Abstract:
A hydraulic control system for a sub-surface safety valve has control lines in hydraulic communication with the valve. A first control line communicates hydraulic pressure to actuate the valve, while the other control line communicates hydraulic pressure to compensate for hydrostatic pressure associated with the first control line. A regulator regulates hydraulic communication between the two control lines. The regulator prevents fluid communication from the first to the balance control line as long as integrity of the second line is maintained. When the second line fails, the safety valve can fail in the open position. In this case, the regulator permits hydraulic pressure to bleed from the first line to the second line. This allows the safety valve to then fail in a closed condition and allows the second line to potentially be recharged if its integrity is regained.

Description:
BACKGROUND 
     Subsurface safety valves, such as a tubing retrievable safety valves, deploy on production tubing in a producing well. The safety valves can selectively seal fluid flow through the production tubing if a failure or hazardous condition occurs at the well surface. In this way, safety valves can minimize the loss of reservoir resources or production equipment resulting from catastrophic subsurface events. 
     A conventional safety valve uses a flapper to close off flow through the valve. The flapper, which is normally closed, can be opened when hydraulic pressure applied to a hydraulic piston move a flow tube against the bias of a spring in the valve. When the flow tube moves, it pivots the flapper valve open, allowing flow through the safety valve. 
     From the surface, a control line supplies the hydraulic pressure to operate the valve. The control line extends from a surface controlled emergency closure system, through the wellhead, and to the safety valve. As long as hydraulic pressure P C  is applied through the control line, the valve can remain in the opened position, but removal of control line pressure returns the valve to its normally closed position. The hydrostatic or “head” pressures P H  from the column of fluid in the control line can directly limit the setting depth and operational characteristics of the safety valve in such a system. 
     Historically, additional load from stronger power springs has been used to offset the hydrostatic pressure of the control line. However, safety valves have limited space available to accommodate a larger spring. In fact, the active control line hydrostatic pressure P H  can be so significant in some applications that a spring may not be able to overcome the hydrostatic pressure and the valve&#39;s flapper cannot close, assuming the wellbore pressure is zero. 
     To compensate for the control line&#39;s hydrostatic pressure P H , a gas (nitrogen) charge can be stored in the safety valve to counteract the hydrostatic pressure. Unfortunately, using a gas charge in the valve presents problems with leakage of the gas, which can cause the valve to fail in the open position. In addition, once the charge is spent in a fail-safe operation, operators must do a substantial amount of work to replace the valve. 
     In contrast to a gas charge, safety valves have been developed that use a magnetically driven device on the valve. The magnetic device allows the hydraulics to reside outside the wellbore and may use annulus pressure to offset the hydrostatic pressure of the control line so that the safety valve can be set at greater depths. Unfortunately, using such an arrangement may be undesirable in some applications. 
     In yet another solution, a second “balance” control line has been used with a deep-set safety valve to negate the effect of hydrostatic pressure P H  from the active control line. In these existing balance line valves, the second balance line acts on the valve&#39;s piston against the pressure from the active control line to balance the hydrostatic pressure P H  from the active control line Therefore, because the underside of the piston is in fluid communication with the balance line, the piston is no longer in fluid communication with the tubing. Accordingly, any beneficial effect produced by the tubing pressure P T  in operating this type of deep-set safety valve is not utilized. 
     A different type of balance line arrangement shown in  FIG. 1  is disclosed in U.S. Pat. No. 7,392,849, which is assigned to the Assignee of the present disclosure and is incorporated herein in its entirety. Production tubing  20  has a deep-set safety valve  50  for controlling the flow of fluid in the production tubing  20 . In this example, the wellbore  10  has been lined with casing  12  with perforations  16  for communicating with the surrounding formation  18 . The production tubing  20  with the safety valve  50  deploys in the wellbore  10  to a predetermined depth. Produced fluid flows into the production tubing  20  through a sliding sleeve or other type of device. Traveling up the tubing  20 , the produced fluid flows up through the safety valve  50 , through a surface valve  25 , and into a flow line  22 . 
     As is known, the flow of the produced fluid can be stopped at any time during production by switching the safety valve  50  from an open condition to a closed condition. To that end, a hydraulic system having a pump  30  draws hydraulic fluid from a reservoir  35  and communicates with the safety valve  50  via a first control line  40 A. When actuated, the pump  30  exerts a control pressure P C  through the control line  40 A to the safety valve  50 . 
