Patent Publication Number: US-2016238156-A1

Title: Pump valve seal with abrasion gauge

Description:
FIELD 
     This disclosure relates generally to fluid delivery systems and more particularly to valve assemblies delivering particulate-containing fluids. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     It is common to pump fluids that contain particulates into oil and gas wells. For example, fracturing fluids typically contain proppant particles, such as sand, synthetic particles or small beads, with sizes typically from U.S. Standard Sieve sizes 10 through 60. Reciprocating plunger pumps are frequently used to create the high-pressure fluid flow needed to inject fluids, such as fracturing fluids, into oil and gas formations. These pumps typically include valve assemblies that are biased toward the closed position. When the motion of the plunger creates a differential pressure across the valve, the differential pressure forces the valve open, allowing the fluid to flow through the valve. However, solid particles in the fluid can become trapped within the valve assembly upon valve body, allowing extrusion or damage to valve assembly components and reducing the useful life of the valve assembly. 
     Valves used for slurry service typically have a resilient sealing insert around the outer perimeter of the valve body member to provide effective valve sealing. Pressure applied to a closed valve forces the resilient sealing insert to become a hydraulic seal and a portion of the insert is extruded into the gap between the valve body member and the valve seat member. For the insert to affect a hydraulic seal upon valve closure, the insert must protrude from the valve body member toward the valve seat member when the valve is open. The amount of protrusion of the insert is called the insert standoff. When the valve is nearly closed, the resilient sealing insert contacts the valve seat member before the contact surfaces of the valve body member and the valve seat member make contact. When the valve is closed, the resilient sealing insert is deformed against the seat member to form the hydraulic seal, and metal-to-metal contact occurs between the valve body member and the valve seat member in the strike face area. The insert material does not compress, but rather deforms. Repeated deformation of the insert material causes internal heat build-up and material stress within the insert material, and this can damage it. Combined with repeated deformation and presence of hard particles, such as sand or other proppant materials, extrusion and cyclic fatigue of the insert material can occur, and potential lead to further valve or pump damage and/or failure. 
     Also, conventional liquid end valve assemblies may also experience failures due to foreign objects becoming lodged within the valve assembly (e.g., bolts or gravel can accidentally enter the fluid flow path). These foreign objects can become wedged between the contact surfaces of the valve, and thus prevent the valve from closing, and damaging the sealing inserts. In an operational setting, continual inspection and maintenance efforts are made to detect damage to, and erosion of, the sealing inserts. However, making a decision to replace valves due to sealing insert damage and erosion can often be a subjective or difficult evaluation. This can often lead to unnecessary replacement and use of resources, or even damage to valves and/or pumps. 
     There is a need for improved valve assemblies which improve or overcome difficulties in assessing damage to, and erosion of, the sealing inserts, and such need is addressed, at least in part, by embodiments described in the following disclosure. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a necessarily a comprehensive disclosure of its full scope or all of its features. 
     In a first aspect of the disclosure, a valve element includes a valve body member formed of a rigid material, where the valve body member defines a front-to-rear extending longitudinal axis, and has a generally radially outwardly facing first contact surface of generally frusto-conical configuration tapering forwardly, and a radially inwardly extending annular recess disposed rearwardly of the contact surface. The valve body member further has a sealing insert mounted on the valve body member which includes a generally radially inwardly projecting lip received in the recess, an axially forwardly facing sealing face, a radially inwardly facing second contact surface disposed between the sealing face and the lip which tightly engages the first contact surface to conform to the frusto-conical configuration thereof, and a seal abrasion gauge disposed upon an outer peripheral portion of the axially forwardly facing sealing face. In some aspects, the seal abrasion gauge may be integrated with or otherwise disposed within the sealing insert. In some other aspects, the seal abrasion gauge is an insert disposed adjacent an outer peripheral portion of the axially forwardly facing sealing face and a radially outwardly facing third contact surface disposed upon an opposing side of the sealing insert relative the second contact surface. In some embodiments, the seal abrasion gauge has a color in contrast with a color of the sealing insert, and may be formed from a colorant infusion in the sealing insert. 
