Patent Publication Number: US-6666230-B1

Title: Pressure relief system with trigger activated valve

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to pressurized fluid systems and more particularly, but not by way of limitation, to a pressure relief system which uses a trigger assembly with a collapsible member to establish a bypass or shutdown path for a pressurized fluid in response to an overpressure condition. 
     BACKGROUND 
     Pressurized fluid systems are typically provided with pressure relief capabilities to prevent the possibility of injury to humans and damage to equipment in the event of an overpressure condition. Such pressure relief systems often use a pressure responsive member that mechanically fails when subjected to a large increase in fluid pressure above a desired setpoint. 
     A particularly advantageous pressure relief system uses a buckling pin arrangement such as taught by U.S. Pat. No. 4,724,857 issued to Taylor. In such a system, the pin is placed under compressive load along an axial length of the pin by the pressure of the fluid. A sufficient increase in fluid pressure above a nominal operational level causes the pin to buckle, or collapse, allowing a plunger or other mechanism to move to a position where an overpressure path can be established to direct the fluid to reduce the pressure to a safe operational level. Such overpressure path can be established, for example, by opening a bypass valve or closing a shutoff valve. 
     While operable, it is desirable to isolate the operation of the buckling pin or other pressure responsive member from system forces associated with establishing the overpressure path for the fluid. For example, friction forces and fluid pressure can tend to offset the compressive load upon a buckling pin if the pin actuation and the valve are directly coupled. This can result in undesirably raising the set point at which the pressure responsive member begins to fail. 
     There is therefore a continued need for improvements in the art to increase the accuracy and repeatability of pressure relief systems, and it is to such improvements that the present invention is directed. 
     SUMMARY OF THE INVENTION 
     A pressure relief system is provided to detect and abate an overpressure condition in a pressurized fluid. In accordance with preferred embodiments, the system includes a housing having a housing interior surface which defines a housing interior chamber. The housing interior chamber extends along a selected axis. 
     An actuator assembly is coupled to the housing and is configured to establish an overpressure path for the pressurized fluid when a pressure of the pressurized fluid reaches a predetermined level. The actuator assembly comprises an extension sleeve which extends into and along the housing interior chamber, the extension sleeve having an extension sleeve outer surface in close proximity to the housing interior surface. The extension sleeve further has an extension sleeve interior surface which defines an extension sleeve interior chamber, said extension sleeve interior chamber extending along the selected axis. 
     A pressure response assembly is also coupled to the housing and comprises a pressure responsive member (such as a buckling pin) configured to mechanically fail in response to application of a compressive force established when the pressurized fluid reaches the predetermined level. The pressure response assembly further comprises a trigger member coupled to the pressure responsive member, the trigger member extending into and along the extension sleeve interior chamber. The trigger member comprises a first stem portion having a first stem outer surface in close proximity to the extension sleeve interior surface. 
     A number of retention members (preferably ball bearings) are provided adjacent the first stem portion of the trigger member. Each retention member extends through an aperture in the extension sleeve and into a recessed cavity formed in the housing interior surface. 
     The retention members prevent axial movement of the extension sleeve along the selected axis while the first stem portion remains adjacent the retention member. Upon mechanical failure of the pressure responsive member, the first stem portion is advanced along the selected axis past the retention member to allow the extension sleeve to advance the retention member out of the recessed cavity and along the housing interior chamber as the extension sleeve moves along the selected axis. The overpressure path for the pressurized fluid is established by the actuator assembly as the extension sleeve moves along the selected axis. 
     In this way, the trigger member, the extension sleeve and the retention members cooperate to function similarly to a “quick-disconnect” coupler, and system forces associated with the actuator assembly do not undesirably affect the set point at which the pressure responsive member begins to mechanically fail. 
    
    
     These and various other features and advantages which characterize the claimed invention will become apparent upon reading the following detailed description and upon reviewing the associated drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional view of a pressure relief system constructed and operated in accordance with preferred embodiments of the present invention and having a normally closed (NC) pressure relief valve. FIG. 1 shows the system operating in a steady state condition. 
