Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
1998-12-28
2001-01-16
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C277S448000
Reexamination Certificate
active
06173965
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to valve actuators and, more particularly, to apparatus and methods for an actuator seal bearing assembly.
2. Description of the Background
Pneumatic actuators for pneumatically controlling valves are used throughout industry for a wide variety of purposes. For some applications, it is highly desirable that the actuator be as compact as possible because physical space for the valve and actuator is quite limited.
An exemplary and highly compact configuration for a pneumatic actuator is shown in U.S. Pat. No. 4,354,424, issued Oct. 19, 1982, to Sven Nordlund, which is hereby incorporated herein by reference. In that actuator, each actuator piston is provided with a rack having teeth thereon to engage corresponding teeth of an operating element. The rack includes a recess for receiving a first spring that produces a return force on the piston. The recess extends substantially into the rack of the piston. A second shorter spring is provided within a central portion of each actuator piston. Thus, one spring in each piston is off-set from the center and is longer than the other spring. The offset, longer spring provides a solution to a basic problem of compact spring return actuators. Prior to this invention, such actuators did not consistently have sufficient spring force to completely close the valve. While the off-set spring is therefore very advantageous, when the actuator is operated under full or near full load over a large number of cycles, a very slight tilting of the actuator piston can occur that may cause scoring of the cylinder and reduce the lifetime operation of the actuator. While most control systems are designed with ample safety factors that place the actuator under a relatively light load, a particular system may be designed to require a higher load with a small actuator due to limited space. As well, a system component of any control system may change or malfunction and thereby place a higher load on the actuator until the problem is detected and then corrected. Thus, it would be very desirable to increase the reliability of the compact actuator for the circumstance of high loading with continuous cycling operation.
While it would be desirable to limit wear even under a maximum load scenario, there are constraints. It would be desirable to eliminate the wear without increasing the length of the piston. The extremely compact configuration of the exemplary actuator discussed above is another significant advantage of this design. Moreover, it would be desirable to provide a means to easily update existing actuators so that if and when they are operated at full or near full load, then the lifetime will be substantially as extensive as though it were operated at only a much smaller load. Those skilled in the art have long sought and will appreciate the present invention which addresses these and other problems.
SUMMARY OF THE INVENTION
The seal bearing assembly and method of the present invention ensures long actuator life with continuous cycling at full load capacity. The present invention is especially suitable for use in a short piston so as to provide a very compact actuator. Thus, the seal bearing assembly of the present invention may be used in a pneumatic actuator piston that is reciprocal within an actuator cylinder wherein the actuator cylinder has a cylindrical surface. The pneumatic actuator piston defines therein a piston groove that encircles the pneumatic actuator piston. The piston groove has a groove width and a bottom groove surface. The seal bearing assembly comprises in the first place a compressible seal ring for encircling the pneumatic actuator piston such that the compressible seal ring is mountable or insertable into the piston groove. The compressible seal ring is sealingly engagable between the bottom groove surface and the cylinder surface so as to provide a seal around the piston within the actuator cylinder. A preferably non-metallic and substantially non-compressible bearing ring is insertable for mounting within the piston groove adjacent the compressible seal ring so as to encircle the pneumatic actuator piston. The bearing ring is sized to engage the bottom groove surface and the cylinder surface such that the bearing ring extends slightly radially outwardly from the pneumatic actuator piston to thereby engage the cylinder surface. Thus, the bearing ring substantially centers the pneumatic actuator piston within the actuator cylinder to prevent metal-to-metal contact between the pneumatic actuator piston and the cylinder surface. The bearing has a lateral support side that is engageable with the compressible seal ring. The lateral support side defines therein a concave groove. The concave groove has a profile that substantially mates to an outline of the compressible ring seal formed after the compressible ring is compressed between the cylinder surface and the bottom groove surface. Thus the compressible seal ring has an uncompressed cross-sectional profile or diameter and a different compressed seal ring cross-sectional diameter wherein the diameter is measured substantially along the line parallel to the reciprocal movement of the pneumatic piston. The bearing ring also has a bearing ring cross-sectional diameter wherein the diameter is also measured substantially along the line parallel to the reciprocal movement of the pneumatic piston. Since the bearing ring is substantially non-compressible, the profile of the bearing ring does not change. The uncompressed cross-sectional diameter of the seal ring combined with the cross-sectional diameter of the bearing ring is less than the piston groove width when the pneumatic actuator piston is not within the actuator cylinder so that the compressible seal ring is not compressed between the actuator cylinder and piston groove bottom surface. On the other hand, the compressed cross-sectional diameter of the seal ring combined with the cross-sectional diameter of the bearing ring is equal to the piston groove width when the pneumatic actuator piston is compressed within the actuator cylinder such that the compressible seal ring and the bearing ring are restricted from side-to-side movement within the piston groove width of the piston groove as the pneumatic actuator piston reciprocates within the actuator cylinder.
Moreover, the compressible seal ring preferably has a circular uncompressed cross-section. This circular uncompressed seal ring cross-section has a first radius. The concave groove has a substantially circular arc-shaped groove with a second radius. In a presently preferred embodiment of the invention, the first radius is greater than the second radius.
In another aspect of the invention, the bearing ring has a cross-sectional profile with a chamferred corner on an opposite side of the bearing ring from bearing ring concave groove.
The method for using/making a seal bearing assembly for a compact actuator comprises providing a piston with a single piston groove for the seal bearing assembly. The use of only a single piston groove thereby controls the overall length of the piston. A compressible seal ring is provided that has a substantially circular cross-section when uncompressed. The substantially circular cross-section has a first radius. A bearing ring with a bearing groove along a first lateral side thereof is provided. The groove is substantially arc-shaped and has a second radius. In a preferred embodiment, the second radius is less than the first radius. The compressible seal ring is positioned within the single groove for the seal bearing assembly. The bearing is positioned within the single groove adjacent to the compressible seal ring such that the bearing groove along the first lateral side thereof directly faces the compressible seal ring.
Preferably, the compressible seal ring and the bearing ring are sized such that the compressible seal ring and the bearing ring are moveable within the single piston groove when the piston is outside of the compact actuator in which the pis
Knight Anthony
Nash Kenneth L.
Pilaud Robert L.
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