     In another embodiment of the disclosure, a valve element is provided which includes a valve body member formed of a rigid material, where the valve body member defines a front-to-rear extending longitudinal axis. The valve body member also has a generally radially outwardly facing first contact surface of generally frusto-conical configuration tapering forwardly, and a radially inwardly extending annular recess disposed rearwardly of the contact surface. The valve body member further has a sealing insert mounted on the valve body member which includes a generally radially inwardly projecting lip received in the recess, an axially forwardly facing sealing face, a radially inwardly facing second contact surface disposed between the sealing face and the lip which tightly engages the first contact surface to conform to the frusto-conical configuration thereof, and a seal abrasion gauge integrated with an outer peripheral portion of the axially forwardly facing sealing face. In some cases, the seal abrasion gauge is an insert disposed adjacent an outer peripheral portion of the axially forwardly facing sealing face and a radially outwardly facing third contact surface disposed upon an opposing side of the sealing insert relative the second contact surface, while in other cases the seal abrasion gauge is integrated with the sealing insert. The seal abrasion gauge may have a color in contrast with a color of the sealing insert. 
     Yet another aspect of the disclosure is a valve element having a valve body member formed of a rigid material, and the valve body member defines a front-to-rear extending longitudinal axis. The valve body member also has a generally radially outwardly facing first contact surface of generally frusto-conical configuration tapering forwardly, and a radially inwardly extending annular recess disposed rearwardly of the contact surface. The valve body member further includes a sealing insert mounted on the valve body member which includes a generally radially inwardly projecting lip received in the recess, an axially forwardly facing sealing face, a radially inwardly facing second contact surface disposed between the sealing face and the lip which tightly engages the first contact surface to conform to the frusto-conical configuration thereof, and a radially outwardly facing third contact surface disposed upon an opposing side of the sealing insert relative the second contact surface. A seal abrasion gauge is disposed adjacent the third contact surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the disclosure will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figures illustrate the various implementations described and are not meant to limit the scope of various technologies described herein, and: 
         FIG. 1  illustrates a high pressure pump which includes valve elements, in a cross-sectional view; 
         FIG. 2  depicts a valve element showing erosion of sealing insert in accordance with the disclosure, and in a perspective view; 
         FIGS. 3A and 3B  illustrates a valve element having an abrasion gauge in accordance with an aspect of the disclosure, in a cross-sectional view; 
         FIG. 4  depicts a valve element which includes another variation of a seal abrasion gauge in accordance with the disclosure, and in a cross-sectional view; 
         FIG. 5  illustrates another valve element in accordance with some aspects of the disclosure, and in a cross-sectional view; and, 
         FIG. 6  depicts yet another valve element according to an aspect of the disclosure, in a cross-sectional view. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the variations is merely illustrative in nature and is in no way intended to limit the scope of the disclosure, its application, or uses. The description and examples are presented herein solely for the purpose of illustrating the various embodiments of the disclosure and should not be construed as a limitation to the scope and applicability of the disclosure. 
     Unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
     In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of concepts according to the disclosure. This description should be read to include one or at least one and the singular also includes the plural unless otherwise stated. 
     The terminology and phraseology used herein is for descriptive purposes and should not be construed as limiting in scope. Language such as “including,” “comprising,” “having,” “containing,” or “involving,” and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited. 
     Also, as used herein any references to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily referring to the same embodiment. 
     Referring to  FIG. 1 , a high pressure pump such as a plunger pump includes valve elements, shown generally as  100  (discharge valve) and  100   a  (suction valve). The valve elements  100  and  100   a  fit in the pump body  102 , which forms a intake chamber  104 , compression chamber  105 , and a discharge chamber  106 . Annular walls  108  in the pump body  102  provide structures for receiving valve seat members  120 . Valve seat member  120  comprises a hollow bore  122  that provides a fluid flow path between the compression chamber  105  and the discharge chamber  106 , or the compression chamber  105  and the intake chamber  104 . Valve seat member  120  has a frusto-conical contact surface  124  and a generally cylindrical inner wall  126  that defines the valve seat member bore  122 , and which can act as a guide surface. Valve body member  130  has a frusto-conical contact surface  132  that is complimentary to the frusto-conical contact surface  124  on the valve seat member  120 . A compression spring  134  urges valve body member  130  toward the valve seat member  120  to create a contacting relationship between frusto-conical contact surface  124  and frusto-conical contact surface  132 . 
