Patent Document

RELATED APPLICATIONS 
     This application makes a claim of domestic priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/178,523 filed May 15, 2009. 
    
    
     BACKGROUND 
     Pressurized fluid systems are provided with pressure relief capabilities to prevent injury to personnel and damage to equipment. In the event of an overpressure condition, a pressure relief valve redirects the fluid flow to a bypass path or to a shut-off path. Pressure relief valves are usually configured to be either normally open or normally closed to fluid passage. Exemplary pressure relief valve assemblies are taught by U.S. Pat. No. 7,438,087 issued to Taylor. 
     Some types of pressure relief valves use a spring loaded valve member that is urged against a valve seat and configured to permit the pressurized fluid to contactingly engage the normally closed valve member. The spring maintains the valve member in the closed position, while the fluid pressure opposes the spring force to urge the valve member to the open position. 
     If the valve is operated at a working fluid pressure that is relatively close to the pressure setpoint, which is the pressure at which the valve will open to establish a bypass path, the net force applied to the valve member by the spring may be insufficient to maintain a bubble-tight seal. The valve will thus simmer, permitting small amounts of pressurized fluid to escape through the assembly. Depending on the nature of the pressurized fluid, this can result in a number of undesired effects including environmental contamination (pollution), loss of product volume and hazards to personnel and/or downstream equipment. 
     One way in which prior art solutions have endeavored to reduce the effects of simmering is to remove the valve member from the inlet fluid pressure through the use of an upstream rupture disk. The rupture disk generally serves as a membrane to isolate the downstream valve from normal fluid pressure. The rupture disk is intended to retain the fluid until the overpressure condition is reached, upon which the disk ruptures and the pressurized fluid passes to the pressure relief valve member. In such case, the fluid pressure is sufficient to overcome the spring bias force on the valve member, moving the valve member to the open position for fluid passage to a bypass path. 
     A limitation with this approach includes the fact that any fluid pressure that may develop between the upstream and downstream devices, such as via a leak through or around the rupture disk, will generally tend to alter the differential pressure across the upstream device. In such case, the set point at which the upstream device opens will be undesirably higher than the specified level. 
     It is thus common to use pressure indicators to detect such buildup of pressure between the upstream and downstream devices. When an undesirably high level of intermediate pressure is detected, maintenance action is required to address the situation, which can include replacing the upstream rupture disk, involving substantial effort and downtime to access and replace the failed rupture disk. 
     Another limitation associated with the use of rupture disks is the fact that while rupture disks are generally intended to open in a controlled manner and remain in a single piece, the disks can separate upon rupturing and fragments can be carried by the fluid flow to the main pressure relief valve. This is undesirable as such fragments can interfere with the proper opening and subsequent closing of the main valve. 
     There continues to be a need for improvements in the manner in which overpressure conditions in pressurized fluid system configurations can be detected and relieved. It is to these and other improvements that various embodiments of the present invention are generally directed. 
     SUMMARY 
     Various embodiments of the present invention are generally directed to a valve assembly that is configured to relieve an overpressure condition of a pressurized fluid when the fluid reaches a setpoint pressure, and to reduce the occurrence of simmering when the fluid is near the setpoint pressure. 
     In accordance with some embodiments, the valve assembly comprises a housing with an inlet and an outlet to form a conduit for a pressurized fluid. A normally closed valve member is axially displaceable within the housing to engage a valve seat to prevent a flow of the pressurized fluid along the conduit. 
     A biasing member applies a bias force to the valve member to retain the valve member against the valve seat. A piston within the valve member contactingly engages the pressurized fluid. A mechanically collapsible member resists axial movement of the piston responsive to said contacting engagement of the pressurized fluid. 
     The piston and collapsible member decouple the bias force supplied by the biasing spring member upon the valve member from a force upon the valve member applied by the pressurized fluid. In this way, a bubble-tight seal is maintained even if the working pressure of the fluid is just below the setpoint pressure at which the valve assembly opens. 
     Various other features and advantages of presently preferred embodiments present invention will be apparent from the following description when read in conjunction with the accompanying drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary pressure relief valve assembly in a closed position to inhibit passage of a pressurized fluid. 
         FIG. 2  shows the valve assembly of  FIG. 1  in an open position to establish a bypass path for the pressurized fluid. 
         FIG. 3  shows an elevational representation of a piston of the valve assembly of  FIG. 1 . 
