Abstract:
A pressure relief valve and method of preparation is provided in which the relief valve includes a body having a seat disposed in a passageway. The relief valve also includes a piston sealing a gasket against the seat by a spring. The spring is adjusted and retained by an adjusting gland. The piston includes a cone that aids in reclosing the valve quicker than it would close without the cone. The relief valve has a low blowdown and may be easily assembled and then shipped on the same day.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention generally relates to relief valves and more specifically to a low blowdown relief valve used in the refrigeration and air conditioning industry that may be easily assembled and then shipped on the same day.  
           [0002]    Both refrigeration and air conditioning systems employ liquid/vapor mix refrigerant fluids that are under pressure. Under some circumstances, such as when operating controls fail or when the system is exposed to excessive heat, the pressure may build up to a value that is greater than normal operating pressure. If pressure were to build up high enough to cause the system to rupture, large quantities of liquid refrigerant would be released. The rupture would result in a sudden reduction of pressure so that the liquid released is vaporized almost instantly, with explosive results.  
           [0003]    To release the refrigerant at a controlled rate and to maintain a safe pressure within refrigeration and air conditioning systems, each system includes several pressure relief valves. A pressure relief valve is a pressure-actuated valve held closed by a spring and designed to automatically relieve at a predetermined pressure. The most popular type of relief valve is the direct-spring-loaded pop-type. In this type, a piston housed in a body conventionally contains a Teflon seat disc that is urged to seal against a valve seat at a set pressure by a spring whose compression is controlled by an adjusting gland.  
           [0004]    At the relief valve setting, the set pressure force exerted by the spring is equal to the force exerted by, for example, a refrigerant pressure. As the system pressure increases above the setting, the valve will begin to seep until there is enough flow to pop the piston open and provide full discharge. The pressure above the setting at which the piston is fully open depends upon the valve design. Since the flow rate conventionally is measured at a pressure of 10% above the setting, it is necessary that the valve reliably open within this 10%. This requirement is set out in American Society of Mechanical Engineering (ASME) Standard, Section VIII Div I, sec UG 131, para c1.  
           [0005]    Pressure relief valves are designed to reclose automatically. This is done at a predetermined reclosing pressure after the valve has discharged so as to only expel a measured volume of fluid. The ratio of the difference between the set pressure and the reclosing pressure to the set pressure is called the blowdown. As the percentage by which the reclosing pressure is maintained below the set pressure increases, the amount of gas or vapor that is discharged from a refrigeration or air conditioning system increases. The blowdown will vary with the valve design and is between 40% to 60% for most conventional pop-type relief valves.  
           [0006]    In addition to a high discharge capacity, the advantages of a conventional pop-type relief valve are generally understood to be simplicity of design and low initial cost. However, the basic design of these valves has not been improved upon in the past 40 years. This has lead to problems in manufacturing, assembly, and operation so as to remove simplicity of design and low initial cost advantages.  
           [0007]    By themselves, the number of parts of conventional relief valves makes it difficult to assemble the valve. Many of these parts require dedicated features to be machined into the interior cavity of the relief valve body. Machining the relief valve body is difficult and expensive.  
           [0008]    The seat disc of conventional pressure relief valves causes other problems. Generally, the synthetic rubber seat disc typically is made of Teflon. Properly installing a Teflon seat disc requires a long processing time, which, in turn, results in an increase in the initial cost of the valve. Although most manufacturers use polymers such as virgin Teflon or other filled grades as a function of the application, some manufacturers use 100% neoprene seat discs. Although neoprene is easier to set, neoprene tends to degrade over time when exposed to refrigerant.  
           [0009]    A Teflon seat disc requires operators to engage in a time-consuming two-step process. First, the operator must assemble the valve and preload the seat disc with the spring to a set pressure so as to allow the Teflon to take an initial set. After 24 hours, the operator must then check the set pressure of the valve to determine whether the set pressure is at the desired set pressure. If the operator is required to readjust the set pressure, the operator will turn the adjusting gland so as to further compress the spring. Either way, the operator will again verify that the set pressure of the valve is within the design set pressure tolerance after  24  more hours.  