     In operation, the discharge stroke of the plunger  140  results in an elevated pressure within the compression chamber  105 . The elevated pressure within the compression chamber  105  causes the valve body member  130  of discharge valve  100  to move away from the valve seat member  120  as shown by the arrow  146 . This allows fluid to be displaced from the compression chamber  105 , through the valve seat member bore  122 , and into the discharge chamber  106 . Fluid flow from the compression chamber  105  into the discharge chamber  106  is referred to as forward flow through the valve apparatus  100 . When valve body member  130  of discharge valve  100  is raised by fluid forces arising from the forward motion of the plunger  140 , the compression spring  134  is compressed and exerts an increasing force downward on the valve body member  130 . When the plunger  140  slows towards the end of its discharge stroke, the fluid forces upward on the valve body member  130  decrease and become less than the spring force downward on the valve body member  130 . The valve body member  130  is pushed downwards towards its closed position against the valve seat member  120 . The compression spring  134  moves the valve body member  130  towards the valve seat member  120  to reestablish the contacting relationship between frusto-conical contact surface  124  and frusto-conical contact surface  132 . Further movement of the plunger  140  in a suction stroke will create a suction within the intake chamber  104  and the suction valve assembly  100   a  will work in a similar manner, allowing fluid to be drawn into the intake chamber  104  and compression chamber  105 . At the start of the plunger  140  suction stroke, a small amount of fluid flows from the discharge chamber  106  into the suction chamber  104 . This is referred to as reverse flow through the valve apparatus  100 . This reverse flow will continue until the combined forces of the suction pressure within the intake chamber  104  and the compression spring  134  are sufficient to form a positive seal between the valve body member  130  and the valve seat member  120  of suction valve assembly  100   a.    
     Forward flow and reverse flow through the valve apparatus  100  have separate working mechanisms and are not equivalent. Forward flow results when the pressure in the intake chamber  104  is sufficiently greater than the pressure in the discharge chamber  106  that it overcomes the resistance force applied by the compression springs  134 . Forward flow involves hydrostatic pressure overcoming a resisting force. Reverse flow also needs a pressure differential across the valve assembly  100   a.  But rather than the pressure differential overcoming an opposing force, reverse flow involves the time lag inherent in the valve body member  130  of valve assembly  100   a  closing. Once the pressure has equalized between the intake chamber  104  and the discharge chamber  106 , the forward flow of fluid will stop. At that time the valve body member  130  of valve assembly  100   a  will still be in the process of approaching the valve seat member  120 , moving in response to the force from the compression spring  134 . The time period between the cessation of the forward fluid flow and the closing of the valve body member  130  upon the valve seat member  120  is commonly referred to as valve lag. During this valve lag time period the start of the plunger suction stroke has reduced the pressure within the intake chamber  104  to less than the discharge chamber  106 . This results in a reverse fluid flow until there is an adequate fluid seal between the valve body member  130  of valve assembly  100   a  and the valve seat member  120 . If an adequate fluid seal between the valve body member  130  and the valve seat member  120  is not achieved, there will be reverse fluid flow throughout the entire suction stroke, and pumping efficiency may be significantly diminished. 
     A sealing insert  136  is attached to the valve body members  130  at the outer perimeter that acts to help effectuate a seal between frusto-conical contact surface  124  and frusto-conical contact surface  132 . The distance between the sealing insert  136  and the opposing frusto-conical contact surface creates a valve exit gap  138 . The sealing insert also acts to dampen the stress forces imposed on the valve seat member  120  and the valve body member  130  upon valve closure. For the sealing insert  136  to be effective, the valve exit gap  138  between the sealing insert  136  and the valve seat contact surface  124  must be smaller than the gap between the valve body member contact surface  132  and the valve seat contact surface  124 , when the valve is open. 
     A common problem often occurs within pump assemblies that are used to pump solid laden fluids or slurries, such as hydraulic fracturing fluid containing proppant particles. As the valve body member  130  approaches the valve seat member  120 , the resilient insert  136  approaches the opposing frusto-conical contact surface  124  and the valve exit gap  138  decreases. When the valve exit gap  138  reaches a certain point (for example, about 1.0-2.5 times the average solid particle diameter), the valve exit gap  138  will act to screen out the solid particles while still allowing fluid flow to pass. This forward screening effect will result in an accumulation of solid particles  144  (sixteen shown) between the valve seat member  120  and the valve body member  130 . As the valve body member  130  closes against the valve seat member  120 , the accumulation of solid particles  144  imposes localized forces onto the valve assembly. These localized forces can result in damage to the valve seat member  120 , the valve body member  130  or the resilient insert  136 , such as pitting or erosion on one or more of the frusto-conical contacting surfaces or resilient insert. Hence, in an operational setting, continual inspection and maintenance efforts are thus required to detect damage to, deformation of, and erosion of, the resilient sealing inserts  136 . In some cases where sealing inserts  136  significantly erode or fail, crushing of individual particles may result in Hertzian contact stresses and damage to the frusto-conical contact surfaces  124  and/or  132 . 