     FIG. 2 shows the system of FIG. 1 in an overpressure condition with the pressure relief valve in an open position to establish an overpressure path for the pressurized fluid. 
     FIG. 3 is a cross-sectional view of portions of a pressure response assembly and an actuator assembly of the system of FIG. 1 in the steady state condition. 
     FIG. 4 shows the pressure response assembly and the actuator assembly of FIG. 3 in a transitional state between the steady state condition and the overpressure condition. 
     FIG. 5 shows the pressure response assembly and the actuator assembly of FIG. 3 in the overpressure condition. 
     FIG. 6 is a cross-sectional view of the actuator assembly generally taken along line  6 — 6  in FIG.  1 . 
     FIG. 7 is a cross-sectional view of the actuator assembly generally taken along line  7 — 7  in FIG.  2 . 
     FIG. 8 is a cross-sectional view of an alternative actuator assembly which can used in substitution for the actuator assembly of FIG. 1, with the actuator assembly of FIG. 8 shown in a steady state condition. 
     FIG. 9 is a cross-sectional view of the actuator assembly of FIG. 8 in an overpressure condition configuration. 
     FIG. 10 is a cross-sectional view of another alternative actuator assembly in a steady state condition. 
     FIG. 11 is a cross-sectional view of the actuator assembly of FIG. 10 in an overpressure condition. 
     FIG. 12 is a cross-sectional view of yet another alternative actuator assembly in a steady state condition. 
     FIG. 13 is a cross-sectional view of the actuator assembly of FIG. 12 in an overpressure condition. 
     FIG. 14 is a graphical illustration of a force versus deflection curve to generally illustrate force required to deflect and ultimately collapse a buckling pin of the system of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 2 show a pressure relief system  100  constructed in accordance with preferred embodiments of the present invention. The pressure relief system  100  (“system”) is preferably used as part of a larger pressurized fluid system in which a pressurized fluid is transported. The pressure relief system  100  is used to detect and abate an overpressure of the pressurized fluid and to provide an overpressure path for the fluid to reduce the possibility of injury to humans and damage to equipment. 
     The system  100  is shown to generally include a pressure response assembly  102 , a rotary actuator assembly  104  and a valve assembly  106 . The valve assembly  106  includes a normally closed (NC) ball valve  108  with a central flow-through aperture  110 . The ball valve  108  is opened by the system  100  to provide a bypass path for the fluid (as shown in FIG. 2) in the event of an overpressure condition. It will be understood, however, that the ball valve  108  can alternatively be configured to be normally open (NO) so that the system  100  closes the valve to inhibit further flow of the pressurized fluid in response to an overpressure condition. Other valve configurations are also readily contemplated, including but not limited to the use of butterfly and plug-type valves. 
     The pressure response assembly  102  includes a body portion  112  which extends from the actuator assembly  104 . A bonnet  114  is affixed to the body  112  opposite the actuator assembly  104 . The body  112  and bonnet  114  cooperate to form a chamber having respective interior portions  116 ,  116 A defined by opposing sides of a piston  120  of a trigger assembly  118 . Pressurized fluid is introduced into the portion  116  (and into the actuator assembly  104 ) via conduit  117 , as discussed below. The interior portion  116 A includes vent passageways (such as  119 ) in communication with the surrounding atmosphere. 
     The trigger assembly  118  includes a pin support  121  which axially extends from the piston  120  and projects through a central aperture in the bonnet  114 . A distal end of the pin support  121  captures and supports a collapsible member  122  which preferably comprises a buckling pin configured to fail (buckle) in accordance with Euler&#39;s Law. A distal end of the buckling pin  122  is captured and supported by a standoff assembly  124 . A removable, threaded cap  126  allows an operator to remove a failed pin  122  (as shown in FIG. 2) and install a new, straight pin (as shown in FIG.  1 ). 