           [0010]    After this 48 hour process, the relief valve may be ready for shipment to a customer. However, not only are conventional pressure relief valve designs difficult to set, it is very difficult to ensure repeat set and pop performance that is in compliance with Standard 15 of the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). The unreliable set pressure and pop pressure creates time-consuming problems at the American National Standards Institute National Board (ANSI NB) testing lab and results in high scrap rates. Even if the relief valve is ready for shipment to a customer after 48 hours, this long production lead-time creates a variety scheduling problems.  
           [0011]    As noted above, the blowdown is between 40% to 60% for most conventional pop-type relief valves. However, recent pending European regulations seek to minimize refrigerant discharge and now require employed relief valves to have a blowdown of not greater than 10%. Thus, there is a need for a low blowdown ratio relief valve used in the refrigeration and air conditioning industry that may be easily assembled and then shipped on the same day.  
         SUMMARY OF THE INVENTION  
         [0012]    A pressure relief valve and method of preparation is provided in which the relief valve includes a body having a seat disposed in a passageway. The relief valve also includes a piston sealing a gasket against the seat by a spring. The spring is adjusted and retained by an adjusting gland. The piston includes a cone that aids in reclosing the valve quicker than it would close without the cone. The relief valve has a low blowdown and may be easily assembled and then shipped on the same day. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is an elevation sectional view of a valve  100 .  
         [0014]    [0014]FIG. 2 is a plan view of the piston  200 .  
         [0015]    [0015]FIG. 3 is a sectional view of the piston  200  taken generally off of line  3 - 3  of FIG. 2.  
         [0016]    [0016]FIG. 4 is a bottom view of the piston  200 .  
         [0017]    [0017]FIG. 5 is an enlarged view of the groove  204  taken generally off of line  5  of FIG. 3.  
         [0018]    [0018]FIG. 6 is a plan view of the gasket  300 .  
         [0019]    [0019]FIG. 7 is an elevation view of the spring  400 .  
         [0020]    [0020]FIG. 8 is a bottom view of the adjusting gland  500 .  
         [0021]    [0021]FIG. 9 is a sectional view of the adjusting gland  500  taken generally off of line  9 - 9  of FIG. 8.  
         [0022]    [0022]FIG. 10 is a block diagram of the production process  600  of the invention.  
         [0023]    [0023]FIG. 11 is a block diagram of the operation process  700  of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    The present invention relates to relief valves and can be employed in a wide variety of constructions and arrangements. While several of such arrangements are illustrated herein, there are numerous other embodiments and constructions in which the present invention can be realized. Other arrangements will be apparent to a person of skill in the art from the following description of the preferred embodiments.  
         [0025]    [0025]FIG. 1 is an elevation sectional view of a valve  100 . The valve  100  may be referred to as a relief valve or as a pop-type relief valve. The valve  100  may also be referred to as a safety valve or an escape valve. In general, the valve  100  may be any pressure-actuated valve that is held closed by an elastic force and adapted to automatically relieve at a predetermined set pressure.  
         [0026]    The valve  100  may be adapted to be mounted to a vessel that is designed to operate under pressure. Although the vessel may be part of a refrigeration system or an air conditioning system, the valve  100  may be used in any system where there is a need to release a fluid under pressure, such as steam, air, liquid, and gas/vapor, and to maintain a safe pressure within the system. To aid in adapting the valve  100  to be mounted to a vessel, the valve  100  may include a body  102 .  
         [0027]    The body  102  may be a rigid structure against which other parts may be registered. In one embodiment, the body  102  may be made from at least one of brass, cast iron, carbon steel, and stainless steel. The material of the body  102  may be a function of the set pressure at which the valve  100  relieves. The set pressure for the valve  100  may range about from 10 through 45 kilograms per square centimeter (KPSC) (150 through 625 pounds per square inch (PSI)). Depending on the material composition, the valve  100  may be made from a non-metallic material, such as plastic.  
         [0028]    The body  102  may define an interior  104  and an exterior  106 . The interior  104  may define a passageway  108  that is comprised of an inlet  110  and an outlet  112 . Sonic flow may be thought of as the maximum flow of a fluid through a valve for a given inlet where a minimum orifice cross section of the inlet largely dictates the flowrate; that is, for a fluid moving at sonic flow the flow will not increase even if the outlet or “set” pressure is reduced. The passageway  108  may include an annular cavity that substantially permits a sonic flow from the inlet  110  through the outlet  112 . Flow at the outlet  112  may be subsonic due to an increase in the cross sectional area of the passageway  108  at that location.  