         FIG. 3A  shows a bottom plan, partial cross-sectional representation of the piston as viewed along line  3 A- 3 A in  FIG. 3 . 
         FIG. 4  is an elevational, cross-sectional representation of a valve member of the valve assembly. 
         FIG. 5  shows a relative orientation of the piston and valve member when the valve assembly is in the closed position. 
         FIG. 6  shows a relative orientation of the piston and valve member when the valve member is in the open position. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention are generally directed to an apparatus for detecting and abating an overpressure condition in a pressurized fluid. A normally closed valve assembly establishes a bubble-tight seal to impede a flow of pressurized fluid. The valve assembly opens when a predetermined setpoint pressure is reached. The occurrence of simmering of pressurized fluid through the closed seal interface is minimized, even if the operational pressure of the fluid is just below the setpoint pressure. 
       FIG. 1  shows an exemplary pressure relief valve assembly  100 . It is contemplated that the pressure relief valve assembly  100  is incorporated into a larger pressurized fluid transport system (not shown), such as a pipeline system. 
     The pressurized fluid can take any number of forms such as but not limited to volatile hydrocarbons, steam, fuel oil, fresh or salt water, etc. Any number of working and setpoint pressures can be utilized depending on the requirements of a given application. The valve assembly  100  is maintained in a normally closed (NC) position during normal operation as depicted in  FIG. 1 . Once the pressure of the fluid reaches the predetermined setpoint pressure, the valve assembly  100  transitions to an open position as shown in  FIG. 2  to provide a bypass path for the pressurized fluid. 
     A valve body  102  includes an inlet  104  and an outlet  106  to form an interior conduit  108 . A valve member  110  is configured for reciprocal movement along a central axis through the body  102 . The valve member  110  includes a main valve piston  111  with an annular valve engagement surface  112 . The surface  112  engages an annular sealing member  114  to form a seal interface. 
     The sealing member  114 , also referred to as a valve seat, can take any number of forms including metal, vulcanized rubber (with or without a reinforcing metal insert), nylon, or some other suitable material. The sealing member  114  is supported by a cylindrical insert  116  and an outer sleeve member  118 . 
     A biasing member  120 , characterized in  FIG. 1  as a coiled spring, engages the valve member  110  to urge the annular valve engagement surface  112  against the sealing member  114  in a normally closed manner. The spring  120  is compressed between an upper surface  122  of the valve member  110  and a lower base surface  124  of a threaded first insert  126 . 
     The first insert  126  engages a threaded second insert  128 . The threaded second insert  128  engages a cover plate  130  which is secured to the valve body  102  via fasteners  132 . A user can rotate the first insert  126  to axially advance or retract the lower base surface  124  toward or away from the valve member  110 , thereby adjusting the net spring force magnitude imparted to the valve member  110 . It is contemplated that this operation will take place during manufacturing testing and certification of the valve assembly, but subsequent field adjustments of the assembly can be carried out in this manner as well. 
     An interior carriage support  134  extends inwardly as shown to maintain the reciprocal movement of the valve member  110  along the desired axial path. A low friction sealing member  136 , such as an annular o-ring, accommodates such axial movement while retaining the pressurized fluid within the conduit  108 . 
     A reciprocating piston  140  engages the valve member  110 . The piston  140  includes a piston head  142  housed within a piston head chamber  144  of the valve member  110 , and an upwardly depending piston stem  146  that extends through a tube extension  147  of the valve member  110 . 
     A distal end of the piston stem  146  is coupled with a first end of a collapsible member  148 , characterized as a buckling pin. An opposing second end of the collapsible member  148  is secured by a threaded cap nut  150 , which is supported by a top plate  152 . The top plate  152  is supported above the cover plate  130  via threaded standoffs  154  and threaded nuts  156 . 
     The piston  140  and the pin  148  decouple the fluidic force of the pressurized fluid from the spring force supplied by the spring  120 , allowing the entire force of the spring to be maintained upon the valve member  110  at all times. This advantageously reduces, or wholly eliminates, any simmering of the pressurized fluid through the seal interface while the valve member  110  remains in the closed position, even when the working pressure is very close to setpoint (e.g., within 2% or less). 
     In at least some embodiments, the diameter of the cross-sectional opening of the seal  114 , denoted as distance X in  FIG. 2 , is nominally set to be equal to the outer diameter of a medial portion of the valve member  110  (shown as distance Y in  FIG. 2 , so that X=Y). The effective diameter of the piston head  142 , shown as distance Z in  FIG. 2 , is set to be greater than the diameter X of the seal  114  (i.e., Z&gt;X). 
