Abstract:
Methods and apparatus for sealing a check valve. The check valve includes a closure member, primary and secondary sealing elements, and a spring that urges the closure member into engagement with the primary sealing element. The primary sealing element is retained by a groove formed by the housing and the second sealing elements. Increasing pressure acting on the closure member compresses the primary sealing element and allows the closure member to engage the secondary sealing element. As it compresses, the primary sealing element wipes contamination from the closure member to provide a clean sealing surface for engagement with the secondary sealing element. The secondary sealing element also provides sealing redundancy, which is especially beneficial in gas sealing applications.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of 35 U.S.C. 111(b) provisional application Ser. No. 60/529,30 filed Dec. 12, 2003, and entitled “Check Valve Sealing Arrangement.” 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable.  
       FIELD OF THE INVENTION  
       [0003]     The present invention relates generally to seals for check valves. More particularly, the present invention relates to sealing systems for check valves.  
       BACKGROUND  
       [0004]     Check valves are unidirectional valves that allow fluid flow in only one direction. Many check valves are considered direct-acting such that the valve is actuated by the application of flowing fluids to the valve. Many of these direct-acting check valves have a closure member that is held in a sealed position by a spring. The valve remains sealed until the fluid pressure on one side of the valve overcomes the force of the spring and moves the closure member. When the flow of fluid is reversed, the fluid pressure, in conjunction with the force of the spring, maintains the closure member in the sealed position. Check valves are commonly used in pumps, control systems, and other applications where a particular fluid path may be subjected to alternating flows.  
         [0005]     Modern formation test tools utilize downhole pumps to remove drilling mud and mud filtrate from isolated zones of interest. These downhole pumps use direct-acting check valves to control the direction of fluid entering and exiting the chambers of reciprocating piston-style pump (see  FIG. 5 ). The fluids encountered during the downhole pumping operations are often a mixture of drilling fluids, formation fluids (oil, water or gas), and solid formation materials, such as sand. Sand, and other solid materials, in the fluid can cause the check valves to become fouled, preventing a reliable sealing engagement. Without a reliable seal, the check valve is rendered ineffective to perform the required pumping operations.  
         [0006]     Other flow control applications that involve fluids with debris or other contaminants may also utilize check valves. For example, mining applications, machine tool cutting fluid circulation systems, and automotive applications, including engine oil systems. These systems and applications are also susceptible to reliability issues with check valves operating in dirty, or contaminated, environments.  
         [0007]     Therefore, a check valve design having improved sand and debris tolerance is desirable. Accordingly, there remains a need to develop improved check valve systems, which overcome certain of the foregoing difficulties while providing more advantageous overall results.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0008]     The embodiments of the present invention are directed to methods and apparatus for sealing a check valve. The check valve includes a closure member, primary and secondary sealing elements, and a spring that urges the closure member into engagement with the primary sealing element. The primary sealing element is retained by a groove formed by the housing and the second sealing elements. Increasing pressure acting on the closure member compresses the primary sealing element and allows the closure member to engage the secondary sealing element. As it compresses, the primary sealing element wipes debris from the closure member.  
         [0009]     In one embodiment, a check valve comprises a body having first and second ports. An insert is disposed within the body and in fluid communication with both the first and second ports. A closure member is disposed within the insert. A first sealing element is disposed circumferentially about the second port and a second sealing element is disposed adjacent to the first sealing element, wherein the second sealing element forms at least a portion of a groove retaining the first sealing element. A spring is adapted to urge the closure member into engagement with the first sealing element. The closure member has a first sealing position, in which the closure member is sealingly engaged with the first sealing element, and a second sealing position, in which the first sealing element is substantially compressed within the groove and the closure member is sealingly engaged with the second sealing element. In the second sealing position, the first sealing element wipes debris from the closure member.  
         [0010]     In an alternate embodiment, a valve assembly comprises a body having first and second ports. A closure member and a primary sealing element are disposed within the body. The assembly also comprises a spring adapted to urge the closure member into sealing engagement with the primary sealing element so as to isolate the first port from the second port. The assembly also comprises a secondary sealing element disposed within the body so as to sealingly engage the closure member as pressure in the first port compresses the closure member against the primary sealing element.  