         [0029]    To aid in mounting the body  102  to a vessel, the body  102  may include threads  114 . The threads  114  may be dry-seal threads that allow for joining without sealants. In one embodiment, the threads  114  may be ½″-14 National Standard Free-Fitting Tapered Mechanical Pipe Threads (NPTF). The threads  114  may be male threads that extend along the exterior  106  to a surface  116 . The surface  116  may meet the inlet  110  at a furthest most end of the body  102 .  
         [0030]    The body  102  may further include an orifice  118  and a seat  120 . The orifice  118  may extend from the surface  116  to the seat  120  as part of the passageway  108  as defined by a diameter  122 . The seat  120  may be a flat surface having a fine tool finish against which a gasket may seal. In one embodiment, the seat  120  may be about 1.3 centimeters (cm) (½ inch (″)).  
         [0031]    Radially outward from the seat  120  may be an elbow  124 . The elbow  124  may be an annular ring disposed as a feature of the interior  104  that widens the dimensions of the passageway  108 . Immediately radially outward of the elbow  124  may be a surface  126 . The surface  126  may extend as part of the passageway  108  to a seat  128 . The seat  128  may be disposed between a surface  126  and threads  130 . The threads  130  may be female Unified inch screw threads such as 1-{fraction (5/16)}″-28 UN having a class 2B internal thread pitch diameter tolerance.  
         [0032]    The threads  130  may extend as part of the passageway  108  to a surface  132 . Similar to the surface  126 , the surface  132  may extend as part of the passageway  108 . A height of the surface  132  may be equal to or greater than a thickness of a base  502  of an adjusting gland  500  (FIG. 1 and FIG. 9). In assembling the valve  100 , the surface  132  may act as a guide for the adjusting gland  500  while a spring  400  (FIG. 1 and FIG. 7) is uncompressed. In one embodiment, the height of the surface  132  of FIG. 1 is about 0.16 cm ({fraction (1/16)} inches) greater than the thickness of the base  502 .  
         [0033]    Immediately radially outward of the surface  132  may be threads  134 . The threads  134  may be female threads that form the remainder of the passageway  108  and may be used to couple the valve  100  to other structures. In one embodiment, the threads  134  may be 1¼″-11.5 NPTF.  
         [0034]    The body  102  may include a surface  136  as the most remote feature from the surface  116 . The exterior  106  may be disposed between the surface  116  and the surface  136  to define a height  138 . Moreover, the exterior surface  106  may include a stop  140  and a jog  142 . The stop  140  may be disposed approximately at a distance of a stop height  144  from the surface  116  such that a ratio of the height  138  to the stop height  144  may be approximately 4.8:1.0. The jog  142  may be disposed approximately at a distance of a jog height  146  from the surface  116  such that a ratio of the jog height  146  to the stop height  144  may be approximately 2.0:1.0.  
         [0035]    To adapt the valve  100  to be held closed by an elastic force and to automatically relieve at a predetermined set pressure, the valve  100  may further include a piston  200 , a gasket  300 , and the spring  400  and the adjusting gland  500  mentioned above.  
         [0036]    [0036]FIG. 2 is a plan view of the piston  200 . FIG. 3 is a sectional view of the piston  200  taken generally off of line  3 - 3  of FIG. 2. FIG. 4 is a bottom view of the piston  200 . Conceptually, the piston  200  may be any piece that slides within the interior  104  of the body  102  and that is adapted to move under fluid pressure.  
         [0037]    The piston  200  may include a cone  202 , a groove  204 , and a ring  206 . The cone  202  may be thought of as a nose cone. Moreover, the cone  202  may be a forwardmost section of the piston  200  that includes a cone surface  208 . The piston  200  may define an axis  210  such that the cone  202  may be defined with respect to the axis  210 .  
         [0038]    In operation, the cone surface  208  first may experience static fluid forces and then dynamic fluid forces in addition to the static fluid forces. Reducing the dynamic forces of an applied fluid on the piston  200  works to reduce the difference between the static fluid force required to open the piston  200  and the dynamic fluid force required to close the piston  200 . The cone surface  208  may be shaped to offer minimum fluid dynamic resistance so as to reduce the dynamic forces of an applied fluid on the piston  200 . Put another way, forces on the piston  200  are essentially static up until a point where the valve  100  pops open. Where dynamic forces are generated by fluid impinging on the cone  202 , the dynamic forces are reduced significantly by the cone  202  as compared to a flat piston surface that conventionally faces such dynamic forces. This reduction, in turn, creates a reduction between the fluid force needed to open the piston  200  and the fluid force at which the piston  200  recloses. In other words, the elastic force provided by the spring  400  now quickly overcomes the fluid force to reclose the piston  200  due to the addition of the cone  202  to the piston  200 . Thus, rather than a blowdown of 40% to 60% as in the conventional pop-type relief valve, the valve  100  is characterized by a blowdown of not greater than 10%.  
