Patent Publication Number: US-2016236835-A1

Title: Thief hatch

Description:
BACKGROUND 
     Generally, storage containers such as above-ground or below-ground storage tanks include an opening to provide access to the interior of the tank. This opening may be designed to accept a venting device such as a thief hatch, which provides a re-sealable opening through which a thief or other tool may be inserted into the interior of the storage tank. 
     The internal pressure (e.g., internal vapor pressure) within a storage tank may fluctuate depending on various factors such as, for example, the amount of fluid in the tank, the volatility of the fluid in the tank, the temperature of the fluid in the tank, the ambient temperature outside the tank, a thermal conductivity of the walls of the tank, and so on. As vapor pressure in the storage tank increases, it often becomes necessary to relieve the pressure in a controlled fashion. In this regard, the thief hatch may provide a seal that blocks fluid communication between an interior of the storage tank and an exterior of the storage tank when the vapor pressure within the tank remains below a defined threshold but that enables or opens a path for fluid communication between the interior of the tank and the exterior of the tank once the vapor pressure within the tank exceeds the threshold. 
     Existing thief hatches or relief valves for storage containers exhibit a significant drawback in that the actuating mechanisms used to move a seal of the thief hatch between closed and open positions are capable of moving within multiple degrees of freedom. As a result, these actuating mechanisms tend to toggle during operation and often stick in an open position. Remaining open for long periods of time allows vapors and/or liquids (e.g., natural gas, oil, gasoline, etc.) to freely escape from the corresponding tanks. This excessive venting is unacceptable in many applications where tight sealing and controlled venting is key, such as, for example, in instances where strict environmental emissions standards are enforced. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter. 
     One embodiment provides a thief hatch configured to couple with a storage container having an opening. The thief hatch includes a base configured to affix to the storage container. The base has an annular lip that defines an opening, where the opening of the base and the opening of the storage container share a longitudinal center axis. The thief hatch also includes a cap coupled to the base, a seal disposed between the base and the cap, an actuating mechanism disposed on an interior surface of the cap, and at least one structural constraint. The actuating mechanism is configured to exert a biasing force on the seal to bias the seal against the annular lip of the base. In one embodiment, the structural constraint may be a pin configured to prevent lateral movement of the actuating mechanism such that the actuating mechanism moves exclusively along the longitudinal center axis. 
     Another embodiment provides a system for venting pressure from an interior of a storage container. The system includes a base having an annular lip that defines a central opening about a longitudinal axis. The central opening is configured to be in fluid communication with the interior of the storage container. The system also includes a cap rotatively coupled to the base and a seal assembly disposed between the base and the cap. The seal assembly includes a seal that is indirectly coupled to an actuating mechanism configured to exert a biasing force on the seal toward the annular lip, and the seal assembly is configured such that the actuating mechanism moves exclusively along the longitudinal axis between a closed position in which the seal blocks the central opening and an open position in which the seal is retracted from the central opening. 
     Yet another embodiment provides a method of manufacturing a thief hatch for coupling with a storage container, where the thief hatch includes a base with an annular lip that defines a central opening, a cap having exterior and interior surfaces, a seal disposed between the base and the cap, an actuating mechanism having first and second ends and in communication with the seal, and at least one structural constraint for limiting the movement of the actuating mechanism. The method includes the steps of (1) rotatively coupling the cap to the base; (2) enclosing the first end of the actuating mechanism within a structural insert configured to nest within a mating insert sleeve; (3) positioning the second end of the actuating mechanism within the insert sleeve such that the second end is disposed on the interior surface of the cap; (4) rotatively engaging a retention tab of the structural insert with a helical groove of the insert sleeve until the retention tab is retained within a longitudinal recess of the insert sleeve; and (5) affixing the structural constraint to the cap such that the structural constraint protrudes from the interior surface of the cap in a manner that prevents lateral movement of the actuating mechanism. The actuating mechanism may be a compression spring or any other appropriate biasing element. 