     Due to vertical height of the control line  40 A, a hydrostatic pressure P H  also exerts on the valve  50  through the control line  40 A. For this reason, a balance line  40 B also extends to the valve  50  and provides fluid communication between the reservoir  35  and the valve  50 . Because the balance line  40 B has the same column of fluid as the control line  40 A, the outlet of the balance line  40 B connected to the valve  50  has the same hydrostatic pressure P H  as the control line  40 A. 
     Internally, components of the safety valve  50  are exposed to control pressure P C  from the control line  40 A and the offsetting hydrostatic pressure P H  from the balance line  40 B. Yet, the components are also exposed to tubing pressure P T  in the well during operation, which can be beneficial. As briefly illustrated in  FIGS. 2A-2B , the deep-set safety valve  50  uses the hydraulic pressures from the two control lines ( 40 A-B) so the valve  50  can be set at greater depths downhole. The valve  50  as illustrated in  FIGS. 2A and 2B  has first and second actuators  60 A-B. The first actuator  60 A has an active piston  62 A coupled to a flow tube  54 . Control pressure from the primary control line ( 40 A) moves the control piston  62 A and the flow tube  54  against the bias of a spring  56  to open the valve&#39;s flapper (not shown). The second actuator  60 B has a balance piston  62 B that can intermittently engage the flow tube  54  during operation. 
     In  FIG. 2A , the valve  50  is in a closed condition where the balance piston  62 B is idle in which case the tubing pressure P T  is greater than the hydrostatic pressure P H . By contrast, the valve  50  is in an opened condition in  FIG. 2B . As shown in  FIG. 2A , if the tubing pressure P T  is substantial, then force from this tubing pressure P T  and from the spring  56  exerts on the control piston  62 A and tends to close the valve  50 . Since the tubing pressure P T  is greater than P H  in  FIG. 2A , however, the balance piston  52 B is idle as it exerts no force on the flow tube  54  because a net downward force exerted by the tubing pressure P T  keeps the balance piston  62 B resting on a shoulder  57 . 
     As shown in  FIG. 2B , if the hydrostatic pressure P H  is substantial, a force exerts on the control piston  62 A and tends to open the valve  50 . Likewise, control pressure P C  from the control line ( 40 A) exerts on the control piston  62 A and tends to open the valve  50 . Yet, the hydrostatic pressure P H  exerts an opposing force on the balance piston  62 B, thereby tending to close the valve  50 . Additionally, the tubing pressure P T  exerts an opposing force on the balance piston  62 B; however, this force does not tend to open the valve  50  because the balance piston  62 B is structurally isolated from the flow tube  54  (and the spring  56 ) by interaction of a block  55  with the shoulder  57  of the chamber housing. Thus, if the control pressure P C  is reduced in  FIG. 2B , the valve  50  will revert to the closed condition shown in  FIG. 2A . 
     Although existing safety valves for deep-set applications may be effective, operators are continually seeking improved hydraulic control systems for deep-set applications that can avoid failures and mitigate other problems. The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
     SUMMARY 
     A hydraulic control system for a sub-surface safety valve has first and second control lines in hydraulic communication with the sub-surface safety valve. The first control line communicates first hydraulic pressure to actuate the sub-surface safety valve. The second control line communicates second hydraulic pressure to compensate for hydrostatic pressure associated with the first control line. A regulator regulates hydraulic communication between the first and second control lines. The regulator can affix to production tubing and can be plumbed between the two control lines downhole. Alternatively, the regulator can be installed on or incorporated into the safety valve itself or some other tubing component downhole. 
     In general, as long as the second hydraulic pressure compensates for the hydrostatic pressure in the first control line, the safety valve can operate appropriately. In this case, the regulator prevents fluid communication from the first control line to the second control line. However, when the second hydraulic pressure falls below a particular level related to the hydrostatic pressures associated with the first control line, the safety valve can fail in the open position depending on the pressure in the well. In this case, the regulator permits hydraulic communication from the first control line to the second control line. As hydraulic pressure bleeds from the first line to the second line, the hydraulic pressure from the first line may fall below a particular level. Assisted by the spring (and potentially by tubing pressure as well), the safety valve can then fail in the closed condition instead of remaining open. Eventually, the hydraulic pressure bled from the first control line may charge the second control line if the second line&#39;s integrity is regained. In this way, the safety valve can then be reset. 