         [0039]    A Mach number represents a ratio of the speed of an object, body, or projectile (Vp) to the speed of sound (c) in a surrounding, relatively stationary medium. For example, an aircraft moving twice as fast as the speed of sound is said to be traveling at Mach 2. An aircraft moving as fast as the speed of sound is said to be traveling at Mach 1.  
         [0040]    Drag represents resistance of motion of a projectile through a fluid. For example, a bullet traveling through air experiences resistance to its forward motion due to the air. Drag may be represented in a drag coefficient (CD), where the drag coefficient is the ratio of the drag (D) on a projectile moving through a fluid to the product of the velocity (Vp) and the surface area (Ap) of the projectile. For a flat surface of a cylinder projectile passing through a relatively stationary fluid at Mach 1, the drag coefficient is 1.0. If a round -nose projectile were to pass through this same fluid, the drag coefficient drops to around 0.30. Where a sharp-nose projectile is used, the drag coefficient drops to around 0.25. In other words, as the face of the projectile becomes more streamlined, the resistance to the motion of the projectile passing through the fluid decreases.  
         [0041]    One reason for the drop in drag coefficient may be due the separation of the X and Y reaction force (F) components on the projectile. For a flat faced projectile, the horizontal force component (F X ) represents 100% of the reaction force and the vertical force component (F Y ) represents zero of the reaction force. Where the face of the projectile is shaped to be symmetrically streamline, the horizontal force component (F X ) reduces from representing 100% of the reaction force and the vertical force component (F Y ) increases. Since the streamline of the projectile is symmetrical, the projectile experiences evenly distributed vertical force components (F Y ) that cancel each other out. The overall effect works to decrease the resistance to the motion of projectile passing through the stationary fluid.  
         [0042]    Rather than dealing with an aircraft or bullet moving through air at Mach 1, the inventor of this invention was faced with the problems associated with high pressure, confined refrigerant vapor passing over a flat faced piston of a pop-type pressure relief valve at approximately sonic velocity. In particular, the inventor was faced with reducing the blowdown ratio for such a relief valve used in the refrigeration and air conditioning industry while ensuring that the relief valve was easy to assemble and ship on the same day.  
         [0043]    A round-nose shape or a sharp-nose shape may define the cone surface  208 . In one embodiment, passing a line through a fixed vertex point and moving the line along a fixed directrix curve may generate the cone surface  208 . Although a straight line generated the cone surface  208  shown in FIG. 3, the passed line may be a curved or other shaped line. Alternatively, the cone surface  208  may be defined by an angle  212  as measured between the cone surface  208  and the axis  210 . In one embodiment, the angle  212  may be a value approximately from about 30 degrees through about 60 degrees. In another embodiment, the angle  212  may be 45 degrees, plus or minus 5 degrees with a fixed directrix curve having a diameter of 0.60 cm, plus or minus 0.15 cm (0.23 inches, plus or minus 0.05 inches).  
         [0044]    The groove  204  may be defined by a narrow channel having dovetail features that are adapted to retain the gasket  300  and prevent the gasket  300  from blowing out of the valve  100  along with any expelled fluid. FIG. 5 is an enlarged view of the groove  204  taken generally off of line  5  of FIG. 3. In one embodiment, the groove  204  may have a socket cross section shaped to tightly fit a bird&#39;s tail-spread so as to resist pulling the gasket  300  in all directions except one. The groove  204  may define a groove diameter  214 .  
         [0045]    As noted above, the piston  200  may include a ring  206 . The ring  206  may have an interior shape that defines part of the groove  204  and an exterior annulus shape that defines a ring diameter  216 . By way of explanation, increasing the diameter  216  with respect to the diameter  214  may cause the valve  100  to pop sooner. However, this will also increase the blowdown. Thus, to ensure that the piston  200  reliably pops at a predetermined pop pressure, it is desirable to minimize the ring diameter  216  with respect to the groove diameter  214 . In one embodiment, the ratio of the ring diameter  216  to the groove diameter  214  may be a value from 1.4 to 1.5. In another embodiment, the ratio of the ring diameter  216  to the groove diameter  214  is about 1.44.  