     The trigger assembly  118  further includes a generally pin-shaped member  128  which axially extends from the piston  120  in a direction opposite that of the pin support  121 . Tile member  128  extends into a cylindrically shaped extension sleeve  130  which projects from a first slidable piston  132  of the actuator assembly  104 , further details of which will be discussed below. 
     The preferred construction and operation of the member  128  and the extension sleeve  130  can be seen with a review of FIGS. 3-5. For reference, these figures further show portions of the piston  120 , the pin support  121  and the actuator assembly piston  132  previously introduced in FIGS. 1 and 2. FIG. 3 corresponds to the orientation of the system  100  in FIG. 1 (i.e., a steady state condition), FIG. 5 corresponds to the orientation of the system  100  in FIG. 2 (i.e., an overpressure condition), and FIG. 4 represents a transitional state between those of FIGS. 3 and 5. 
     The member  128  comprises a first stem portion  134  with a diameter substantially that of the interior diameter of the extension sleeve  130 . The first stem portion  134  concludes with a chamfered shoulder  136  from which a second stem portion  138  extends. The second stem portion  138  has a diameter that is smaller than the diameter of the first stem portion  134 . A facing surface  140  at the distal end of the second stem portion  138  comes into a close, noncontacting relationship with an interior base surface  142  of the extension sleeve  130 . A seal  144  (preferably comprising a rubber o-ring) seals the interface between an interior surface  145  of the body portion  112  and the exterior surface of the extension sleeve  130 . 
     The body portion  112  includes a plurality of recessed cavities  146  that extend into the body portion  112  from the interior surface  145 . The cavities  146  align with apertures  148  in the extension sleeve  130  to accommodate a respective number of locking members (ball bearings)  150 , as shown in FIG. 3 . While two opposing ball bearings  150  are shown in each of FIGS. 1-5, it will be understood that any number of ball bearings  150  (four, six, eight, etc.) can be angularly arrayed about the first stem portion  134  as desired. 
     The respective geometries of the ball bearings  150 , the first stem portion  134 , the extension sleeve  130  and the cavities  146  are selected to cause the ball bearings  150  to restrict axial movement of the extension sleeve  130  in a direction toward the plunger  120  when the first stem portion  134  is adjacent the ball bearings  150  (i.e., the steady state condition of FIG.  3 ). That is, because the width of the gap between the first stem portion  134  and the interior surface  145  of the housing  112  is smaller than the diameters of the ball bearings  150 , the bearings  150  are retained within the recessed cavities  146  by the first stem portion  134  and prevent further advancement of the extension sleeve  130 . In this way, the ball bearings  150  lock the actuator assembly  104  in place in the steady state condition. 
     At the same time, there is substantially no compressive force applied to the first stem portion  134  by the ball bearings  150 , which allows the first stem portion  134  to freely slide past the bearings  150  once the fluid pressure exerted upon the piston  120  (via conduit  117 ) reaches the desired set point and initiates collapse of the buckling pin  122  (FIGS.  1  and  2 ). As the shoulder  136  passes the ball bearings  150  (FIG.  4 ), the clearance provided by the second stem portion  138  is sufficient to allow the ball bearings  150  to be advanced out of the recessed cavities  146  by the extension sleeve  130 . The actuator assembly  104  becomes “unlocked” at this point and the extension sleeve  130  advances the bearings  150  along the interior surface  145  of the body portion  112  until further movement of the extension sleeve  130  is impeded, such as by contact of the first actuator piston  132  with the body portion  112  (as shown in FIGS. 2  and  5 ). 
