nut when assembled to the fitting and tubing. The sleeve may be made of any fluoropolymer resin, such PFV, PVDF, PEEK, HALAR™ which provides a flexibility or resilience property of the sleeve. Since the sleeve does not come into contact with the liquid being carried through the tubing and fitting, in a typical application it may be fabricated from a material not deemed a high purity material. In an exemplary embodiment, the sleeve outer diameter (OD) D6 (
The fitting nose portion 64B, the flared end portion 84, the sleeve 100 and the cavity wall surface 74 cooperate, with the fitting assembly in an assembled condition as shown in
Exemplary nominal diameter dimensions for one application are D1=0.375 inch, D2=0.375 inch, D3 (flared tubing ID)=0.545 inch, D3 (fitting nose OD)=0.55 inch, D4=0.7 inch, D5 (wall thickness of sleeve)=0.021 to 0.023 inch, D6=0.702 to 0.708 inch, and D7 (OD of flared end of tubing)=0.66 inch. For this example, the sleeve will have an interference of two to five thousandths of an inch on each side of the flared end portion 84 of the tubing 80.
The sleeve 100 is shown in an inserted position inside the cap or nut 70 in
The sleeve member in an exemplary application provides a typical 0.003 to 0.006 inch preload on the flared portion of the tubing 80. The sleeve member as part of the fitting assembly contributes to improved leakage protection for high pressure applications. In the past, a typical leak failure may occur in a flare fitting with the nut compressing the tubing at the flare transition such as transition 86 between the flare 64C and the nut edge 74B. In the absence of a sleeve member 100, the sealing against leakage can be provided primarily by the compression at the flare transition 86, and can fail at high fluid pressures, leading to fitting leaks. However, with the sleeve 100 in place in the fitting assembly, the fluid seal is circumferential around the flared portion of the tubing surrounded by the sleeve. The nut edge 74B need not even contact or be drawn into compression against the flare transition region 86 of the tubing. This provides an increase in the fluid seal area, and thus increases the margin against leakage at higher fluid pressures. Many typical applications employ working pressures of less than 90 to 120 psi, and to provide adequate margin against pressure surges a maximum design pressure may be on the order of 2.2 times the maximum working pressure.
An exemplary embodiment of the sleeve 100 is illustrated in
In another exemplary embodiment, for a 5/8 OD ( 1/2 ID) tubing size, the sleeve may have a length of 0.54 inch, an inner diameter of 0.775 inch and an outer diameter of 0.815 inch, thus providing a sleeve wall thickness of 0.040 inch. In this example, the radius portion 102A has a radius of 0.010 inch.
It is preferable that the flared end portion 84 of the tubing 80 have a uniform thickness and inner diameter, to facilitate positioning of the sleeve 100 over the flared end portion. Some flare fabrication techniques have in the past provided flexible tubing with uneven flare wall thicknesses, so that the wall thickness on one side of the flare may be thinner than the wall thickness on the opposite side of the flare. U.S. Pat. No. 7,604,472 describes a system and method for fabricating flared ends of flexible tubing which provides excellent uniformity in the dimensions of the flared ends. In a preferred embodiment, the flared end portion 84 of the tubing 80 has been fabricated by a method and apparatus as described in U.S. Pat. No. 7,604,472, the entire contents of which are incorporated herein by this reference. Preferably the wall thickness of the flared end of the tubing being covered by the sleeve will have a tolerance of within plus or minus two thousandths of an inch, readily achievable by the fabrication techniques described in U.S. Pat. No. 7,604,472.
An exemplary embodiment of the sleeve member 100 is fabricated by injection molding, e.g. using standard thin wall injection molding procedures. Such procedures may include the use of multiple gates, sub gates, tunnel gates or hot gates to achieve the provide flow of the material into the mold.
The fitting system may be configured for connection to tubing of various sizes, for example, tubing ODs of 1/4 ( 5/32 ID), 3/8 OD (0.25 inch ID), 1/2 OD ( 3/8 ID), 5/8 OD (0.5 ID), 3/4 OD ( 5/8 ID), 1 OD ( 7/8 ID), 1 1/4 OD (1.10 ID), all dimensions in inches.
While the fitting assembly 50 provides for connection of a single tubing to the fitting, in other embodiments, multiple tubes may be accommodated. For example,
Although the foregoing has been a description and illustration of specific embodiments of the subject matter, various modifications and changes thereto can be made by persons skilled in the art without departing from the scope and spirit of the invention.