         [0046]    The diameter  216  may influence the blowdown. Blowdown is the difference between the pressure at which an applied static fluid force overcomes a force of the spring  400  (the set pressure) and the pressure at which the compression force of the spring  400  overcomes an applied dynamic fluid force (the reclosing pressure). As the percentage by which the reclosing pressure is maintained below the set pressure increases, the amount of gas or vapor that is discharged from a refrigeration or air conditioning system increases. Conventional blowdowns are between 40% to 60% for most pop-type relief valves.  
         [0047]    A blowdown target of 10% applies to 10% of valve rated pressure. Accordingly, for a set pressure of 400 pounds per square inch (PSI) and a blowdown of 10%, the valve reseats at 360 PSI (=400−(400)(10%)). To ensure a blowdown of no greater than 10%, it is important that the diameter  216  be made a function of the cone  202 . There are other factors that may need to be addressed. For example, the diameter  216  may need to be kept to a minimum to present a minimum projected area of jet on disc. Here, the diameter  216  is a function of the mechanical strength required to retain the O-ring  300  as the O-ring  300  expands radially outwards under pressure. A ratio of the diameter  216  to a seal diameter may range from 1.5 to 2.0 as determined through experimentation by the inventor of this invention. Moreover, although a higher value for the diameter  216  to a seal diameter ratio may help the pop action, such an increase in ratio will increase blowdown. Here, the cone  202  works towards streamlining the flow of the working fluid much like the atmospheric force a jet experiences on an inclined plane.  
         [0048]    Immediately radially outward from the ring  206  may be the shoulder  218 . The shoulder  218  may increase that surface area of the piston  200  that experiences the dynamic forces of an applied fluid. As best seen in  4 , the ring  206  and the shoulder  218  may define ports  220 . The ports  220  may work as exhaust ports to permit fluid to pass through an area of the piston  200 . To ensure that the piston  200  does not restrict the flow of fluid, the total cross sectional area of the ports  220  may be twice the total cross sectional area of the orifice  118  (FIG. 1) of the body  102 .  
         [0049]    The piston  200  may further include a guide  222  and a core  224 . The guide  222  may be an elevated peg structure about which the spring  400  may fit. The core  224  may aid in handling the piston  200  during manufacture of the piston  200 . Moreover, the core  224  may be used to maintain a uniform section thickness for injection molding where the piston  200  is made of an injection molded plastic.  
         [0050]    The piston  200  may be made of a thermoplastic polyamide having high strength, toughness, and resistance to abrasion, most chemicals, and repeated impact. In one embodiment, the piston  200  may be made of Zytel® nylon resin from Dupont, Inc. of Wihnington, Del. Alternatively, the piston  200  may be made of metal, such as brass. Where the piston  200  is made of metal, the piston  200  may be made of two individual pieces: the cone  202  and the remainder of the piston  200 . The piston  200  made of two individual pieces is shown in FIG. 1. A two-piece piston  200  may be required where it is difficult to machine the groove  204  as a dovetail groove.  
         [0051]    [0051]FIG. 6 is a plan view of the gasket  300 . To provide a snug fit within the groove  204  of the piston  200 , the gasket  300  may be in the shape of an O-ring. The O-ring may be a Teflon coated neoprene O-ring, such as a size 015 O-ring made of compound #3110-70 as manufactured by Parco, Inc. of Ontario, Calif. Teflon is a registered trademark for polytetrafluoroethylene, a white, waxy solid polymer. Use of a Teflon coated neoprene O-ring works to minimize setting problems associated with using an O-ring made completely of Teflon. This combination beneficially provides the resilience of neoprene with the chemical compatibility of Teflon.  
         [0052]    [0052]FIG. 7 is an elevation view of the spring  400 . The spring  400  may be an elastic body of any kind that is adapted to regulate the motion of the piston  200 . Examples of materials that may be used as part of an elastic body include steel, rubber, or compressed air. Although an example of the spring  400  may be a coil of wire, the spring  400  is not limited to this construction. In general, the spring  400  may be any elastic device that works to regain its original shape after being compressed. Where the spring  400  is a coil spring, the coil spring may include flat ground end surfaces so as to more evenly spread the forces between the spring  400  and surfaces against which it is mounted. The spring  400  may be made of music wire coiled for a KPSC setting about from 10 through 45 KPSC (150 through 625 PSI), such as the range set of 10 to 19, 20 to 26, 27 to 35, and 36 to 45 KPSC (150 to 274, 275 to 374, 375 to 499, and 500 to 625 PSI).  