     The member  128 , the extension sleeve  130  and the bearings  150  thus generally cooperate in a manner similar to a “quick disconnect” coupling. Forces associated with the actuator assembly  104  and the valve assembly  106  do not undesirably raise the set point of the buckling pin  122  because of the fact that the bearings  150  lock axial movement of the extension sleeve  130  and at the same time permit substantially free axial movement of the member  128 , and because the extension sleeve  130  and the trigger member  128  are not otherwise directly coupled (note, for example, the gap between the surfaces  140  and  142  in FIG.  3 ). For completeness, it will be observed that directly coupling the trigger member  128  and the extension sleeve  130  (such as, for example, by having the surface  140  contact the surface  142 ) would allow translation of compressive forces from the actuator assembly  104  to the buckling pin  122 , thereby offsetting the compressive forces applied to the pin  122  by the pressurized fluid acting upon piston  120  and undesirably raising the set point at which mechanical collapse occurs. 
     FIG. 6 shows a cross-sectional view of the actuator assembly  104  as generally taken along line  6 — 6  in FIG. 1 (the pressure response assembly  102  of FIG. 1 has been omitted for purposes of clarity). An actuator body portion  152  cooperates with a flange  154  and the pressure response assembly body portion  112  to provide a sealed actuator assembly housing. Pressurized fluid from the conduit  117  (FIG. 1) enters the actuator assembly housing between the first actuator piston  132  and a second actuator piston  156 . The pistons  132 ,  156  are configured for sliding movement toward opposing ends of the actuator assembly housing from a retracted position to an extended position. 
     An actuator shaft  158  is transversely mounted by the body portion  152  and supports a pinion  160  (elongated rotary gear) which engages racks  162 ,  164  (teeth) in the respective pistons  132 ,  156 . The actuator shaft  140  is directly coupled to a valve shaft  166  (FIG.  1 ), which is in turn directly coupled to the ball valve  108 . In this way, rotation of the actuator shaft  158  results in rotation of the ball valve  108  to the final desired position. FIG. 7 shows the actuator assembly  104  in the fully extended position. For reference, FIG. 7 generally corresponds to the cross-sectional view taken along line  7 — 7  in FIG.  2 . 
     FIGS. 8 and 9 provide an alternative actuator assembly  204  that can be used in lieu of the actuator assembly  104  discussed above. FIG. 8 shows the actuator assembly  204  in a retracted position corresponding to the steady state condition of FIG. 1; FIG. 9 shows the actuator assembly  204  in an extended position corresponding to the overpressure condition of FIG.  2 . 
     The actuator assembly  204  includes a body portion  206  that cooperates with a flange  208  and the pressure response assembly body portion  112  to form a sealed housing. A single plunger-type piston  210  is arranged for sliding movement within the body portion  206  and supports the aforedescribed extension sleeve  130 . 
     An interior chamber  212  accommodates a transversally mounted shaft  214  upon which a pinion  216  is mounted. A rack  218  of the piston  210  engages the pinion  216  as shown. Pressurized fluid is introduced into the actuator housing via port  220  to exert pressure on the piston  210 . 
     The actuator assembly  204  is particularly useful in environments where dirty fluids (i.e. corrosive or otherwise contaminating fluids) are used, since the pressurized fluid does not come into contact with the rack  218  and pinion  216  and thus does not interfere with the operation or reliability of the system  100  over time. 
     FIGS. 10 and 11 show yet another actuator assembly  224  which can be used in lieu of the alternative configurations discussed above. The actuator assembly  224  is shown in conjunction with the aforedescribed pressure response assembly  102  and is configured to open the valve assembly  108  in generally the same manner as discussed above for the actuator assemblies  104 ,  204 . FIG. 10 shows the actuator assembly  224  in the retracted position, and FIG. 11 shows the actuator assembly  224  in the extended position. As with the actuator assembly  204 , the actuator assembly  224  is also useful in an environment where dirty fluids are used. 