         [0011]     Thus, the present invention comprises a combination of features and advantages that enable it to overcome various shortcomings of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:  
         [0013]      FIG. 1  is a cross-sectional view of a prior art check valve;  
         [0014]      FIG. 2  is a cross-sectional view of one embodiment of a check valve in accordance with embodiments of the present invention;  
         [0015]      FIG. 3  is a cross-sectional view of the check valve of  FIG. 2 , shown in an open position;  
         [0016]      FIG. 4  is a cross-sectional view of the check valve of  FIG. 2 , shown in a closed position;  
         [0017]      FIG. 5  is a cross-sectional view of a pump assembly including check valves constructed in accordance with embodiments of the present invention;  
         [0018]      FIG. 6  is a schematic view of a downhole tool pumping section including check valves constructed in accordance with embodiments of the present invention; and  
         [0019]      FIG. 7  is a schematic view of a downhole formation testing tool including the pumping section of  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results.  
         [0021]     In particular, various embodiments described herein thus comprise a combination of features and advantages that overcome some of the deficiencies or shortcomings of prior art check valve apparatus or systems. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of preferred embodiments, and by referring to the accompanying drawings.  
         [0022]     Referring to  FIG. 1 , a conventional check valve assembly  10  is shown. Assembly  10  includes valve body  12  having two ports  14  and  16 , threaded insert  18 , spring  20 , closure member  22 , sealing element  24 , seat retainer  26 , and static seals  28 . Spring  20  urges closure member  22  into initial sealing engagement with the sealing element  24 . Closure member  20  is shown as a ball-type closure member. Sealing element  24  is commonly an elastomeric seal, such as an O-ring. Sealing element  24  is captured between seat retainer  26  and threaded insert  18 , which prevents dislodgment of the seal during flow reversal.  
         [0023]     As fluid pressure is increased in the “checked” direction  30 , closure member  22  is further forced into the sealing element  24  until the closure member physically contacts seat retainer  26 . Sealing engagement is provided by sealing element  24  being compressed between closure member  22  and seat retainer  26 . In the reversed flow, or “un-checked” direction  32 , the fluid pressure compresses spring  20  to push closure member  22  away from sealing element  24 , and to provide a relatively unrestricted flow path. The pressure required to unseat closure member  22  from sealing element  24 , thus permitting flow in the un-checked direction, is called the “cracking” pressure.  
         [0024]     As previously discussed, one problem with seal assembly  10  is that, in the presence of solid particles or sand in the fluid while flowing in the un-checked direction, particles tend to build up in between closure member  22  and sealing element  24 . Upon flow reversal to the checked direction  30 , the built up particles prohibit closure member  22  from making adequate sealing engagement with sealing element  24 . Increased spring force has been utilized to further “force” closure member  22  through the debris and into proper contact with sealing element  24 . Although this increased spring force is effective in improving the sealability of valve assembly  10 , the increased spring force increases the “cracking” pressure of the valve. The higher cracking pressure creates high localized flow velocities through the region in between closure member  22  and sealing element  24 , which accelerates erosion of the elastomeric sealing element and the closure member.  
         [0025]      FIG. 2  illustrates one embodiment of a check valve assembly  100  comprising valve body  102  having checked flow port  104  and free flow port  106 . Assembly  100  also comprises, threaded insert  108 , spring  110 , closure member  112 , primary sealing element  114 , secondary sealing element  116 , seat retainer  118 , and static seals  120 . Closure member  112  may be a ball, hemisphere, or other type of shaped closure member. Threaded insert  108  engages body  102  to hold spring  110  in place against closure member  112 .  
