The present invention relates to a fitting for soft tubing such as polyvinylchloride (PVC) tubing. More particularly, the present invention relates to a fitting including a sliding mandrel over which the tubing is inserted, the sliding mandrel providing a dynamic sealing wedge between the fitting and the tubing.
Soft tubing has been known for many years. While soft tubing is made from many different materials, such as polyvinylchloride (PVC), one of the most well known trade brands of soft tubing is TYGON (a trademark of the Norton Company) tubing. Today, TYGON tubing as well as other soft tubing is sold extensively throughout the world for many applications such as food, chemical, and medical industries, where its clarity, compatibility, chemical resistance, and extreme flexibility are particularly advantageous. There is a substantial need for a fitting particularly adapted for use with soft tubing or the like and which is easy to use.
Tubing fittings have long been known for rigid and semi-rigid tubing. Oftentimes, the fittings have been designed for rigid tubing, e.g. metal tubing, and adapted to semi-rigid tubing, e.g. plastic and nylon tubing. These tubing fittings are generally considered as a "ferruled" style tubing fitting which includes a fitting body that has specific contours for the ferrule seat, a particular ferrule that is designed to grip or seal on the outside of the tubing, and a nut portion to activate the ferrule action.
Other tubing fitting styles, including compression fittings, flared tubing fittings, etc., originally designed for use with rigid tubing, have been adapted for use with semi-rigid tubing.
However, none of these tubing fittings have been designed for reliable use with soft tubing such as TYGON tubing. Attempts have been to adapt such fittings for soft tubing by using an adaptor sleeve inserted inside the soft tubing so as to provide the soft tubing with some rigidity for the ferrule design to seal on the outside of the tubing.
Another type of fitting currently used with soft tubing is the "barbed" fitting. These fittings include a generally tubular portion having barbs or serrations on the outer surface, the tubular portion being adapted for insertion a limited distance into the end of the tubing. Consequently, the barbed fittings provide a gripping action when the tube is compressed by insertion over the barbs. The soft tubing is normally further compressed over the barb using a clamp to compress the tubing onto the barbed fitting.
Currently available ferruled and barbed fittings are not reliable for use with soft tubing. One reason for this is the unique characteristic of soft, flexible tubing which allows the cross section to reduce or become narrower as tensile pull is exerted on the tubing due to pressure inside the tubing or an external force being physically applied by a pull on the tubing. Conventional ferruled fittings will not reliably hold the tubing because the ferrule is gripping the tubing outside diameter which decreases in size as the tube is stretched. Barbed type fittings rely on the clamp being tightened so as to stretch or squeeze the tubing over the barbs so as to not allow additional stretch of the tubing. The clamp must be installed manually and additional tools and space for installation are frequently required in an effort to adequately stretch the tubing such that it is held in place by the clamp. Due to this and other differences between soft, flexible tubing and rigid or semi-rigid tubing, the standard ferruled fittings and barbed fittings currently available when utilized with soft, flexible tubing provide less than reliable results.
Couplings for large diameter hoses, such as fire hoses, have been developed which are responsive to pressure changes in the fluid, e.g. water. For example, U.S. Pat. Nos. 3,222,091; 3,226,137; 2,940,778; and 4,157,843 disclose various types of large diameter hose couplings and menders having axially slideable members responsive to water pressure changes. However, in addition to many other problems and differences, these couplings are not adaptable for soft tubing use. The large hose couplings do not lend themselves to miniaturization as required for most soft tubing applications. Furthermore, they have a rather complicated structure with several interrelated working parts. Accordingly, they appear difficult to assemble and rather expensive to manufacture.
Also, the walls of large diameter hoses do not undergo a substantial reduction in thickness that soft tubing does when subjected to a tensile pull. The hose couplings disclosed do not provide for the concentration of a wedging force. If it were possible to adapt these couplings to soft tubing, as with other coupling for rigid and semi-rigid tubing, the soft tubing would pull out from the couplings when subjected to sufficient tensile pull.
The present invention solves these and many other problems associated with currently available fittings.