Wells – With below and above ground modification – Above ground actuating means for below ground device
Reexamination Certificate
2003-02-07
2004-11-02
Tsay, Frank (Department: 3672)
Wells
With below and above ground modification
Above ground actuating means for below ground device
C166S069000, C267S141000, C267S153000
Reexamination Certificate
active
06810953
ABSTRACT:
The present invention relates to the art of oil pumping and more particularly to a shock absorber for use between the reciprocating member of an oil well pumping mechanism and a polish rod connected to the downwardly extending sucker rod string.
INCORPORATION BY REFERENCE
For many years in the oil industry some of the oil well pumping units have used a shock absorber between the polish rod and operating bridle of the reciprocating pumping mechanism. When employed, these shock absorbers were normally formed from elastomeric discs, such as shown in Case U.S. Pat. No. 4,176,714; Fix U.S. Pat. No. 4,354,397; and, Clayton U.S. Pat. No. 4,445,674. These patents are incorporated by reference as a disclosure of the background to which the present invention is directed. Such technology is well known and need not be repeated in this description of the invention. Recently it has been suggested to replace the elastomeric discs by a more reliable mechanism in the form of a coil spring as shown in Pelham U.S. Pat. No. 6,446,946, also incorporated by reference herein. By using a steel coil spring, long term deterioration and wear of the shock absorber itself is reduced. Control over movement of the polish rod is drastically improved. In Pelham U.S. Pat. No. 6,446,946 the coil spring is contained in a spring housing including two telescoping cylindrical cup-shaped members. The background and technology of using a single coil spring in a shock absorber as a replacement for the elastomeric discs is disclosed in this 2002 patent.
BACKGROUND OF INVENTION
Elastomeric shock absorbers shown in Case U.S. Pat. No. 4,176,714 have been very successful in reducing the peak loads imposed by the sucker rod string during the pumping action. However, elastomeric discs tend to wear and deteriorate during long term operation, especially in adverse environments. Consequently, recently there has been an effort to replace the elastomeric discs with a mechanical device in the form of a steel coil spring, as shown in Pelham U.S. Pat. No. 6,446,946. This newly developed technology is now in its infancy and has presented practical difficulties, such as undue wear between the polish rod and the lower end plate of the spring housing. This wear is accentuated when a spring pilot is provided in the bottom cylindrical housing member to center the coil spring. Such pilot has a center opening which contacts or engages the reciprocally movable polish rod to cause wear on the polish rod due to transverse forces. This metal-to-metal wear reduces the effective life of the shock absorber and requires periodic inspection and maintenance to assure continued operation of the shock absorber in the well pumping mechanism. The pilot needs to have a given axial height and must be formed from a hard material, such as hardened steel. Thus, there is an extended clearance opening inviting substantial wear and imposing new lifting force peaks. The advantages of using a coil spring over the elastomeric discs have not fully materialized in view of certain friction action experienced in present coil spring adaptation for a standard shock absorber between the lift bridle and polish rod. This disadvantage is overcome by the present invention so a coil spring shock absorber can provide its benefits without disadvantages of the Pelham effort.
THE INVENTION
To overcome the disadvantages associated with efforts to use a coil spring in the shock absorber between the reciprocal member of the well pumping mechanism and the polish rod, a shock absorber as shown in Pelham U.S. Pat. No. 6,446,946 has been modified to include a friction reducing centering head secured to the bottom and plate. In practice, a head is used at both the top end plate and the bottom end plate. These centering heads secured to the end plates center the polish rod in the clearance opening in the end plates and hold the polish rod away from the wall surrounding the clearance opening in the end walls. The spring pilot as shown on the lower end wall of Pelham U.S. Pat. No. 6,446,946 is replaced and made as a part of the centering head on the lower end plate so that the clearance opening is not extended for increased frictional engagement as necessary in the prior art. Lateral forces are decreased. The lower, or both end plates of the shock absorber, are provided with the centering mechanism that preferably includes a spring pilot to substantially reduce the friction experienced between the polish rod as it reciprocates in the shock absorber.
In accordance with the invention, a shock absorber for use between the reciprocating member of an oil well pumping mechanism and a polish rod connected to the downwardly extending rod string comprises an upper and lower end plate. Each end plate has a peripheral surface around the axis of the shock absorber to define a polish rod clearance opening between the two end plates. A coil spring is positioned between the end plates in a position concentric with, and surrounding, the reciprocal axis of the polish rod. Attachment members secure the lower plate with the reciprocal member of the well pumping mechanism. In accordance with the invention, a friction reducing centering head is secured to lower or both of the end plates for centering the polish rod as it passes through the clearance opening and for holding the polish rod away from the peripheral wall surrounding and defining the clearance opening. Thus, the clearance openings in the end plates, especially the one in the lower plate, are larger than the polish rod and a centering head engages the reciprocating polish rod with a mechanism to reduce the friction and wear between the reciprocating polish rod and the shock absorber.
In accordance with another aspect of the present invention, the coil spring has an inside diameter and the centering head includes a generally circular spring pilot secured to the end plate. This pilot has a center opening larger than but aligned with the clearance opening of the end plate and an outer diameter slightly smaller than the inner diameter of the coil spring. Thus, the centering head on each of the end plates perform the function of reducing friction, but also performs the function of guiding the coil spring. This guiding action occurs at both the upper end plate and the lower end plate. Consequently, the coil spring is guided in its axial movement during operation of the shock absorber. This is different than Pelham U.S. Pat. No. 6,446,946 wherein the spring aligner or pilot has an opening that is a mere extension of the lower plate clearance opening of the polish rod. This prior design increases the friction between the rod and the shock absorber. Thus, efforts to incorporate the advantages of the coil spring are met with frictional disadvantages. Furthermore, the prior art does not incorporate the advantage of a spring pilot on both reciprocating end plates to guide the main spring.
In accordance with another aspect of the present invention, the centering heads each have at least three guide rolls with rotating outer cylindrical surfaces that engage the polish rod and are mounted on the spring pilot. Thus, the polish rod extends through the large clearance opening in the end plates and is engaged with inwardly extending rotating cylindrical surfaces. These rolls may be elongated or relatively short in axial length. In practice, three circumferentially spaced guide rolls are preferred. The equally spaced guide rolls are rotatably mounted on a hardened pins to reduce the friction caused by engaging and rotating with the polish rod. In accordance with an aspect of the invention, the pins are hardened and the outer surface of the rollers engaging and centering the polish rod have a lower hardness than the hardness of the polish rod. This feature can not be used in the Pelham mechanism. Consequently, even the rolling action between the polish rod and the rolls does not damage or deteriorate the surface of the polish rod. The rolls have a low hardness compared to the polish rod. The pins are hardened steel that have a reduced rotational friction to be combined w
Barnes Group Inc.
Tsay Frank
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