         [0026]     As shown in  FIG. 2 , in the presence of zero flow, or balanced pressure across closure member  112 , spring  110  urges closure member  112  into initial sealing engagement with the primary sealing element  114 . Primary sealing element  114  is disposed within groove  126  formed between threaded insert  108  and secondary sealing element  116 , which is supported by seat retainer  118 . In certain embodiments, primary sealing element  114  has a circular cross-section sized so as to be retained in groove  126  formed between a triangular cross-sectioned secondary sealing element  116  and the base of threaded insert  108 . Groove  126  may be a dove-tailed groove or some other shape to effectively trap primary sealing element  114  to prevent it from becoming dislodged during flow reversals.  
         [0027]     Primary sealing element  114  may have any cross-sectional shape or arrangement of shapes that is suitable for a particular application. For example, sealing element  114  may have square, oval, faceted, chevron, or other shaped surfaces and cross-sections. Sealing element  114  may also be a bonded seal comprising a resilient member bonded to another less-resilient member.  
         [0028]     Primary sealing element  114  is preferably a compliant, flexible seal, such as an elastomeric O-ring type seal. Materials such as urethane, natural rubber, nitrile rubber, fluorocarbons (Viton®), and perfluoro-elastomers (Kalrez®) may be suitable for use as primary sealing element  114 . Secondary sealing element  116  is preferably a polymeric sealing element that is less compliant that primary sealing element  114  and has a cross-section that acts with threaded insert  108  to form groove  126 . Secondary sealing element  116  may be constructed from a material such as polyetheretherketone (PEEK), Polytetraflouroethylene (Teflon®), thermoplastics, certain plastics, composites, and other synthetic materials suitable for gas environments. In non-gas working environments, secondary sealing element  116  may be constructed from other materials.  
         [0029]     Closure member  112  is preferably constructed from a steel, stainless steel, ceramic, plastic, or other suitable material. Threaded insert  108 , seat retainer  118 , and spring  110  are preferably constructed from metallic materials but may also be formed from plastics, thermoplastics, and other suitable materials.  
         [0030]      FIG. 3  illustrates valve assembly  100  in an open position supporting fluid flow in a free flow direction  124 . As pressure within port  106  increases, spring  110  is compressed and closure member  112  disengages primary sealing element  114 . Flow  130  is then allowed to move between closure member  112  and primary sealing element  114 . Flow  128  continues through port  104  and out of valve body  102 . With closure member  112  disengaged from primary sealing element  114 , flow  130  will pass through gap  132  between the closure member and the primary sealing element. Solid particles being carried by flow  130  may tend to deposit within gap  132  or act to erode the sealing surfaces of closure member  112  and primary sealing element  114 .  
         [0031]      FIG. 4  illustrates valve assembly  100  in a closed position operating against flow  122  in a checked direction. As the fluid pressure is increased in port  104 , closure member  112  compresses primary sealing element  114  into groove  126  until the closure member is in sealing contact with the secondary sealing element  116 . This sealing contact is initially at a sealing diameter that increases as primary sealing element  114  is compressed. During this compression, the sealing element expands radially into groove  126  and moves upward and outward along closure member  112 . The axial movement of closure member  112  relative to primary sealing element  114  not only provides a sealing engagement but also acts as a wiper, cleaning debris from the surface of the closure member.  
         [0032]     Thus, as closure member  112  transitions from the position of initial engagement with primary sealing element  114 , as shown in  FIG. 3 , to the final position of engagement with the secondary sealing element  116 , the outer sealing surface of the closure member is wiped clean of sand and debris by primary sealing element  114 . This wiping action ensures that even in the presence of a high solids content flow, the sealing diameter between closure member  112  and sealing element  114  has a sealing engagement that is substantially free of debris.  
         [0033]     Secondary sealing element  116  provides a redundant sealing interface and limits the axial translation of closure member  112  relative to sealing element  114 . In certain applications, sealing element  116  also provides a sealing material substantially impermeable to gas. One problem with elastomeric seals is that some elastomeric materials are susceptible to explosive decompression in high pressure gas environments with rapidly changing pressures. High pressure gas can permeate into the elastomeric material and, when the pressure rapidly drops, the gas within the seal rapidly expands and can damage the seal. The construction of secondary sealing element  116  from a polymeric, or other suitable, material improves the performance of the valve in gas environments. In non-gas environments, other materials may be used.  