     The actuator assembly  224  includes an elongated body portion  226  housing a piston  228 . The piston  228  includes a rack  230  which engages a pinion  232  mounted to a shaft  234 . The piston  218  further has a plunger  236  at one end which is slidable within a chamber  238  of the body portion  226 . Pressurized fluid is introduced into the chamber via port  240  and atmospheric air within the chamber  228  is vented through port  242 . The piston  228  is provided with a extension sleeve  243  which is generally similar to the extension sleeve  130  and which cooperates with the trigger member  128  of the pressure response assembly  102  as discussed above. 
     FIGS. 12 and 13 provide yet another alternative actuator assembly  244  which employs a Scotch yoke arrangement in lieu of a rack and pinion arrangement. The actuator assembly  244  includes an elongated body portion  246  housing a piston  248 . The piston  248  supports a cylindrical roller  250  which is engaged by a yoke  252  as shown. The yoke  252  is mounted to a shaft  254  which in turn is coupled to the valve shaft  116  (FIG.  1 ). Movement of the actuator assembly  244  to the extended position (FIG. 13) induces a camming action which rotates the ball valve  108  to the desired position. 
     A plunger  256  is slidable within a chamber  258  of the body portion  246 . Pressurized fluid is introduced into the chamber  258  via port  260  and atmospheric air within the chamber  258  is vented through port  262 . The piston  248  further includes a extension sleeve  264  opposite the piston  248  which cooperates with the member  128  of the pressure response assembly  102  as discussed above. 
     Having now concluded a discussion of various alternative constructions of the system  100 , operational considerations will now be briefly addressed. As will be recognized by those skilled in the art, buckling pins such as  122  generally provide well controlled response characteristics to axially directed compressive forces. The axial force sufficient to cause the buckling pin  122  to buckle is the “buckling limit.” The buckling limit depends on the modulus of elasticity of the material of the buckling pin and the particular geometry for the buckling pin. 
     FIG. 14 provides a generalized graphical representation of a buckling pin deflection curve  300  plotted against a deflection distance x-axis  302  and a compressive force magnitude y-axis  304 . Compressive forces below a critical force Fc will tend to allow the buckling pin  122  to remain within its elastic limit. Thus, increases in compressive force up to the critical force Fc will impart a slight bowing to the pin  122 , but a relaxation of the compressive force will allow the pin  122  to return to the original straight configuration. 
     However, once the critical force Fc is reached (i.e., axial deflection reaches a distance X 1 ), the pin  122  will begin to buckle (mechanically fail). The amount of force thereafter required to continue buckling of the pin is not constant, but drops off rapidly as shown by curve  300 . 
     It will now be seen that an advantage of the present invention (as embodied herein) is the isolation of system forces relating to the activation of the valve assembly  106  from the compressive forces acting upon the buckling pin  122 . Another advantage is that the actuator assembly is preferably precharged with the pressurized fluid, so that activation of the valve can take place quickly once the retaining support of the buckling pin  122  is removed. 
     Although various embodiments have been presented herein, it will be understood that numerous changes and modifications arc readily contemplated and not listed herein for brevity. For example, it will be understood that any number of different mechanical linkages can be used within the actuator assembly to activate the valve. Moreover, although a rotary activation has been described, such is not necessarily limiting to the scope of the appended claims. Other pressure responsive members such as a shear pin or a frangible disk can readily be used in place of the buckling pin disclosed herein. The use of ball bearings (such as  150 ) as retention members to facilitate the relative movement of the member  128  and extension sleeve  130  is preferred, but other configurations of retention members (Such as rollers or bushings) can also be employed. 
     For purposes of the appended claims, mechanical failure will be understood as describing, for example, the buckling of a buckling pin such as  122 , the shearing of a shear pin, or the bursting of a disc membrane. Overpressure path will be understood to describe a redirection of the flow of the pressurized fluid, such as by a bypass path (as shown in FIG. 2) or a shutdown (interruption) in the original flow. Other piston-shaft coupling arrangements besides a rack and pinion arrangement to generate a torque are readily contemplated and are well within the ability of those skilled in the art to implement, such as configurations using belts, springs, chain drives, or linkages. 
     It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.