         [0053]    [0053]FIG. 8 is a bottom view of the adjusting gland  500 . FIG. 9 is a sectional view of the adjusting gland  500  taken generally off of line  9 - 9  of FIG. 8. The adjusting gland  500  may include a base  502  and a guide  504 . Together, the base  502  and the guide  504  may work to adjust the set pressure of the spring  400  as well as permit the exhaust of liquid from the vessel against which the valve  100  may be mounted.  
         [0054]    The base  502  may be in the shape of an annular disk within which ports  506  may be disposed. Similar to the ports  220 , the ports  506  may work as exhaust ports to permit fluid to pass through an area of the adjusting gland  500 . To ensure that the adjusting gland  500  does not restrict the flow of fluid, the total cross sectional area of the ports  506  may be twice the total cross sectional area of the orifice  118  (FIG. 1) of the body  102 .  
         [0055]    Disposed about an exterior perimeter of the base  502  may be threads  508 . The threads  508  may male threads that mate with the threads  130  (FIG. 1) of the body  102 . In one embodiment, the threads  508  may be male Unified inch screw threads such as 1-{fraction (5/16)}″-28 UN having a class 2A external thread pitch diameter tolerance. As seen in FIG. 1, the guide  504  may cooperate with the guide  222  of the piston  200  to maintain a relatively straight alignment of the spring  400 .  
         [0056]    [0056]FIG. 10 is a block diagram of the production process  600  of the invention. At  602 , the body  102  may be presented. At  603 , the body  102  may be machined in one step. Fixing the body  102  within a lathe having opposing drills may perform machining the body  102  in one step. Other working tools designed to cut metal, such as a laser or high pressure water, may be used. A first drill profiled to hog out the passageway  108  from the surface  136  (FIG. 1) to the seat  120  may be inserted into the outlet  112  at the surface  136 . Simultaneously with the first drill, a second drill profiled to hog out the passageway  108  from the surface  116  and to form the threads  114  may be disposed about the surface  116 . The first drill may include a cavity to receive into it the second drill so as to ensure cylindrical machining about an elongated central axis of the body  102  that is within specified tolerances. Alternatively, the first drill may include a cutting blade to remove material from the inlet  110  to the surface  116 .  
         [0057]    In a most efficient form, the body  102  includes no more than five features: the seat  120 , the elbow  124 , the threads  130 , the inlet  110 , and the threads  114 . Where machining produces the body  102 , these five features may be referred to as machined features. Thus, the first drill and the second drill need only include blades to remove material from the body  102  to form the seat  120 , the elbow  124 , the threads  130 , the inlet  110 , and the threads  114 . Since the body  102  need only be machined to form five features, the body  102  is an inexpensive body to machine. Moreover, since only two working tools are needed to form the five features, the body  102  is a relatively easy body to machine. The body  102  also may be made from a single injection molding process.  
         [0058]    At  604 , the gasket  300  may be placed within the groove  204  of the piston  200 . At  606 , the spring  400  may be disposed about the guide  222  of the piston  200 . And at  608 , the guide  504  of the adjusting gland  500  may be placed within the spring  400  to form a controlling parts assembly.  
         [0059]    At  609 , the controlling parts assembly may be placed within the interior  104  of the body  102 . At  610 , the adjusting gland  500  may be rotated until the gasket  300  resides against the seat  120 . At  612 , a working force may be applied against the cone  202  of the piston  200  to measure the set pressure of the valve  100 . In one embodiment, the desired set pressure maybe from 10 through 45 KPSC (150 through 625 PSI).  
         [0060]    At  614 , an operator may wait for a setting time period to pass. In one embodiment, the setting time period is less than 24 hours. In another embodiment, the total setting time for each setting time period is less than 24 hours.  
         [0061]    At  616 , a decision is made in the production process  600 . If the measured set pressure is outside of the tolerance of the desired set pressure, than the production process  600  may return to step  610 . If the measured set pressure is within the tolerance of the desired set pressure, then production process  600  may continue to step  618 . Since a Teflon coated neoprene O-ring gasket replaces the Teflon sealing gasket in one embodiment, setting and resetting is made easier.  
