Seal for a joint or juncture – Seal between relatively movable parts – Piston ring or piston ring expander or seat therefor
Reexamination Certificate
2000-06-07
2002-09-24
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S589000
Reexamination Certificate
active
06454272
ABSTRACT:
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
The present invention relates to a sealing arrangement for sealing a space, which extends between high and low pressure areas and which is defined between a first apparatus part and a cylindrical surface of a second apparatus part, the first and second apparatus parts being mutually movable in a reciprocating manner along the axis of said cylindrical surface.
As an example, the apparatus part may be part of a housing or a cylinder, and the second apparatus part may be a piston rod connected to a double acting piston. A sealing arrangement of this type is disclosed for example in WO 92/15807. This known sealing arrangement comprises an annular sealing member of resilient material and a compression ring, such as an O-ring, surrounding the annular sealing member. The radially outer peripheral surface of the annular sealing member extends between axially opposite first and second end surfaces facing said high and low pressure areas, respectively. The annular sealing member also has a radially inner peripheral surface for sealing engagement with the cylindrical surface of the second apparatus part at a contact area thereof. The purpose of the compression ring is to press the contact area of the inner peripheral surface of the sealing member into tight sealing engagement with the cylindrical surface of the second apparatus part. This means that ideally the annular contact area between the compression ring and the outer peripheral surface of the annular sealing member should be positioned radially opposite to the contact area between the sealing member and the cylindrical surface of the second apparatus part.
In actual practice, however, the pressure difference between the high and low pressure areas varies substantially, and an increasing pressure difference tends to force the compression ring and, consequently, also the contact area between the compression ring and the annular sealing member, in a direction toward the low pressure area. In order to substantially maintain the sealing pressure between the contact area of the inner peripheral surface part of the sealing member and the cylindrical surface of the second apparatus part when the compression ring is forced toward the low pressure area, the outer peripheral surface of the sealing member is chamfered at its low pressure end. Thus, the annular sealing member of the known sealing arrangement has an outer peripheral surface defining an obtuse angle in an axial sectional view.
It has been found that the compression ring, which may, for example, be an O-ring made from an elastomeric material, has a relatively short useful lifetime, because eventually the compression ring becomes permanently deformed.
SUMMARY OF THE INVENTION
The present invention provides a sealing arrangement of the type discussed above with an increased efficiency and a prolonged useful economic lifetime.
Thus, the present invention provides a sealing arrangement for sealing a space, which extends between high and low pressure areas and which is defined between a first apparatus part and a cylindrical surface of a second apparatus part, the first and second apparatus parts being mutually moveable in a reciprocating manner along the axis of said cylindrical surface, said sealing arrangement comprising an annular sealing member of resilient material having a radially outer peripheral surface extending between axially opposite first and second end surfaces facing said high and low pressure areas, respectively, and a radially inner peripheral surface for providing a sealing engagement with the cylindrical surface of the second apparatus part at a contact area, and for defining with the cylindrical surface a first space widening or diverging from said contact area towards the low pressure area; and a compression ring surrounding the annular sealing member, the compression ring being in contact with the outer peripheral surface of the annular sealing member so as to press the inner peripheral surface thereof into close contact with the cylindrical surface of the second apparatus part at said contact area; the axial sectional view of at least part of the outer peripheral surface of the annular sealing member coming into contact with the compression ring defining such convex contour that in an unstressed condition of the sealing member, the radial distance between such part of the outer peripheral surface and the radially innermost part of the inner peripheral surface is decreasing in an axial direction toward the second end surface and the low pressure area, the radius or radii of curvature of the convex contour being at least 0.4 times the total axial length or width of the annular sealing member.
It has been found that in the known sealing arrangements the efficiency of the compression ring is eventually reduced because during operation the compression ring is pressed into contact with a rather sharp annular edge defined by the outer peripheral surface of the sealing member and corresponding to the vertex of the aforesaid obtuse angle. It has been found that the useful lifetime of the sealing arrangement according to the invention is substantially prolonged compared with the lifetime of the known sealing arrangements when the convex contour of the outer peripheral surface of the annular sealing member is rounded as described above.
The radius of curvature of such rounded surfaces preferably does not exceed twice the total axial length or width of the annular sealing member, and in the presently preferred embodiment the radius or radii of curvature is/are at least 0.6 and preferably about 0.85 times the total axial length of the annular sealing member.
The convex contour of the outer peripheral surface of the sealing member may extend along the total axial length or width of the sealing member. However, when the radial distance between the outer peripheral surface of the sealing member and the cylindrical surface of the second apparatus part is gradually decreasing toward the second end surface of the sealing member or toward the low pressure area, the compression ring may tend to be forced or extruded into the space defined between the second end surface of the sealing member and an adjacent opposite surface of the first apparatus part. In order to counteract such tendency, the convex axial sectional contour of the outer peripheral surface part may continuously merge into a concave sectional contour adjacent to the second end surface of the sealing member. In such case the convex contour may merge into the concave contour at an inflexion spaced from said second end surface by a distance of 0.05-0.25 times the total axial length or width of the sealing member. The end part of the sectional contour adjacent to the second end surface of the sealing member and the longitudinal axis of the sealing arrangement preferably defines therebetween an angle from −10° to +45°. Thus, the end part of the sectional contour and the longitudinal axis of the sealing arrangement may be converging, but are preferably diverging toward the low pressure area.
The radially inner peripheral surface of the sealing member may include a first section, which extends between the first end surface of the sealing member and the contact area, and which has a minimum diameter substantially exceeding the maximum diameter of a second section of the inner peripheral surface defining said gradually widening or diverging space. Thus, the contacting area is defined as an intermediate part between the first and second sections. Thereby it is secured that the radially inwardly directed pressure applied by the compression ring is concentrated at the predetermined contact area.
The sealing member and the compression ring of the sealing arrangement according to the invention may be retained in their mutual positions in any suitable manner. In the preferred embodiment, however, the annular sealing member and the compression ring are arranged within an annular channel or groove which is formed in the first apparatus
Beres John L.
Klein Howard J.
Knight Anthony
W. S. Shamban Europa A/S
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