       FIG. 2  illustrates valve element  100  in a perspective view, and inverted orientation, showing erosion of sealing insert  136 . As illustrated, valve element  100  includes sealing insert  136  disposed on the periphery of valve body member  130 , and includes an axially forwardly facing sealing face. Sealing insert  136  is seated adjacent frusto-conical contact surface  132 . As described above, when valve body member  130  closes against a valve seat member, the accumulation and contact of solid particles can result in damage to the axially forwardly facing sealing face of sealing insert  136 . Such damage is shown as erosion  146  occurring in the portion of sealing insert  136  adjacent frusto-conical contact surface  132 . 
     Now referring to  FIG. 3A , which illustrates valve element  300  in a cross-sectional view. The valve element  300  may generally fit in a pump body, such as pump body  102  of  FIG. 1  forming an intake or pressure chamber  104 , compression chamber  105 , and/or discharge chamber  106 , and which includes valve seat member  120 . Valve element  300  further includes valve body member  330  and sealing insert  336  disposed on the valve body member  330 , which helps effectuate a seal between frusto-conical contact surface  332  and a frusto-conical contact surface of a valve seat member, such as valve seat members  124  in  FIG. 1 . Valve body member  330  may be formed of a rigid material, such as metal. Sealing insert  336  is mounted on valve body member  330  in the form of an annular ring-shaped insert formed of an elastomeric material such as urethane or rubber, or any other sealingly resilient material, for example. In some cases, the sealing insert  336  is mounted onto the valve body member  330  by being stretched and slid axially over the front end of the body (i.e., over the lower end thereof as viewed in  FIG. 3A ) before being released to snap into an annular groove  356  of valve body member  330 . In that fashion, a radially inwardly projecting annular lip  358  of the sealing insert  336  enters a radially inwardly recessed annular portion  360  of the groove  356 , and an inner contact surface  362  of sealing insert  336  tightly engages an outer contact surface  364  of valve body member  330 . In other aspects, the sealing insert  336  can be manufactured in place on the valve body member  330 . 
     Sealing insert  336  further includes a peripheral contact surface  366 , and axially forwardly facing sealing face  376 . In some aspects of the disclosure, sealing insert  336 , or any sealing insert according to the disclosure, is formed of a material and/or contains additives with anti-extrusion properties to reduce or even prevent sealing insert material extrusion into the gap, such as exit gap  138  shown in  FIG. 1 . A seal abrasion gauge  370  disposed adjacent to and tightly engages the contact surface  366  of sealing insert  336 . Seal abrasion gauge  370  is also disposed within annular groove  356 , and is tightly engaged with contact surface  372  of valve body member  330 . Similar to sealing insert  336 , seal abrasion gauge  370  is mounted on valve body member  330  in the form of an annular ring-shaped insert. Seal abrasion gauge  370  includes a frusto-conical shaped contact surface  374  which may further effectuate a seal between frusto-conical contact surface  332  and a frusto-conical contact surface of a valve seat member. 
     Now referencing  FIG. 3B , in operation when valve body member  330  closes against a valve seat member (such as seat member  124 ), accumulation of, and/or contact with, solid particles  380  laden in pumped fluid occurs, which in turn damages the axially forwardly facing sealing face  376   a  of sealing insert  336 . Over a period of use, erosion to the sealing face  376   a  of sealing insert  336  gradually migrates in an outward path, beginning at a lower edge of contact surface  364  and continuing to a lower edge of peripheral contact surface  366  of sealing insert  336 . Once the erosion has reached the lower edge of inner contact surface  366  of seal abrasion gauge  370 , it may become readily observable that valve element  300  may need replacement, repair, or maintenance. In some aspects, the observable indication may be presented visually, color, by raised ridge, or contour difference between surface  374  and eroded surface  376   a,  or combination thereof. In some aspects where an indication of sealing face  376   a  erosion is detected visually, sealing insert  336  may have a first color, while seal abrasion gauge  370  has a second color in at least adequate contrast with the first color, such that an observer may visually ascertain erosion has reached the lower edge of inner contact surface  366 . In yet other aspects where a visual indication of sealing face  376   a  erosion is used, a difference in contour or surface shape between surface  374  and eroded surface  376   a  is observable. In some other instances, the difference in contour or surface shape between surface  374  and eroded surface  376   a  may be detected by touch. 