     Other embodiments are also disclosed, and additional objects, advantages and novel features of the technology will be set forth in part in the following description, and in part will become more apparent to those skilled in the art upon examination of the following, or may be learned from practice of the technology. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention, including the preferred embodiment, are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. Illustrative embodiments of the invention are illustrated in the drawings, in which: 
         FIG. 1  illustrates a schematic of one embodiment of a storage tank system having an improved thief hatch; 
         FIG. 2  illustrates a top perspective view of one embodiment of an improved thief hatch; 
         FIG. 3  illustrates a cross-sectional view of the thief hatch of  FIG. 2 ; 
         FIG. 4  illustrates a top perspective view of a pre-assembly insert sleeve of the thief hatch of  FIGS. 2-3 ; 
         FIG. 5  illustrates a top perspective view of a post-assembly insert sleeve of the thief hatch of  FIGS. 2-3 ; 
         FIG. 6  provides a flow diagram detailing an exemplary manufacturing process for the thief hatch of  FIGS. 2-3 ; 
         FIG. 7  illustrates a front perspective view of the thief hatch of  FIGS. 2-3  in a partially assembled state; 
         FIG. 8  illustrates a side perspective view of a seal assembly of the thief hatch of  FIGS. 2-3  in a partially assembled state; and 
         FIG. 9  illustrates a bottom perspective view of the seal assembly of  FIG. 8  in a partially assembled state. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are described more fully below in sufficient detail to enable those skilled in the art to practice the system and method. However, embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken in a limiting sense. 
     Embodiments of the improved thief hatch described below provide an elegant solution to the excessive venting problems discussed above. In general, the described thief hatch provides a means to simply but precisely control the venting of fluids or vapors stored within a storage container or tank so as to ensure that the valve or seal opens when a pressure within the container reaches a defined threshold, but also promptly closes once sufficient pressure has been relieved and the pressure level within the container has returned to an acceptable level. 
       FIG. 1  provides a schematic of one embodiment of a storage tank system  10  having a storage tank  12  and an improved thief hatch  100 . Storage tank system  10  may be a component of a variety of applications in a number of industries, including, but not limited to, the oil and gas, agricultural, and/or medical fields. Fluid or vapor stored within storage tank  12  may over time undergo an increase in pressure. In certain circumstances, it may become desirable to vent or release pressure from an interior  16  of storage tank  12  that is above a threshold pressure. To accomplish this release, storage tank  12  includes thief hatch  100 , which is configured to periodically open fluid communication between interior  16  of storage tank  12  and an environment  18  external to storage tank  12  when the pressure within interior  16  of storage tank  12  exceeds a threshold pressure. In this manner, fluid or vapor may be vented from storage tank  12  as indicated by arrows  20 . Once the internal pressure of storage tank  12  falls below the threshold pressure, the seal assembly of thief hatch  100  automatically closes and re-seals, thereby blocking fluid communication between the interior  16  of storage tank  12  and the external environment  18 . 
     As discussed in greater detail below, thief hatch  100  includes various features to improve operation, performance, and reliability over existing thief hatches. For example, thief hatch  100  features an actuating mechanism that is physically constrained in its mobility. In this regard, thief hatch  100  may move between the open and closed positions exclusively along a longitudinal axis denoted by an axis Y. As detailed below, this constraint prevents a seal assembly of thief hatch  100  from toggling during operation and becoming stuck in an open position, which, if left unattended, leads to the over-venting of fluid or vapor from tank  12  into the environment. 
       FIGS. 2-3  illustrate respective top perspective and sectional views of one embodiment of improved thief hatch  100 . Thief hatch  100  includes a cap  102  that is rotatively coupled to a base  104  via a biasing hinge  108  that biases cap  102  toward an open position. Cap  102  may be secured in a closed position via a releasable latch  106 , which engages with a latch pin  109 . 
     Thief hatch  100  may be mechanically installed on a storage tank (not shown) such that base  104  is disposed about an opening of the storage tank. Base  104  may be attached to the storage tank using bolts, rivets, welds, or any other suitable means and may include an annular lip  105  that defines an opening  107 . Annular lip  105  lies concentric to the opening of the storage tank, and a longitudinal axis, Y, may intersect the common center of opening  107  and the opening of the storage tank. 
