Abstract:
A hydraulically attenuated pressure relief valve incorporating a seal retainer disposed in the valve body and a valve member that is movable in a valve body between a position in contact with a seal to close the flowway therethrough and a second position above or apart from the seal to open the flowway. The seal retainer is restrained in the valve body by a body cap and engages the seal with sufficient energy to allow use of the valve in high pressure environments with improved seal function, durability, and maintainability. The pressure relief valve is designed without internal, wetted threads, thereby eliminating the possibility of leakage through the threads and/or damage to the valve body by erosion or washout of the threads.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to pressure relief valves and more particularly to valves that open at a rapid rate to relieve pressure conditions that exceed specifications which then re-seal when the pressure returns to specified operating conditions such that fluid flow through the flowway in the valve body is stopped and the valve can be re-set.  
         [0002]     Pressure relief valves are widely employed in pressurized systems to enhance safety and maintain system integrity. Typically, these valves are preset to open at a pressure approaching the system limits. Such limits may exceed 5000 psi pressures that exceed the design capability of pressure relief valves available until recently. Pressure relief valves that can operate at higher pressures must balance the pressure-generated forces on the valve member so as not to exceed design capabilities of the trip mechanism. This balancing is accomplished by the use of an additional pressure chamber above the valve member (see, for instance, U.S. Pat. No. 5,715,861). Generally, the higher the pressure, the greater the hydraulic forces in the system and thus the necessity for the valve to open quickly to relieve excess pressure and prevent failure or rupture. Proper functioning of the valve mechanism and valve pressure release, and the integrity of the valve seals, are critical concerns in such systems.  
         [0003]     Pressure relief valves that open at a rapid rate are typically employed in systems that encounter acute or transient pressure spikes in excess of the system operating or design limits. Depending upon the application, such valves may encounter these excess pressures on only limited occasions, or with recurrent frequency. When these excess pressures are encountered, the pressure relief valve must be able to open rapidly to prevent system failure or breach. In addition, as the operating pressure of the system increases, the forces acting upon the valve components increase, which can compromise valve function as a consequence of a loss of seal integrity.  
         [0004]     U.S. Pat. No. 5,715,861 reviews the limitations of the use of resilient materials to promote proper valve function in U.S. Pat. Nos. 2,973,776 and 2,973,777. The &#39;861 patent states that one effect of the use of such materials in these types of valves is an unintended opening and resetting cycle. This cycle could impair proper functioning of the valve or cause it to fail, thus compromising system integrity and safety. In response to these limitations, the &#39;861 patent incorporated a hydraulic shock absorption design in the valve body and bonnet to reduce or eliminate the potentially destructive effect of these forces on the valve.  
         [0005]     A pressure relief valve piston or valve member exposed to system pressure will only encounter the rapid acceleration—deceleration forces discussed above during an excess pressure relief event. However, it is not only important that the pressure relief valve work properly during an excess pressure event, but also that it not leak during normal system operation. Typical pressure relief valves are constructed with seals of resilient materials positioned at the interface between the component parts of the valve to resist fluid leakage. Loss of valve integrity by rupture or other failure of a seal impairs system integrity and safety.  
         [0006]     The above-identified &#39;776 and &#39;777 patents disclose the use of an annular seal ring surrounding the valve member in the closed position. No other seals around the valve member stem or bushing are indicated. Pressures around the stem when the valve opened were apparently not a significant consideration of the design, or it was assumed that those skilled in the art would realize that a seal was not necessary at such locations.  
         [0007]     The presence of a pressurized chamber above the relief port opening member/piston when the valve is opened or closed requires an additional piston seal and stem seal in the valve shown in the &#39;861 patent to reduce leakage of fluid from the enclosed chamber. Whereas the focus of the &#39;861 patent is on attenuation of the initial rapid movement of the relief port opening member/piston as the piston approaches its limit of travel while minimizing rebound forces into the movement of the piston, the focus of the present invention is (1) improving seal function, durability, and maintainability and (2) eliminating the possibility of leakage through threads. The seals of such valves must withstand normal system operating pressure; failure of the seals would no longer provide an enclosed chamber and fluid would escape either through the outlet port or through the stem bushing and bonnet. The &#39;861 design uses a stem bushing in a bonnet to define an upper surface of the enclosed chamber. Excessive pressures, or physical damage to the bonnet assembly, could deform the stem bushing at the interface with the valve body and piston stem, thereby allowing significant loss of fluid under pressure.  