     The first control line extends from the sub-surface safety valve uphole through a wellhead, where the first control line couples to a hydraulic system, having a pump and reservoir. The second control line can also extend from the sub-surface safety valve up through the wellhead and can couple to a pump or a reservoir of the hydraulic system. Alternatively, the second control line extends from the sub-surface safety valve, but it terminates at some point downhole from the wellhead. In this case, the second control line can have a cap. When the production tubing with the safety valve and control lines is deployed downhole, the second control line may be evacuated of hydraulic fluid. Once deployed, hydraulic pressure can be bled from the first control line to the second control line through the regulator to an appropriate pressure for the deep-set operation of the safety valve. Any trapped gas in the second control line can then be used as a compressible buffer for the line, which may be advantageous for its operation. 
     The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a wellbore having a string of production tubing and a deep-set safety valve in accordance with the prior art. 
         FIGS. 2A-2B  illustrate details of the deep-set safety valve of the prior art. 
         FIGS. 3A-3C  illustrate configurations of a control system in accordance with the present disclosure for a deep-set safety valve. 
         FIGS. 4A-4B  illustrate configurations for affixing the control system on production tubing having a deep-set safety valve. 
         FIGS. 5A-5B  illustrate cross-sections of a regulator in closed and opened conditions for the disclosed control system. 
     
    
    
     DETAILED DESCRIPTION 
     A dual line control system  100  in  FIGS. 3A-3C  operates with a deep-set safety valve  50 . As described previously, the safety valve  50  installs on production tubing (not shown) disposed in a wellbore, and the safety valve  50  controls the uphole flow of production fluid through the production tubing. In use, the safety valve  50  closes flow through the tubing in the event of a sudden and unexpected pressure loss or drop in the produced fluid, which coincides with a corresponding increase in flow rate within the production tubing. Such a condition could be due to the loss of flow control (i.e., a blowout) of the production fluid. During such a condition, the safety valve  50  automatically actuates and shuts off the uphole flow of production fluid through the tubing. When control is regained, the safety valve  50  can be remotely reopened to reestablish the flow of production fluid. 
     The control system  100  includes a well control panel or manifold of a hydraulic system  110 , which can have one or more pumps  112 , reservoirs  114 , and other necessary components for a high-pressure hydraulic system used in wells. In  FIG. 3A , two control lines  120 A-B extend from the hydraulic system  110  through the wellhead  115  and down the well to the deep-set safety valve  50 . One of the control lines  120 A couples to the pump  112  of the hydraulic system  110 , while the other control line  120 B couples to the reservoir  114  of the hydraulic system  110  in a manner similar to that described in U.S. Pat. No. 7,392,849, which has been incorporated herein by reference in it its entirety. 
     In  FIG. 3B , two control lines  120 A-B extend from the hydraulic system  110  through the wellhead  115  and down the well to the deep-set safety valve  50 . In this configuration, however, both control lines  120 A-B couple to the one or more pumps  112  of the hydraulic system  110  and are separately operable. Using this configuration, operators can open and close the deep-set safety valve  50  in both directions with hydraulic fluid from the control lines  120 A-B being separately operated with the hydraulic system  110 . Either way, the balance control line  120 B in  FIGS. 3A-3B  can offset the hydrostatic pressure in the primary control line  120 A, allowing the safety valve  50  to be set at greater depths. 
     Passing control lines through the components of the wellhead  115  can be complicated. As another alternative, the configuration of the control system  100  in  FIG. 3C  has the balance control line  120 B terminated or capped off below the wellhead  115 . Thus, only the primary control line  120 A runs to the surface and the hydraulic system  110 , while the balance control line  120 B for offsetting the hydrostatic pressure terminates below the wellhead  115  with a cap  130 . In this way, the configuration of  FIG. 3C  eliminates the need for passing two control lines through the wellhead  115 . 