         [0062]    At  618 , the adjusting gland  500  may be secured to the body  102 . The adjusting gland  500  may be secured to the body  102  by, for example, using a Loctite® 290 threadlocker product from Loctite Corporation of Rocky Hill, Conn. or by welding the adjusting gland  500  to the body  102  by tungsten inert gas (TIG) welding. At  620 , the valve  100  may be shipped within 24 hours of beginning step  602 . This is a short production lead-time cycle.  
         [0063]    [0063]FIG. 11 is a block diagram of the operation process  700  of the invention. For the operation process  700 , the set pressure is assumed to be about 21 KPSC (300 PSI). However, the set pressure may be any value according to the application of the valve  100 . Preferably, the valve  100  may react to refrigerant vapor or any other compressible fluid since, under some circumstances, if used with liquid only, the liquid may merely seep around the set pressure and the valve  100  may not fully pop open.  
         [0064]    At  701 , the valve  100  may be mounted to a vessel that is designed to operate under pressure by inserting the threads  114  of the body  102  into mating female threads and rotating the body  102 . At  702 , the gasket  300  (FIG. 1 and FIG. 6) may be urged against the seat  120  by the 21 KPSC (300 PSI) set pressure of the spring  400 . At  704 , a working fluid under pressure may enter the inlet  110  of the valve  100  to act upon the surface area of the cone  202  of the piston  200 .  
         [0065]    The working fluid may be refrigerant from an air conditioning system or refrigerant from a refrigeration system. Refrigerant may be a substance, such as air, ammonia, water, or carbon dioxide, used to provide cooling either as the working substance of a refrigerator or air conditioner or by direct absorption of heat. As other examples, the working fluid may be water, brine, or gas. In general, the working fluid is a function of the system into which the valve  100  is located. By way of example and not limitation, the working fluid will be referred to as refrigerant in FIG. 11.  
         [0066]    At  706 , the set pressure force exerted by the spring  400  may be equal to the force exerted the refrigerant pressure. Here, the pressure of the refrigerant only acts upon the surface area of the cone  202 . At  708 , the refrigerant pressure may increase slightly above the set pressure of the spring  400  so as to slightly raise the piston  200 . At  710 , refrigerant begins to seep around the gasket  300 . At  712 , the refrigerant pressure additionally acts upon the surface area of the gasket  300 , the ring  206  (FIG. 2), and the shoulder surfaces  218  of the piston  200 . Since the same pressure begins to act on an increased surface area, the amount of force applied against the spring  400  by the refrigerant increases (recall that force (F) equals pressure (P) times unit area (A) or F=PxA).  
         [0067]    When there is enough flow of the refrigerant, the increase in force acting against the spring  400  causes the piston  200  to pop open and provide full discharge at  714 . Due to the invention, the valve  100  reliably pops opens before the refrigerant pressure reaches 23 KPSC (330 PSI); that is, the valve  100  reliably pops opens before the refrigeration pressure is beyond 110% of the 21 KPSC (300 PSI) set pressure of spring  400 .  
         [0068]    The valve  100  efficiently discharges refrigerant due to a better sonic flow through the valve  100 . As the valve  100  discharges refrigerant, the refrigerant pressure decreases. When the refrigerant pressure decreases to a predetermined value, the valve  100  automatically recloses at  716 . Since the valve  100  is designed to open and close at predetermined fluid pressures, only a known, controlled volume of refrigerant is expelled from the system as a function of the system settings.  
         [0069]    Recall that the difference between the set pressure and the reclosing pressure is called the blowdown. The blowdown is about 40% to 60% for most conventional pop-type relief valves. For a conventional valve having a set pressure of 21 KPSC (300 PSI), the valve may close in this example when the refrigerant pressure drops to 11 KPSC (150 PSI). Here, due to the invention, the valve  100  reliably recloses before the refrigerant pressure reaches 19 KPSC (270 PSI); that is, the valve  100  reliably recloses before the refrigeration pressure is less than 90% of the 21 KPSC (300 PSI) set pressure of the spring  400 . Accordingly, the invention works to ensure that the blowdown of the valve  100  reliably is not greater than 10%.  
         [0070]    As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications that may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.