         [0008]     Additional limitations of these prior designs include the use of a threaded member to engage the seal at the lower end of the valve member or valve member head of the &#39;861 and &#39;777 patents and the use of the inflow line conduit to compress the lower valve member seal in the &#39;861 patent. In addition, both the &#39;777 and &#39;861 patents utilize threads to rotate the conduit or nut into position to engage the seal (note that the nut can be disengaged from the body by the installer and expose the valve member seal). If the conduit or nut mating surface is damaged or otherwise does not meet the specification required for mating with the seal surface, a seal failure and possible damage to the valve member could occur. Note also that the torque used by the installer could excessively compress and damage the seal also causing failure.  
         [0009]     It is, therefore, an object of the present invention is to provide a hydraulically cushioned pressure relief valve where fluid leakage at component interfaces is minimized.  
         [0010]     It is a further object of the present invention to minimize fluid leakage from the pressurized chamber by the use of a design that enables the use of stronger, more durable, more easily replaceable seals within the valve body.  
         [0011]     It is a further object of the present invention to define one or more surfaces of the enclosed chamber by incorporation of a seal retaining mechanism.  
         [0012]     It is a further object of the present invention to provide a pressurized chamber that does not utilize the surface of a stem bushing or other component of the bonnet to define the chamber.  
         [0013]     It is a further object of the present invention to provide a valve in which the lower valve member seal is not engaged by rotation using a screw thread, and not subject to significant rotational torque forces during installation.  
         [0014]     It is a further object of the present invention to provide a valve in which the seals are easier to install and replace compared to known prior pressure relief valves, allowing the use of stronger, more durable seal material(s).  
         [0015]     It is a further object of the present invention to provide a valve in which the base or sub is bolted to the body, thereby reducing or eliminating the possibility of damage to the seal and valve member during installation.  
         [0016]     Yet another object of the present invention is to improve seal retainability and also provide ease of access for maintenance or replacement of the seals.  
         [0017]     Other objects, and the advantages of the present invention, will be made clear to those skilled in the art by the following description of the embodiments thereof  
       SUMMARY OF THE INVENTION  
       [0018]     In accordance with the present invention, these objects are achieved by providing a hydraulically cushioned pressure release valve incorporating a seal retainer to retain and engage seals at the valve member head and valve member stem. The seal retainer also defines the interior wall of an enclosed pressurized chamber, the lower wall of the chamber being defined by the upper surface of the valve member head. The seal retainer is located and retained in the valve body by a body cap on which bonnet assembly is also located.  
         [0019]     In another aspect of the invention, a pressure relief valve is provided comprising a valve body having an inlet and an outlet defining a passage for fluid flow therethrough and a body cap releasably engaged to the body. A valve member is disposed in the body and comprises a head with at least one fluid flow passageway therethrough for providing fluid communication between the inlet port and the enclosed chamber and a stern, the valve member being movable between a first position disposed in fluid flow-blocking relationship between the inlet and outlet of the body and a second position removed from the first position. A seal retainer is positioned in the valve body and at least partially defines an enclosed chamber. The seal retainer is retained in the body by the body cap for retaining a seal therein for sealing against the stem of the valve member; and a bonnet is attached to the cap with the stem of the valve member extending into the bonnet into engagement with means for selectively disengaging the stem to allow the valve member to move to the second position and for engaging the valve member to urge the valve member into the first position.  
         [0020]     In another aspect of the invention, the seal at the lower end of the closed valve member is located and engaged in the body by a separate base or sub attached to the body. This base portion also provides a connection to the inlet of the flowway through the body.  