     For its part, the safety valve  50  in  FIGS. 3A-3C  can include any of the deep-set valves known and used in the art. In one implementation, the deep-set safety valve  50  can have features such as disclosed in incorporated U.S. Pat. No. 7,392,849. In general, the deep-set safety valve  50  uses hydraulic pressures from the two control lines  120 A-B to actuate a closure  65  of the valve  50  so the valve  50  can be set at greater depths downhole. As best shown in  FIG. 3A , for example, the primary or active control line  120 A can operate a primary actuator  60 A in the valve  50 , while the second or balance control line  120 B can operate a second actuator  60 B. As shown, the closure  65  can include a flapper  52 , a flow tube  54 , and a spring  56 . The primary actuator  60 A can include a rod piston assembly known in the art for moving the flow tube  54 . The balance actuator  60 B can also include a rod piston assembly known in the art for moving the flow tube  54 . 
     Alternatively, the balance actuator  60 B can include the balance control line  120 B communicating with a chamber for the spring  56  so second hydraulic pressure in the balance control line  120 B can act in conjunction with the spring  56  against the flow tube  54 . Moreover, the balance control line  120 B can communicate with an opposing side of the piston assembly of the first actuator  60 A to balance the hydrostatic pressure in the first control line  120 A. Alternatively, the control lines  120 A-B can couple to actuators in the safety valve  50  in accordance with the arrangement disclosed in incorporated U.S. Pat. No. 7,392,849, which allows tubing pressure to be utilized. These and other actuators  60 A-B and closures  65  can be used in the safety valve  50  for the disclosed control system  100 . 
     Either way, with the primary control line  120 A charged with hydraulic pressure, the primary actuator  60 A opens the closure  65 . For example, the piston of the actuator  60 A moves the flow tube  54  down, which opens the flapper  52  of the safety valve  50 . For its part, the hydraulic pressure from the balance control line  120 B offsets the hydrostatic pressure in the primary control line  120 A by acting against the balance actuator  60 B. For example, the balance actuator  60 B having the balance piston assembly acts upward on the flow tube  54  and offsets the hydrostatic pressure from the primary control line  120 A. Therefore, this offsetting negates effects of the hydrostatic pressure in the primary control line  120 A and enables the valve  50  to operate at greater setting depths. 
     If the balance control line  120 B loses integrity and insufficient annular pressure is present to offset the primary control line&#39;s hydrostatic pressure, then the valve  50  can fail in the open position, which is unacceptable. The control line  120 B, which may be %-inch diameter tubing, can fail due to various reasons. For example, the control line  120 B can leak, or it can become contaminated or blocked over time due to debris in the control fluid. Typical debris, contamination, or particles that can develop and become suspended in the control fluid can come from reservoirs, physical wear of system components, chemical degradation, and other sources. 
     To overcome unacceptable failure, the control system  100  includes a fail-safe device or regulator  150  disposed at some point down the well. The regulator  150  interconnects the two control lines  120 A-B to one another and acts as a one-way valve between the two lines  120 A-B. Under certain circumstances discussed later, the regulator  150  bleeds pressure from the primary control line  120 A to the balance control line  120 B to facilitate operation of the safety valve  50 . 
     Briefly,  FIG. 4A  shows an arrangement for affixing the control lines  120 A-B to production tubing  20  having the deep-set safety valve  50 . The control lines  120 A-B can use straps or bandings  24  typically used to attach control lines to tubing. The regulator  150  can be an independent component coupled by flow tees or other necessary components to the control lines  120 A-B and can also affix to the tubing  20  with bandings  24 . Alternatively, as shown in  FIG. 4B , the regulator  150  can be installed on or incorporated into the housing of the safety valve  50  or some other tubing component downhole, while the control lines  120 A-B affix with bandings  24  or the like. The banding and other arrangements can be used to install the control system  100  on the tubing  20 . 
     As noted previously, the configurations in  FIGS. 3A-3B  have the control lines  120 A-B pass through the wellhead  115  using known techniques. For the configuration in  FIG. 3C , however, the balance control line  120 B is terminated downhole with a cap  130  using capping techniques known in the art. The depth at which the balance control line  120 B is capped can vary depending on the implementation. In practice, the balance control line  120 B is intended to provide an offset of the hydrostatic pressure in the primary control line  120 A. 
