Intrinsic gauging for Compression on tube fittings
The present invention relates to Compression on tube fittings of the type that use one or more ferrules for gripping a tube end. More particularly, the invention relates to apparatus and methods for visual verification that the fitting has been properly pulledup.
Thetapered front end of the front ferrule initially engages the camming mouth of the coupling body and a tapered front end of the rear ferrule initially engages a camming surface at the back end of the front ferrule. The coupling nut has a shoulder thatdrivingly engages a back wall of the rear ferrule. A tube end is axially inserted into the fitting until the tube end abuts the inner shoulder stop of the coupling body. Upon relative rotation of the coupling body and nut which drives the couplingcomponents axially towards each other, the tapered ferrules are axially pulled together, commonly referred to in the art as being “pulled-up”, and radially displaced inwardly to cause a sequential inward gripping of the tube.
During remake of the fitting, typically the relative rotation between the coupling nut and body requires fractionally more turns than is required for initial pull-up, or in other words the axial displacement of the coupling nut towards the couplingbody is slightly greater each pull-up compared to the previous pull-up operation. A manufacturer may determine a recommended number of remakes or axial displacement of the coupling nut with respect to the coupling body based on a predetermined amount oraxial displacement beyond the initial pull-up position.
In accordance with another aspect of the invention, the marking may be formed with a predetermined axial dimension and precisely located on the coupling body so that upon proper initial pull-up the coupling nut aligns with a leading edge of themarking; and upon a predetermined additional axial displacement of the coupling nut relative to the coupling body during subsequent remakes, the nut covers the marking or aligns with a trailing edge of the marking.
The precise location and positioning of the trailing edge 50b is used asa marker so that the assembler can pull-up the fitting 10 by advancing the coupling nut 14 relative to the coupling body 12 to the proper initial position, referred to herein as the “predetermined initial pull-up”. This predetermined initial pull-upcondition corresponds to a predetermined initial axial position of the nut 14 relative to the body 12 for initial pull-up to swage the ferrules 32, 34 onto the tube wall C. To aid in the visual perception of the groove 50 before the assembly is in thepulled-up condition, the groove 50 can be colored as by applying a paint or other coloring material to the visually perceptible surface, such as the bottom groove surface 58.
For smaller Compression on tube fittings, for example Compression on tube fittings used on one-quarter (1/4) to one (1) inch tubing, there istypically a relative rotation of one and a quarter “turns past finger tight” (“TPFT”) position to achieve proper initial pull-up.
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