         [0034]     The combination of the primary  114  and secondary  116  sealing elements thus provides a redundant sealing engagement with closure member  112 . The wiping action of primary sealing element  114  also allows the utilization of considerably lower spring force, thereby lowering the free flow cracking pressure. This lower cracking pressure greatly reduces the localized fluid flow velocity through gap  132 , thereby reducing erosion on the closure member and the sealing elements.  
         [0035]     One exemplary use of a check valve assembly is in a reciprocating piston-style pump as shown in  FIG. 5 . Pump assembly  200  includes body  202  and a reciprocating piston  204  forming pumping chambers  206  and  208 . Assembly  200  also includes two dual check valve assemblies  210  and  216 . Check valve assembly  210  includes inlet check valve  212  and outlet check valve  214 . Check valve assembly  216  includes inlet check valve  218  and outlet check valve  220 . Flow line  222  provides fluid communication between check valve assembly  210  and chamber  208 . Flow line  224  provides fluid communication between check valve assembly  216  and chamber  206 . Inlet line  226  provides fluid to pump assembly  220  and outlet line  228  carries fluid from the assembly.  
         [0036]     In operation, as piston  204  moves to the right, chamber  208  increases in size and chamber  206  decreases in size. The increase in size of chamber  208  causes a pressure drop in line  222 , which connects to valve assembly  210  between inlet check valve  212  and outlet check valve  214 . This decrease in pressure closes outlet check valve  214  and opens inlet check valve  212  pulling fluid from inlet line  226 . The fluid from inlet line  226  flows through inlet check valve  212  and line  222  into chamber  208 . The decrease in size of chamber  206  causes a pressure increase in line  224 , which connects to valve assembly  216  between inlet check valve  218  and outlet check valve  220 . This increase in pressure closes inlet check valve  218  and opens outlet check valve  220  allowing fluid to flow into outlet line  228 . The fluid from line  224  flows through outlet check valve  220  and into outlet line  228 .  
         [0037]     As piston  204  moves to the left, the reverse procedure occurs and chamber  206  increases in size as chamber  208  decreases in size. The increase in size of chamber  206  causes a pressure drop in line  224 , which connects to valve assembly  216  between inlet check valve  218  and outlet check valve  220 . This decrease in pressure closes outlet check valve  220  and opens inlet check valve  218  pulling fluid from inlet line  226 . The fluid from inlet line  226  flows through inlet check valve  218  and line  224  into chamber  206 . The decrease in size of chamber  208  causes a pressure increase in line  222 , which connects to valve assembly  210  between inlet check valve  212  and outlet check valve  214 . This increase in pressure closes inlet check valve  212  and opens outlet check valve  214  allowing fluid to flow into outlet line  228 . The fluid from line  222  flows through outlet check valve  214  and into outlet line  228 .  
         [0038]     Referring now to  FIGS. 6 and 7  a schematic representation of a downhole formation testing tool  290  is shown. Tool  290  comprises a dual probe section  305 , gauge section  309 , pump section  300 , and multi-chamber sections  310 . Probe section  305  includes two sample acquisition probes  307  that engage the wall of a wellbore and provide a fluid conduit between the formation surrounding the wellbore and tool  290 . Gauge section  309  provides analytical tools for evaluating the properties, such as density, viscosity, etc, of the fluid drawn into the tool. Multi-chamber sections  310  provide storage containers for samples of fluid that are collected for return to the surface for further evaluation.  
         [0039]     Pump section  310  includes the components described in reference to  FIG. 5 . Section  310  includes pump assembly  200  including reciprocating piston  204  forming pumping chambers  206  and  208 . Inlet check valves  212  and  218  allow fluid to flow from flowline  226  into chambers  206  and  208 . Outlet check valves  208  and  220  allow fluid to flow out of chambers  206  and  208  into flowline  228 . Pump assembly  200  operates to draw fluid into probe section  305  and through flowlines  226  and  228  out to multi-chamber sections  310 .  
         [0040]     While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.