     When deploying the control system  100  of  FIG. 3C  downhole, the balance control line  120 B is preferably evacuated of hydraulic fluid. As the lines  120 A-B are lowered with the tubing  20 , the primary control line  120 A bleeds hydraulic pressure into the balance control line  120 B through the regulator  150 , which allows pressure flow from the line  120 A to  120 B (but not from  120 B to  120 A). As hydraulic pressure builds in the balance line  120 B, an amount of trapped gas forms in the line  120 B, which is beneficial for the operation of the control system  100 . For example, this trapped gas acts as a compressible buffer and can help avoid vapor lock in the system  100 . 
     In any of the configurations of  FIGS. 3A-3C , if the balance control line  120 B line is ever lost, the regulator  150  can bleed hydraulic pressure from the primary line  120 A to the balance control line  120 B to achieve any of the various purposes disclosed herein. Details of the regulator  150  for the control system  100  are shown in  FIGS. 5A-5B . 
     The regulator  150  is shown in a closed condition in  FIG. 5A  and is shown in an opened condition in  FIG. 5B . As shown, the regulator  150  has a housing  160  defining an internal passage therein so that this arrangement represents the regulator  150  designed as a separate component from the safety valve ( 50 ). However, as noted previously, it will be appreciated that the regulator  150  can be part of the safety valve ( 50 ) and the regulator&#39;s housing  160  can actually be components of the safety valve ( 50 ) itself. Moreover, the housing  160  can be constructed in ways known in the art for facilitating its assembly, which may not be depicted in the drawings. 
     The housing  160  has a primary port  162  with a hydraulic fitting  163  for connecting to the primary control line  120 A with a flow tee or the like. The primary port  162  communicates with an intermediate barrel chamber  166  through a choke passage  164 . A sleeve  170  installs in the intermediate barrel chamber  166  and has a hydraulic fitting  173  for connecting to the balance control line  120 B with a flow tee or the like. 
     A dart  190  for flow control resides in the primary port  162  and can move therein to seal against a seal or seat  165  around the choke passage  164 . A piston  180  resides in the open end  174  of the sleeve  170 . A spring  185  resides in an atmospheric or low pressure chamber of the sleeve  170  behind the piston  180  and biases the piston  180  outward. Depending on the hydraulic pressure acting against the piston&#39;s front end  182  and the bias of the spring  185 , the piston  180  can move relative to the dart  190  and can push the dart  190  relative to the choke passage  164 . 
     As noted previously, hydraulic pressure applied to the primary control line  120 A (communicating with port  162 ) opens the safety valve ( 50 ) coupled to the lines  120 A-B. Hydraulic pressure from control line  120 A applied to the balance control line  120 B until the balance line reaches its designed hydrostatic pressure. At that pressure, the communication between line  120 A to line  120 B will cease. The stored hydrostatic pressure in line  120 B acts to offset the hydrostatic pressure from the primary control line  120 A for the purposes of controlling the safety valve ( 50 ) as disclosed herein. 
     In the closed condition of  FIG. 5A , the hydraulic pressure of the primary control line  120 A pushes against the dart  190  so that it seals on the seat  165  inside the choke passage  164 . On the other end of the regulator  150 , hydraulic pressure from the balance control line  120 B pushes the piston  180  against the bias of spring  185  so that the piston  180  does not engage the dart  190 . In particular, pressure from the balance control line  120 B communicates through the fitting  173  and passes out the sleeve&#39;s cross-ports  172  to communicate in the annulus around the sleeve  170  in the barrel chamber  166 . 
     The pressure communicates to the end  174  of the sleeve  170  and enters the space between the dart  190  and the piston  180 . Here, the hydraulic pressure acts against the piston&#39;s end  182  having a cup seal  184 , and the pressure tends to force the piston  180  against the bias of the spring  185 . The cup seal  184  can use non-elastomeric, metal-to-metal sealing systems known in the art, although any suitable sealing system could be used. 
     At normal conditions, the primary pressure in port  162  acting against the dart  190  is greater to or equal to the second pressure in chamber  166  acting against the dart  190  so that the dart  190  seals off flow through the regulator  150 . In other words, the differential between the first and second hydraulic pressures bias the piston  182  to the released position as shown in  FIG. 5A , thus allowing the dart  190  to be in the closed condition. If the balance control line  120 B loses integrity and insufficient annular pressure is present to offset the primary control line&#39;s hydrostatic pressure, then the safety valve ( 50 ) as described previously can fail in the open position, which is unacceptable. 