     Because of the balanced X=Y condition, upon collapse of the pin  148  ( FIG. 2 ) any downstream fluidic pressure at the outlet  106  will tend to have no effect on the effective spring force on the valve member  110 . That is, to the extent that there is any fluid pressure at outlet  106 , this pressure will exert both upwardly and downwardly directed forces upon the valve member  110 , and these fluidic forces will be nominally equal and will cancel one another. The valve assembly will thus open as the larger upwardly directed fluidic pressure force F P  upon the piston overcomes the smaller downwardly directed spring force F B  upon the valve member (F P &gt;F B ). 
     Because of the unbalanced Z&gt;X condition, while the valve member remains in the closed position ( FIG. 1 ) there will be a net force F V  from the pressurized fluid that aids the spring force F B  in holding the valve member  110  against the seal  114 . This net force F V  will be proportional to the difference between the larger diameter of the piston head  142  and the smaller diameter of the seal  114  (i.e., F V  α Z−X). This net force will be applied downwardly upon the valve member  110  just below the piston head  142  in the gap between the piston head and the valve member (see  FIG. 1 ). 
     Once the pin  148  buckles, the piston  140  will be driven upwardly against the valve member  110  and will effectively become a “part” of the valve member  110 . At this point the spring  120  will be the only member operating to maintain the valve member  110  on the seal  114 , as the net fluidic forces upon the valve member  110  will be balanced as discussed above. 
       FIG. 3  is an elevational representation of the piston  140 .  FIG. 3A  shows an end view of the piston along line  3 A- 3 A in  FIG. 3 . The piston head  142  includes opposing upper and lower surfaces  157 ,  158 . The lower surface  158  is configured to receive contacting engagement of a portion of the pressurized fluid. The fluid force F P  upon the piston  140 , denoted in  FIG. 3  by vector arrow  160 , will be provided in relation to the pressure of the fluid and the areal extent of the piston lower surface  158 . 
     This force will be opposed by the collapsible member  148  (see  FIG. 1 ), which will resist movement of the piston  140  via a compression force F C  until the member mechanically collapses in accordance with Euler&#39;s Law of Axial Loading (see  FIG. 2 ). As used herein, mechanical collapse will be understood as a permanent deformation of the collapsible member so that the member is altered to take a different shape. 
     An annular sealing member  162  is disposed within an annular recess of the piston head  142 , as shown in  FIG. 3 . The piston stem  146  includes a notched surface  163  to provide a generally D-shaped cross-sectional shape for the stem, as shown in  FIG. 3A . This provides a vent path for entrapped air as the piston  140  is driven upwardly. 
       FIG. 4  shows the valve member  110  in greater detail. The aforementioned piston chamber  144  includes an annular sidewall  164  and opposing upper and lower circumferentially extending surfaces  166 ,  168 . 
     The annular sealing member  162  of the piston head  142  (see  FIG. 3 ) establishes a fluidic seal against the annular sidewall  164 . The upper surface  157  of the piston head  142  ( FIG. 3 ) contactingly abuts the upper surface  166  when the pin  148  collapses and the piston  140  is driven upwardly, as in  FIG. 2 . A portion of the pressurized fluid exerts the downwardly directed force F V  (arrow  170 ) upon the lower surface  168  to urge the valve member  110  against the seal  114  when the valve assembly is closed, as in  FIG. 1 . The total net force holding the valve member  110  on the seal  114  is thus generally equal to F B +F V . 
       FIGS. 5 and 6  show the piston  140  in conjunction with the valve member  110  during respective closed and open positions of the valve assembly  100 . While  FIG. 5  shows the piston  140  to be in a medial portion of the piston chamber  144 , the starting location of the piston  140  could be anywhere along the vertical extent of the chamber so long as the upper surface  157  of the piston head  142  is not in contact with the upper surface  166  of the chamber  144 . Preferably, the piston head  142  will be initially located near the lower surface  168  of the chamber  144 , as depicted in  FIG. 1 . 
     In  FIG. 5 , the piston head  142  divides the piston chamber  144  between a lower chamber portion and an upper chamber portion. The lower portion is filled with the pressurized fluid, and the upper chamber portion encloses atmospheric air vented to the surrounding atmosphere along the stem  146 . 