         [0021]     In another aspect of the invention, a method is provided for relieving excess fluid pressure using a pressure relief valve in a pressurized system, the pressure relief valve comprising a valve body and a valve member movable within a flowway in the valve body from a first position closing the flowway to a second position opening the flowway when pressure exceeds a pre-selected pressure. The method comprises the steps of allowing a portion of the fluid in the flowway to pass through a passage in the head of the valve member into an enclosed chamber above the head of the valve member, retaining a seal in engagement with the outside diameter of the head of the valve member with a seal retainer, retaining the seal retainer in the valve body with a body cap attached to the valve body, the body cap bearing the force resulting from the pressure of the fluid in the enclosed chamber and the valve member bearing the force resulting from the pressure of the fluid in the flowway, and moving the valve member from the first position to the second position when fluid pressure in the flowway exceeds a pre-selected pressure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a longitudinal sectional view of one embodiment of a pressure relief valve constructed in accordance with the teachings of the present invention;  
         [0023]      FIG. 2  is a longitudinal sectional view of the pressure relief valve of  FIG. 1  taken along the line A-A in  FIG. 1 ;  
         [0024]      FIG. 3  is a longitudinal sectional view of the pressure relief valve of  FIG. 1  showing the valve member in the open position;  
         [0025]      FIG. 4  is a longitudinal sectional view of the pressure relief valve of  FIG. 1  taken along the same line as  FIG. 2  showing the valve member the open position;  
         [0026]      FIG. 5  is a longitudinal sectional view of a second embodiment of a pressure relief valve constructed in accordance with the teachings of the present invention in which the reference numbers are the same as  FIGS. 1 and 2 ; and  
         [0027]      FIG. 6  is a longitudinal sectional view of the pressure relief valve of  FIG. 5  taken along the line A-A in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     In one embodiment of a pressure relief valve constructed in accordance with the teachings of the present invention and shown in  FIGS. 1-4 , the valve  10  will be seen to comprise a base or sub  11  bolted or otherwise secured to the body  12 , a moveable valve member  13  disposed in the body  12 , a body cap  14  bolted or otherwise secured to the body  12 , and a bonnet  15  bolted or otherwise secured to the body cap  14 .  
         [0029]     An advantage of the present embodiment is that the body cap  14 , connected to the body by a plurality of fasteners, bears the upward force exerted by the pressure of the fluid in flowway  30  and enclosed chamber  42  (see infra) rather than the bonnet  15 . Thus, the body cap can be varied in dimension and attachment configuration as forces and design specifications require. In the present embodiment, body cap  14  is attached to valve body  12  with eight bolts. Another fastener design could be studs threaded into the body  12 , requiring only the removal of nuts for disassembly. In addition, use of body cap  14  in the present embodiment enables improved access to the seals located in valve body  12 . Another advantage of the present embodiment is that the bonnet assembly  15  is attached to the body cap  14  and not the body  12 .  
         [0030]     The base or sub  11  having a flowway  16  therethrough, an inlet  17  to the flowway  16  formed to receive inflow, an outlet  18  therefrom formed to mate with body  12 , and a flange  19 . The flange  19  having an upper surface  20  in contact with a lower surface  21  of body  12 . One or more passages  23  are provided through flange  19  at an approximate right angle to the flange upper surface  20  to receive a bolt  24 , stud, or other securing member. Bolt  24  inserts through passage  23  and attaches to the body  12  in threaded recess  29 , thus securing the base or sub  11  to the body  12  thereby causing the flange sealing member  22  to engage the flange upper surface  20  and the body lower surface  21 .  
         [0031]     The valve body  12  having a flowway  30  comprising a base port  31  or counterbore adapted to receive base outlet  18 , discharge port  32 , and discharge outlet  33 . A first, lower sealing member  34  is disposed in a counterbore (not numbered) formed in body  12  between base outlet  18  and body  12 . A raised surface (not numbered) is formed on the outlet  18  of base/sub  11  to energize lower sealing member  34  into engagement with the outside diameter (O.D.) of the head  35  of valve member  13 . Valve member  13  is movable in valve body  12  from a first, closed position in which first sealing member  34  seals against head  35  to close the flowway as shown in  FIGS. 1 and 2 , and a second position above or apart from first sealing member  34  to open flowway  30  as shown in  FIGS. 3 and 4 .  
         [0032]     Valve member  13  has a head  35 , a stem  36  extending from said head  35 , a stem end  37 , an upper surface  38  comprised of the difference between the O.D. of stem  36  and the O.D. of head  35 , and a lower surface  39  facing flowway  16 . Stem  36  extends from head  35  through a seal retainer  40  and body cap  14  to reversibly attach with a pin  41  or other attachment to bonnet  15 . The upper surface  38  of head  35  is the lower wall of the enclosed chamber  42  further defined by the inner wall  43  of the seal retainer  40 . One or more passages  44  are provided through the head  35  of valve member  13  to allow fluid from flowway  16  into enclosed chamber  42 , thereby providing a confined fluid volume at flowway pressure. The importance of this confined fluid volume is apparent when the flowway  16  pressure exceeds the release pressure setting of the bonnet  15 , at which time valve member  13  moves to the open position as shown in  FIGS. 3 and 4 , allowing fluid flow from base flowway  16  through body flowway  30  to the discharge port  32 . As the valve member  13  moves in response to the release by the bonnet, the presence of the fluid in the confined fluid volume in the enclosed chamber  42  restricts the rate at which the valve member  13  moves since the fluid in this enclosed fluid volume must exit through passages  44  against initial flowway  16  pressure to allow the valve member to occupy the enclosed chamber  42  and open the flowway, thus absorbing and reducing the acceleration and deceleration forces encountered by valve member  13  in releasing pressure.  