     Weakening of the pressure integrity of the balance control line  120 B is shown in  FIG. 5B . Reduced pressure acting against the piston  180  has allowed the spring  185  to bias the piston  180  so that it now engages the end of the dart  190 . If the weakening is great enough, then the piston  180  pushes the dart  190  through the choke passage  164  and away from the seal  165  as shown. (Preferably, the cup seal  184  on the piston&#39;s end  182  is not allowed to pass the edge  174  of the sleeve  170  because this could damage the seal  184  and cause it to extrude.) 
     Having the dart  190  moved away from the seal  165  allows pressure from the primary control line  120 A to pass by the dart  190  and through choke passage  164 . This action bleeds pressure from the primary control line  120 A to the balance control line  120 B. In this way, the regulator  150  helps the control system  100  to overcome failure of the safety valve ( 50 ) in the opened condition. 
     By opening as in  FIG. 5B , for example, the regulator  150  ensures that the primary control line  120 A at port  162  bleeds into balance line  120 B, thus equalizing the hydrostatics to the safety valve ( 50 ). As hydraulic pressure bleeds through the regulator  150 , the hydraulic pressure supplied by the primary line  120 A to the safety valve ( 50 ) may fall below a level that allows the safety valve ( 50 ) to remain open. For instance, the force from the internal spring ( 56 ) in the valve ( 50 ), any remaining pressure in the balance control line  120 B, and possibly tubing pressure, if applicable, can act to close the valve ( 50 ) as described previously. When this happens, the safety valve ( 50 ) closes and fails in the closed condition rather than staying open. 
     If integrity in the balance control line  120 B is regained, then the hydraulic pressure in the balance line  120 B can eventually move the piston  180  against the spring  185  and allow the dart  190  to seat in the closed position of  FIG. 5A . Once this is done, the primary control line  120 A can again be used to operate the valve ( 50 ) while the balance control line  120 B provides the hydrostatic offset for deep-set operation. 
     For ease of explanation, the disclosed control system has been described generally in relation to a cased vertical wellbore. However, the disclosed control system can be employed in any type of well, such as an open wellbore, a horizontal wellbore, or a diverging wellbore, without departing from principles of the present disclosure. Furthermore, a land well is shown for the purpose of illustration; however, it is understood that the disclosed control system can also be employed in offshore wells. 
     Spring forces, hydraulic surface areas, volumes, and other details for the components disclosed herein can be suited for a particular implementation and can vary based on expected operating pressures and other considerations. Therefore, the disclosed regulator and control system can be configured to operate in response to a set and determined pressure differential for a particular implementation. With that said, the disclosed regulator and control system are intended to permit hydraulic pressure to flow from a primary control line to a balance line in response to pressure in the balance line falling below some set pressure level. In general, this set pressure level is related to the hydrostatic pressure associated with the column of hydraulic fluid in the primary control line, although the actual values of the level may be different than the precise hydrostatic pressure. 
     Although use of one regulator  150  between control lines  120 A-B has been shown and described herein, it will be appreciated that multiple regulators  150  can be used between the control lines  120 A-B. These multiple regulators  150  can be similarly configured to provide redundancy should one fail to operate. Alternatively, the various regulators  150  can be configured to operate differently in response to different hydraulic pressures in the control lines  120 A-B, which in turn can have direct bearing on the safety valve&#39;s operation and the pressures it is exposed to. 
     Again, although the disclosed regulator  150  of  FIGS. 5A-5B  is shown as a separate component with its own housing  160 , it will be appreciated that the regulator  150  can be incorporated into the housing of the safety valve  50  as shown in  FIG. 4B  or incorporated into some other downhole tubing component. For example, the control lines  120 A-B can communicate with internal channels or ports that connect to an internal chamber in the safety valve&#39;s housing. Components of the regulator  150 , such as sleeve  170 , piston  180 , spring  185 , and dart  190  can install in the valve&#39;s internal chamber to regulate hydraulic pressure between the ports for the control lines  120 A-B according to the purposes disclosed herein. 
     The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.