     As noted above, while in the closed position the inlet fluid will impart the aforementioned fluidic force  160  upwardly upon the piston  140 , in opposition to the compression force F C  of the pin  148 . This force is denoted as F P1  in  FIG. 5 . It will be contemplated that the setpoint pressure of the pressurized fluid that causes collapse of the pin  148  equates to an associated setpoint force F S . Because the valve remains closed, F P1  is necessarily less than F S  (i.e., F P1 &lt;F S ). 
     The spring  120  will impart the F B  downwardly directed bias force (arrow  172 ) upon the valve member  110 . A portion of the pressurized fluid will pass up into the lower chamber to impart the F V  downwardly directed force (arrow  170 ) upon the valve member  110 . While the valve remains closed, the F P1  force remains decoupled from the F B  and F V  forces. Thus, the full spring force F B  will be applied to retain the valve surface  112  against the seal  114  and no simmering will occur even if the working pressure (e.g., 150 psi) is very close to the set pressure (e.g., 152 psi). 
     In  FIG. 6 , the inlet fluid reaches a second, higher pressure that provides a fluidic force F P2  that is greater than the setpoint force F S  (F P2 &gt;F S ) and thus is sufficient to collapse the pin  148  (F P2 &gt;F C ). The piston  140  is driven upwardly so that the upper surface  147  of the piston head  142  contactingly engages the upper chamber surface  166  of the valve member  110 . At this point, the piston  140  and the valve member  110  become coupled together as a single unit, and the entire unit advances upwardly as the F P2  fluid force  160  overcomes the downwardly directed F B  spring force  172  (F P2 &gt;F B ). 
     It is contemplated that an upstream valve (not shown), such as a ported ball valve, can be provided in fluid communication with the inlet port  104  of the valve assembly  100 . This upstream ball valve will normally remain open when the valve assembly  100  is in the closed position depicted in  FIG. 1 . When it becomes necessary to reset the valve assembly  100  from the open position of  FIG. 2  back to the closed position of  FIG. 1 , the upstream ball valve can be manually closed, and the internal pressure in the valve assembly  100  can be vented to permit replacement of the damaged pin with a replacement pin. 
     Once the fluidic pressure has been reduced within the valve assembly  100 , the spring  120  will drive the valve member  110  back on the valve seat  114 . The piston  140  can be manually depressed down to the bottom of the piston chamber  144 . The nut  150  ( FIG. 1 ) can be removed, and the collapsed member  148  can be removed and replaced with a new collapsible member. The nut  150  can be reinstalled, and the upstream ball valve can be opened to return the valve assembly  100  to pressure service. 
     It will be appreciated that the various embodiments disclosed herein may provide a number of benefits over the prior art. The respective arrangement of the piston and the valve member decouples the valve member from the inlet fluid pressure, allowing the entire bias force supplied by the spring to maintain the valve member seated on the sealing member. 
     For example, if the spring is configured to supply 100 pounds of force against the valve member, this amount of force will be applied to maintain the valve closed, even if the fluidic pressure is close to setpoint. So long as the pressure of the fluid remains below the setpoint pressure, the pressure of the fluid is immaterial to the spring force, and will not operate to offset this spring force. 
     Indeed, the pressure of the fluid (so long as less than setpoint) may be used to further urge the valve closed as disclosed above for some embodiments. It is contemplated that the valve may be alternatively configured to be balanced in the closed position (by setting Z=X) so that the pressure of the fluid has no net effect upon the closed valve. Although not required, the spring and the collapsible member each may be individually set to operate at the desired setpoint pressure. 
     The various embodiments eliminate the need for the use of internally disposed collapsible members, such as rupture disks below the valve seat, and the associated requirement to sense and monitor the differential pressure thereacross. This also eliminates the need as in the prior art to disassemble the valve to access and replace a failed rupture disk or similar member after the valve assembly has been opened. Rather, the external location of the collapsible member in the various embodiments disclosed herein give an instant indication whether the valve has transitioned to the open position, and allows easy resetting of the valve in a matter of a few minutes. 
     The elimination of valve simmering provides significant environmental advantages, since small amounts of the pressurized fluid are not allowed to seep past the seal interface and contaminate the surrounding environment or interfere with downstream processing. 
     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. For example, the particular elements may vary depending on the particular environment without departing from the spirit and scope of the present invention.

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