         [0033]     The seal retainer  40  is removably held in place by contact of its outer surface  45  with a counterbore  46  in the body  12 , and its upper surface  47  with a counterbore  48  in the body cap  14 . A raised surface  49  is formed on the seal retainer end  50 . A second, middle sealing member  51  is held in place in a counterbore in body  12  by seal retainer  40 , and energized by the raised surface  49  and the seal retainer end  50 .  
         [0034]     The body  12  having an upper surface  52  in contact with a lower surface  53  of body cap  14 , one or more passages  54  are provided through body cap  14  at an approximate right angle to the body upper surface  52  to receive a bolt, stud, or other securing member  24 . Bolt  24  inserts through said body cap passage  54  and attaches to the body  12  in recess  29 , thus securing the body cap  14  to the body  12 . A raised surface  55  is formed on the seal retainer  40  around the stem  36 . A third, upper sealing member  56  is disposed in a counterbore (not numbered) in body cap  14  between said raised surface  55  of the seal retainer  40  and the body cap  14  and energized by said raised surface  55  to seal against stem  36  to restrict fluid leakage. The bonnet  15  may be reversibly attached to the upper surface  57  of the body cap  14  and engages the stem  36  at pin  41  to retain valve member  36  in the flowway  30 . In a third embodiment shown in  FIGS. 5 and 6 , seal retainer  40  is formed without the raised surfaces  49  and  55 , creating the opportunity to use a different type of seal between the O.D. of head  35  and the inner diameter (I.D.) of flowway  30  and the O.D. of stem  36  and the I.D. of body cap  14 , respectively.  
         [0035]     Those skilled in the art who have the benefit of this disclosure will recognize from the foregoing description of the present invention that valve  10  can be opened by backing bolts  24  out of threaded recesses  29  in body  12  so that body cap  14  and seal retainer  40  can be removed from body  12 . By removing body cap  14  and seal retainer  40  in this fashion and by removing base/sub  11  from body  12  in the same fashion, the upper, middle, and lower seals  56 ,  51 , and  34 , respectively, are easily accessed, facilitating their replacement when valve  10  is refurbished. Further, because of the ease of access to upper, middle, and lower seals  56 ,  51 , and  34 , respectively, provided by the design of valve  10 , it is easier to insert and seat the seals in valve  10  than it is to insert and seat the seals in conventional, known pressure relief valves. It is not uncommon, for instance, that some seals must be rolled or otherwise deformed for insertion into the valve body of conventional pressure relief valves, creating the possibility of damaging the seal, and even once inserted into the valve body of known prior pressure relief valves, it can be difficult to seat the seal in its respective seal groove. It will also be apparent to those skilled in the art who have the benefit of this disclosure that, because the seals need not be folded, rolled, or otherwise deformed in order to insert into the body  12  of the valve  10  of the present invention, it is possible to utilize seals comprised of harder materials to better withstand the pressure and/or flow of the fluid in flowway  30 . In addition to known, commercially available seals, seals that may be used to advantage in connection with the valve  10  of the present invention include U-cup seals, V-spring energized seals, and so-called polyseals. Although not required, it is even possible to use metal-backed seals in connection with the valve  10  of the present invention for added durability and resistance to pressure. For these reasons, and because of the design of the pressure relief valve  10  of the present invention, the valve  10  may be advantageously used in high pressure applications.  
         [0036]     The pressure relief valve  10  embodying the present invention also includes means incorporated in the bonnet  15  for urging the valve member  13  into the first, closed position as shown in  FIGS. 1 and 2 , and means for resetting valve member  13  to the first, closed position after the valve member moves to the second position out of flowway  30  shown in  FIGS. 3 and 4 . Such reset mechanisms are known in the art and therefore not described in detail herein.  
         [0037]     Those skilled in the art who have the benefit of this disclosure will recognize that certain changes can be made to the component parts of the apparatus of the present invention without changing the manner in which those parts function to achieve their intended result. All such changes, and others that will be clear to those skilled in the art from this description of these embodiments of the invention, are intended to fall within the scope of the following, non-limiting claims.