Abstract:
An equalizer valve for a flapper in a subsurface safety valve is described. A tapered plunger is biased by compact spring disposed in the plunger bore. The spring is supported by a C-shaped ring extending into a peripheral groove around the plunger bore.

Description:
This application claims benefit of Prov. No. 60/251,224 filed Dec. 5, 2000. 
    
    
     FIELD OF THE INVENTION 
     The field of this invention related to equalizing valves mounted in ninety degree rotatable closure members, known as flappers, and more particularly to biasing systems to keep such equalizing valves in a closed position. 
     BACKGROUND OF THE INVENTION 
     Typically, a well completion includes a sub-surface safety valve. This valve is actuated from the surface using a hydraulic control system with control lines running from the surface to the valve location. These valves feature a closure member which is rotatable through an arc of ninety degrees. The control system pressure is used to move a hollow tube, known as a flow tube, downwardly, usually against a return spring. The downward movement of the flow tube rotates the flapper downwardly and out of the way to allow flow from the producing formation to reach the surface through the flow tube. Removal of pressure from the control system allowed the return spring to bias the flow tube upward, whereupon another spring on the flapper urged it to the closed position, blocking the opening in the flow tube. 
     With the flapper in the closed position, formation pressure builds up on the closed flapper. In this intended mode of operation, the flapper holds back the flow from the formation in order to allow for safe well operation. The problem that arises occurs when the well needs to be placed in service at a later time. The flapper must then be opened. However, at this time there may be substantial differential pressure acting on substantially the entire cross-sectional area of the flapper. Aggravating this differential pressure problem would be a situation in the well bore above the closed flapper where thousands of feet of the tubing was gas filled or filled with a light density fluid. The presence of gas or light weight fluids above the flapper had, in the past, required that such fluids be replaced with heavier fluid to eliminate or reduce differential pressure across the flapper prior to actuation of the flow tube. The fluid replacement procedure was costly as well as time consuming and better methods were developed to expedite the re-opening of the flapper under conditions of high differential pressure. 
     The equalizing valve in the flapper design was developed to addressed this issue. This prior art design is illustrated in FIG. 1. A flapper  10  is shown in perspective with a vertical segment  12  machined out adjacent an edge  14 . Undercuts  16  and  18  straddle the vertical segment  12  to allow for placement of a leaf spring  20  therein. Leaf spring  20  straddles bore  22  in which is disposed a plunger  24 . Plunger  24  has a taper  26  which is biased against a mating edge or surface in bore  22 . The plunger  24  is situated so that a flow tube(not shown), when urged downwardly by a control system will first contact plunger  24  and move it against the bias of leaf spring  20 . Thus, before the flapper  10  begins to move, the taper  26  has come off of its mating edge or surface in the bore  22  to equalize pressure on the flapper  10 . Those skilled in the art will appreciate that the view in FIG. 1 illustrates the down hole side of the flapper and that the flow tube is positioned on the opposite side of the flapper from which location it can make initial contact with the extending plunger  24 . 
     There was a weakness in the design described above which, in some cases, resulted in leakage past taper  26  and its mating surface in bore  22 . The reason this happened is directly related to the amount of the flapper  10  that had to be machined away to form the removed vertical segment  12  and its adjacent undercuts  16  and  18 . The removal of so much metal to accommodate the leaf spring  20  weakened the flapper  10  sufficiently to allow distortion of bore  22  with resulting leakage past taper  26 . 
     Accordingly, the objective of the present invention is to improve the design of the prior art FIG. 1 so as to eliminate the leakage problem under conditions of high differential pressure across the flapper  10 . This and other advantages will become apparent to those skilled in the art from a review of the preferred embodiment, described below. 
     Relevant to the present invention are U.S. Pat. Nos. 6,079,947; 5,884,705; 5,503,229; and 5,752,569. 
     SUMMARY OF THE INVENTION 
     An equalizer valve for a flapper in a subsurface safety valve is described. A tapered plunger is biased by compact spring disposed in the plunger bore. The spring is supported by a retaining ring which may be a C-shaped ring extending into a peripheral groove around the plunger bore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art equalizer design for a flapper: 
     FIG. 2 is a perspective view of the equalizer valve of the present invention; 
     FIG. 3 is an elevational view of the equalizer valve of the present invention; 
     FIG. 4 is an exploded view of the equalizer valve of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 3, the flapper  28  is shown to best illustrate the extension of the plunger  30  so as to position it for selective contact with a downwardly moving flow tube, schematically represented by arrow  32 . Plunger  30  resides in bore  34 , which is preferably narrow. Bore  34  has a mill flat  36 , best seen in FIG.  4 . The plunger  30  has a mating taper  38  which makes sealing contact with mill flat  36 . Other configurations for sealing apart from mill flat  36  and taper  38  can be used without departing from the invention. For example, sealing can be metal to metal at an end of plunger  30 . Alternatively the sealing can involve a resilient seal or seals or could involve metal to metal contact at other locations of plunger  30 . 
     A bias onplunger  30  is provided by a spring  40  which is retained in bore  34  by a retainer such as c-ring  42 . In the preferred embodiment the spring  42  is a wave spring. This type of spring is preferred because it provides a relatively large closing force when longitudinally compressed a short distance as compared with, for example, a coiled spring. Wave springs are available from Smalley Steel Company of Wheeling, Ill. They feature the ability to fit in small spaces and yet to provide the requisite force. In the case of a flapper  28  there is a limited space available dictated by the thickness near edge  44  where contact with the flow tube (represented by arrow  32 ) has to occur. 
     FIGS. 2 and 4 illustrate how much less metal needs to be removed to accommodate spring  40  than the prior art design depicted in FIG.  1 . Very little material beyond the diameter of taper  38  on plunger  30  needs to be removed. A peripheral groove  46  is machined in bore  34  to accept a retainer, such as, the c-ring  42 , as shown in FIG.  3 . Spring  40 , supported by c-ring  42  puts a closing force on plunger  30  by forcing its taper  38  against mill flat  36  in bore  34 . This closing force is overcome by the flow tube force represented by arrow  32  such that equalizing across flapper  28  occurs before the flapper  28  is actually rotated by the flow tube itself. 
     Those skilled in the art will notice that the removed segment  48  out of flapper  28  is considerably smaller than the vertical segment  12  and undercuts  16  and  18  shown as removed from flapper  10 . As a result, under extreme differential pressures there is no distortion in bore  34  which could cause leakage between mill flat  36  and taper  38 . 
     Removed segment  48  may be slightly larger than bore  34  to facilitate the machining of groove  46  and the subsequent insertion of c-ring  42 . 
     While spring  40  is preferably a wave spring other types of low profile biasing mechanisms are within the scope of the invention. Such alternatives can include coil springs or one or more Belleville washers. Yet other biasing systems that permit a minimization of the size of removed segment  48  are within the scope of the invention. 
     The above description of the preferred embodiment is illustrative and is not intended to be the full limits of the invention which is depicted in the claims which appear below.