       FIG. 4  illustrates valve element  400  in a cross-sectional view, which includes another variation of a seal abrasion gauge, in accordance with some other embodiments of the disclosure. The valve element  400  includes valve body member  430  and sealing insert  436  disposed on the valve body member  430 . Seal abrasion gauge  470  is disposed outwardly adjacent sealing insert  436 . Sealing insert  436  and seal abrasion gauge  470  are mounted on valve body member  430  in the form of annular ring-shaped structures, and may be preassembled prior to mounting on valve body member  430 . The sealing insert  436  and seal abrasion gauge  470  are mounted onto the valve body member  430  by being stretched and slid axially over the front end of the valve body member  430  before being released to snap into an annular groove  456  of valve body member  430 . Both of the insert  436  and gauge  470  are secured within groove  456  in similar fashion as described above for  FIG. 3 , where sealing insert  436  tightly engages an outer contact surface  464  of valve body member  430 . Seal abrasion gauge  470  further includes inwardly projecting annular lip  478  in tight contact with valve body member  430 , and inwardly projecting annular lip  458  of sealing insert  436 . 
       FIG. 5  depicts another valve element in a cross-sectional view in accordance with yet other embodiments of the disclosure. Valve element  500  is similar to valve element  300  shown in  FIG. 3  and further includes a raised feature disposed on contact surface  580  of seal abrasion gauge  570 . Seal abrasion gauge  570  is disposed outwardly adjacent sealing insert  536 , both of which securely in contact with valve body member  530 . The raised feature extends above a plane upon which axially forwardly facing sealing face  576  of sealing insert  536  falls. The extent of erosion of sealing face  576  may be detected and evaluated by reference to the raised feature on surface  580 . The raised feature may be a continuous ring formed around the circumference of surface  580  in some cases, while in other aspects, the raised feature may be intermittently disposed thereon, such as a bump, nib, partial ridge, and the like. In some cases, the raised feature is wearable. 
     Another embodiment of a valve element in accordance with the disclosure is shown in  FIG. 6 , in a cross-sectional view. Valve element  600  includes sealing insert  636  with seal abrasion gauge  682  disposed upon an outer peripheral portion of the axially forwardly facing sealing face  676 . Seal abrasion gauge  682  may be formed material different than the material forming sealing insert  636 , and fused within the sealing insert  636 . In some other aspects, seal abrasion gauge  682  may be a colorant infused into the sealing insert  636 , having a color with adequate visual contrast with the color of sealing insert  636 . 
     The components of the valve elements in accordance with the disclosure may be made from a variety of materials depending on design factors such as the type of fluid to be pumped and the pressure rating that is needed. For example, the pump body portion  102  and the valve seat member  120 , shown in  FIG. 1 , may be made of metal. The valve body members also, may be made of metal but could also be made from composites or other durable materials in an effort to control the weight and balance of the valve body members. The frusto-conical contact surfaces, such as  124  and  132 , are typically made from a durable metal, while the sealing inserts are usually made from an elastomeric deformable material such as polyurethane, or any suitable thermoset or thermoplastic elastomer, such as, but not necessarily limited to, natural polyisoprene, synthetic polyisoprene, polybutadiene, chloropene, butyl rubber, halogenated butyl rubbers styrene-butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, ethylene propylene rubber, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber, fluoroelastomers, perfluoroelastomers, polyether block amides, chlorosulfonated polyethylene, ethylene-vinyl acetate, polyaryletherketone, polyetheretherketone, combinations thereof, and the like. This material may be selected based upon properties of elasticity and capability for surviving large repeated deformations and/or impacts. In some aspects, such materials are softer and more pliable elastomers. In some other aspects, two or more different elastomeric materials (e.g., two different polyurethanes with appropriate properties) make up the sealing insert. 
     Materials used to form seal abrasion gauge according to the disclosure may in some cases be like materials as those used to form the sealing inserts, and in some other instances, materials different from those used to form the sealing inserts. When different materials are used, they are generally more abrasion or wear resistant than the sealing insert material. Such material may be selected based upon properties of abrasion resistance and capability for surviving large repeated deformations, and may include materials such as polyurethane, polyamide, polyacetal, polytetrafluorethylene, epoxies, polyimide, polycarbonate, polyethylene, polypropylene, polydimethylsiloxane, or any suitable thermoset or thermoplastic polymers, combinations thereof, and the like. In some aspects, the material may be further amended with other components to achieve targeted properties, such as aramid fiber, carbon fiber, graphite powder, glass fiber, molybdenum disulfide particles, and the like. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. Example embodiments are provided so that this disclosure will be sufficiently thorough, and will convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the disclosure, but are not intended to be exhaustive or to limit the disclosure. It will be appreciated that it is within the scope of the disclosure that individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
     Also, in some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. Further, it will be readily apparent to those of skill in the art that in the design, manufacture, and operation of apparatus to achieve that described in the disclosure, variations in apparatus design, construction, condition, erosion of components, gaps between components may present, for example. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     Although a few embodiments of the disclosure have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.