Pipe joints or couplings – Packed – Wedge
Reexamination Certificate
2000-09-08
2002-09-17
Browne, Lynne H. (Department: 3679)
Pipe joints or couplings
Packed
Wedge
Reexamination Certificate
active
06450550
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to tube fittings for systems or equipment using tubing to conduct gasses or liquids and more particularly relates to tube fittings for retaining tubes used with vibrating equipment such as air compressors and hydraulic and pneumatic systems for transportation vehicles.
Reciprocating equipment such as air compressors operate at elevated temperatures, deliver a pulsating stream of fluid and vibrate considerably. Hydraulic and pneumatic systems used for controls and for brakes in trucks, buses, off-highway vehicles, locomotives and other transportation equipment also operate in hot environments. Components of these systems are subject to vibration caused by engines propelling the equipment and as a result of uneven roadways over which the equipment travels. Air compressors and other pneumatic and hydraulic equipment use fittings to connect tubing to conduct gasses and liquids to and from that equipment. Due to strong market competition, manufacturers are in a constant race to design and manufacture components, such as tube fittings for this type of equipment, more inexpensively, while maintaining a required level of quality and durability.
The various types of fittings currently in use all have their advantages, as well as offsetting disadvantages.
Compression fittings compress metal ferrules about a tube within the fitting to hold the tube. While they are one of the least expensive types of fittings, installation of tubes into compression fittings is difficult.
FIG. 1
shows a compression fitting
20
having a body
22
with a bore
24
at one end surrounded by male threads
26
. A nut
28
fits on the threads
26
of the body
22
. A ferrule
30
is placed over a tube
32
which is to be held by the fitting
20
. The ferrule
30
has sloped end surfaces
33
which allow it to be compressed by an inside surface
34
of the bore
24
. The tube
32
, with the ferrule over it, is inserted into the fitting body and the nut
28
is threaded onto the threads
26
of the body
22
. The nut
28
is tightened with a wrench to compress the ferrule
30
around the tube, securing and sealing the tube.
When metal ferrules are used to crimp metal tubing, early tube failures often occur due to fatigue caused by machine vibration. Crimping also reduces the inside diameter of the tube, reducing flow capacity. Some compression type fittings use soft Teflon or silicone ferrules in place of metal ferrules. While the soft ferrules may minimize tube breakage due to fatigue, the soft ferrules are known to fail prematurely by wearing out and leaking. The soft ferrules also make assembly more difficult.
Flare fittings have been used to retain tubes for applications having significant vibrations, such as air compressors. A flare fitting
36
is shown in FIG.
2
. The flare fitting
36
has a body
38
having a bore
40
at one end, surrounded by internal threads
42
forming a nut. The flare fitting
36
also includes a retainer
44
having external threads
46
which intermesh with the threads
42
on the body
38
. The retainer
44
has a central hole within it into which tubing
48
is inserted. A flare
50
is formed in the end of the tubing
48
by a flaring tool to allow the nut at the end of the body
38
, surrounding the tubing adjacent the flare, and an internal end
52
of the retainer
44
to clamp the flare
50
between them and hold the tubing
48
tightly within the fitting body
38
.
Flare type fittings do not reduce tube life to the same extent as compression fittings, since they do not crimp the tubing and they also do not reduce the inside diameter of the tube. However, flare fittings experience failures due to fatigue at the areas of the flared tubing which contacts the members of the fitting. Additionally flare fittings are more expensive to manufacture and assemble because they tend to be larger in size and require the user to flare the tubing and are difficult to assemble.
Push-in tube fittings of the type shown in
FIG. 3
allow a tube to be connected to the fitting by pushing the tube into the fitting. A push-in fitting
53
includes a body
54
and a gripper formed by axially extending fingers
56
of a cylindrical collet
58
. Each of the distal ends
60
of the fingers
56
comprises a cam section. The cam section causes the fingers
56
to be deflected as the collet
58
is inserted into the body
54
. The cam section
60
can move outwardly into an enlarged central cylinder formed by camming surface
62
within the body
54
. An O-ring
64
is inserted within the body
54
at the end of the central cylinder
66
so as to form a seal about tubing
68
when it is inserted within the fitting
53
.
When the tubing
68
is inserted through the collet
58
, the fingers
56
are moved axially in an outward direction. The cam
60
bears against the camming surface
62
which allows the tube to be pushed within the body
54
. However, the camming surface
62
causes the fingers
56
to compress about the tubing
68
to prevent it from being removed from the fitting
53
whenever a force attempts to pull the tubing
68
out of the collet
58
. The force of the fingers
56
about a metal tubing causes the tubing or the fingers
56
to fatigue in areas where it is gripped throughout the use of the push-in fitting on equipment which is subject to vibration. This fatigue ultimately causes a failure of the tubing or the fingers
56
.
Other push-in fittings include a fitting assembly having a retaining ring with gripping teeth about its periphery rigidly installed within the body to hold tubing. These fittings also include an O-ring within the fitting to act as a seal. One such push fitting
70
, shown in
FIG. 4
, comprises a fitting body
72
and a nut
74
having internal screw threads which screw onto screw threads at the tube receiving end of the body
72
. An O-ring seal
76
is mounted within a cavity
78
in an end of the body
72
. A retaining ring
80
having gripping teeth
82
is mounted within a cavity inside the nut
74
. A spacer
84
is inserted within the cavity of the nut
74
between the retaining ring
80
and the body
72
of the fitting
70
. The spacer
84
protects the O-ring seal
76
from the gripping teeth
82
. The surface of the spacer
82
adjacent the gripping teeth
82
is canted to allow room for the gripping teeth to bend as a tube
86
is installed.
The tube
86
is installed into the push fitting
70
by sliding the tube
86
through the nut
74
and the gripping teeth
82
of the retaining ring
80
. The tube is held in place by the gripping teeth
82
. An end
88
of the nut
74
holds the retaining ring
80
in place after the nut
74
is tightened onto screw threads
90
of the body
72
.
Currently available push fittings which use retaining rings do not work well with metal tubing because the tubing fails due to fatigue where it is held by gripping teeth, such as gripping teeth
82
shown in FIG.
4
. The gripping teeth of retaining rings normally do not fail because the retaining rings are made out of spring steel which is harder than the material of the tubing. Thus, available push fittings using retaining rings require the use of plastic tubing with them. Since vibrating equipment, such as air compressors and transportation systems, operate at elevated temperatures, the tubing must be made out of more expensive, high temperature plastics such as Teflon.
Among the many patents which disclose prior art fittings of the type described above are U.S. Pat. No. 3,999,783 Andre Legris issued Dec. 28, 1996; U.S. Pat. No. 4,867,489 Hiralal V. Patel issued Sep. 19, 1989; U.S. Pat. No. 5,024,468 Donald G. Burge issued Jun. 18, 1991; U.S. Pat. No. 5,230,539 Darwin C. Olson issued Jul. 27, 1993; U.S. Pat. No. 5,584,514 Michael A. Sweeney et al. issued Dec. 17, 1996; and U.S. Pat. No. 5,683,120 David J. Brock et al. issued Nov. 4, 1997.
SUMMARY OF THE INVENTION
In accordance with this invention, a fitting for retaining a cylindrical tube includes a fitting body having a hole extending through it. The body also
Dunwoody Aaron
Goebel, Jr. Edward W.
MacDonald Illig Jones & Britton LLP
R. Conrader Company
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