     In operation, thief hatch  100  is configured to seal the opening of the storage tank when in a closed position and expose the opening of the tank when in an open position. Whether the hatch  100  resides in a closed or open position is dependent upon an internal pressure within the tank. That is, thief hatch  100  remains closed unless and until the internal pressure within the tank reaches a threshold pressure, at which point thief hatch  100  opens to allow fluid communication between the interior of the tank and the ambient environment, thereby releasing pressure from the tank. Once the internal pressure within the tank returns to a point below the threshold level, thief hatch  100  returns to the closed position. 
     To accomplish this type of reliable venting, thief hatch  100  features a seal assembly  110  that includes a structural insert  112 , an insert sleeve  114 , and an actuating mechanism such as a compression spring  116 . In this embodiment, the actuating mechanism is formed of a compression spring biased to its extended position. In other embodiments, the actuating mechanism may be a biasing element of any appropriate size, shape, type, material, and/or configuration. 
     Structural insert  112  may be configured to slidably nest within insert sleeve  114  in a way that fully envelops compression spring  116 . In addition, structural insert  112  may include an annular pressure seal  115  that is adapted to form a sealed connection against annular lip  105  of base  104  when biased against annular lip  105 . Together, structural insert  112  and insert sleeve  114  interact to manipulate compression spring  116  in a manner that causes the compression and decompression of spring  116 . This compression and decompression translates to longitudinal movement of seal  115  along axis Y. 
     In further detail, a first end  118  of spring  116  may be disposed within structural insert  112 , while a second end  120  of spring  116  may be disposed within insert sleeve  114  such that first end  120  abuts an interior surface  122  of cap  102 . To accommodate the nesting of structural insert  112  within insert sleeve  114 , sleeve  114  may include a set of helical grooves  124  and corresponding longitudinal recesses  126 , shown in  FIG. 4 . Helical grooves  124  may serve as an assembly guide for retention tabs  128  ( FIG. 3 ) of structural insert  112 . In this regard, structural insert  112  may be positioned such that retention tabs  128  ( FIG. 3 ) engage with helical grooves  124  and rotate clockwise until they disengage with helical grooves  124  and engage with longitudinal recesses  126  in an assembled position. 
       FIGS. 2-3 and 5  illustrate exemplary structural constraints that may be secured to cap  102  to constrain the movement of seal assembly  110  in a longitudinal direction along axis Y. In this embodiment, the structural constraints take the form of pins  130 , which may protrude from interior surface  122  of cap  102  at each vertex  132  ( FIG. 5 ) of helical grooves  124  and longitudinal recesses  126 . Pins  130  secure retention tabs  128  within longitudinal recesses  126 , thereby preventing any lateral movement of retention tabs  128  and structural insert  112  and, as a result, restricting the movement of compression spring  116  to a longitudinal direction along axis Y. 
     When spring  116  is compressed by rising pressure within the interior of the storage tank, retention tabs  128  slide upward within recesses  126  in a longitudinal direction denoted by arrow A in  FIG. 3 . This longitudinal movement causes seal  115  to retract from annular lip  105 . This motion retracts seal  115  from annular lip  105  and opens fluid communication between the interior of the tank and the ambient environment. When the pressure on the interior of the tank decreases, spring  116  relaxes and retention tabs  128  slide downward in a longitudinal direction denoted by arrow B in  FIG. 3 . Seal  115  is, in turn, biased toward annular lip  105  to reestablish a sealed connection between the interior of the tank and the ambient environment. Because pins  130  prevent lateral movement of structural insert  112  and compression spring  116 , there is no risk that structural insert  112  will partially slide free horizontal recesses  126  and into helical grooves  124  during operation. Thus, the opening and closing of seal assembly  110  remains consistently and predictably smooth. 
     In one embodiment, pins  130  may be formed of metal and threadably secured to cap  102 . It should be understood that pins  130  may be any type of structural constraint of any appropriate size, shape, type, material, and/or configuration. In addition, pins  130  may be threadably connected, press fit, adhered, or attached to cap  102  in any appropriate and effective fashion. 
     Structural constraints such as pins  130  enable thief hatch  100  to precisely relieve pressure from the tank each and every time relief becomes necessary. Because the movement of structural insert  112  and compression spring  116  is restricted to a longitudinal direction along axis Y, these components cannot toggle or shift during operation. As a result, there isn&#39;t an opportunity for retention tabs  128  of structural insert  112  to slip out of longitudinal recesses  126  and into helical grooves  124  during operation. Thus, seal assembly  110  cannot stick in an open position even after sufficient pressure has been vented from the interior of the storage tank, and thief hatch  100  is able to operate consistently within a single, longitudinal degree of freedom to open fluid communication between the interior of the tank and the ambient environment only as necessary as dictated by the tank pressure level. 
       FIG. 6  provides a flow chart detailing an exemplary process  150  for manufacturing thief hatch  100 . Process  150  initiates when cap  102  is rotatively coupled to base  104  ( 152 ) via biasing hinge  108 . Biasing hinge  108  may incorporate or leverage a biasing element such as a torsion spring or other actuating mechanism configured to bias cap  102  toward an open position. Latch  106  may be used to counteract the force of biasing hinge  108  to retain cap  102  in a closed position as desired. 
     Once cap  102  has been attached to base  104 , seal assembly  110  may be assembled. Thus, process  150  may continue with the positioning of first end  118  of compression spring  116  within structural insert  112  ( 154 ), as shown in  FIG. 7 . Next, and as shown in  FIG. 8 , second end  120  of compression spring  116  may be positioned within insert sleeve  114  ( 156 ) such that second end  120  is disposed upon interior surface  122  of cap  102 . The steps of coupling cap  102  to base  104  ( 152 ) and positioning compression spring  116  within structural insert  112  and insert sleeve  114  ( 154  and  156 ) may occur in any desired or appropriate order. 
     Exemplary method  150  continues with the attachment of structural insert  112  to insert sleeve  114  in a manner that fully encompasses compression spring  116  within a shell formed of structural insert  112  and insert sleeve  114 . To accomplish this, retention tabs  128  may be engaged with helical grooves  124  ( FIG. 3 ) ( 158 ) and rotated in a generally clockwise direction until retention tabs  128  engage with longitudinal recesses  126  ( 160 ), resulting in a slidable coupling between structural insert  112  and insert sleeve  114  in which retention tabs  128  of structural insert  112  slide along longitudinal recesses  126 .  FIG. 9  illustrates a top perspective view of seal assembly  110  after structural insert  112  has been nested within insert sleeve  114 . 
     After structure insert  112  has been coupled to insert sleeve  114 , at least one structural constraint such as pin  130  may be affixed to cap  102  ( 162 ) such that pin  130  protrudes from interior surface  122  of cap  102  in a manner that prevents lateral movement of structural insert  112  and, in turn, compression spring  116 . In one embodiment, pin  130  may be placed such that its edge aligns with a vertex  132  of helical groove  124  and longitudinal recess  126 . As discussed above, pin  130  may be affixed to cap  104  in any appropriate manner, including a threaded connection, an adhered connection, a press fit, and so on. 
     Method  150  results in a seal assembly  110  that moves within one degree of freedom between the closed and open positions along longitudinal axis Y, thereby preventing any toggling of structural insert  112  and compression spring  116  during operation and preventing seal assembly  112  from becoming stuck in an open or partially open position. As a result, thief hatch  100  provides a safer, more precisely controlled, and more environmental friendly alternative to existing thief hatches or relief valves, which commonly stick in an open position and freely vent into the ambient environment. 
     Although the above embodiments have been described in language that is specific to certain structures, elements, compositions, and methodological steps, it is to be understood that the technology defined in the appended claims is not necessarily limited to the specific structures, elements, compositions and/or steps described. Rather, the specific aspects and steps are described as forms of implementing the claimed technology. Since many embodiments of the technology can be practiced without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.