Abstract:
A surge relief valve comprising a main valve body having a dome port and an inlet port. The inlet port is in fluid communication with a first fluid. The invention further includes a dome reservoir connected to the main valve body via the dome port and arranged to hold a second fluid, and a piston located in the main valve body, the piston in fluid communication with the reservoir, wherein the first fluid exerts an upward force on the piston, the second fluid exerts a downward force on the piston, and the piston is arranged to move in response to a differential in the upward and downward forces, wherein the first and second fluids are isolated from one another.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a surge relief valve in a safety relief system for a pressure vessel, more particularly to an improved surge relief valve for use in liquid product pipelines, and, even more particularly, to a surge relief valve having a dome gas-filled reservoir arranged to bias the main valve closed until a set relief pressure is sensed, and then to open to relieve the overpressure, and finally to force the main valve to close when the overpressure has dissipated. The present invention is an improvement over the invention disclosed and claimed in U.S. Pat. No. 5,842,501, issued Dec. 1, 1998, and incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     Heretofore, pilot operated safety relief valves have been provided in pressure relief systems. Examples of prior art pilot operated relief valves are disclosed in U.S. Pat. No. 4,848,397 dated Jul. 18, 1989, and U.S. Pat. No. 5,842,501, dated Dec. 1, 1998. While these types of relief valves have proven effective in applications where the fluid product is a gas, they are not suitable for use in some liquid applications, e.g., oil supply lines.  
         [0003]     Liquid product pipelines must be protected from liquid surge, typically caused by pump failure, rapid block valve closing, non-return check valve hard shutting, emergency shut down of a tank or loading system, or even a pump coming on or tripping. The magnitude of surge pressures vary—some are virtually undetectable, while others are severe enough to cause major damage. These propagating waves, either increasing or decreasing rapidly, are commonly known as hydraulic transient surges or water hammers that can cause severe damage to liquid product pipelines, vessels, flanges, valving, and associated equipment. Pilot operated safety relief valves don&#39;t operate quickly enough to open and relieve the pressure.  
         [0004]     What is needed, then, is a surge relief valve in a pressure relief system for a pressure vessel, more particularly an improved surge relief valve for use in liquid product pipelines, and, even more particularly, a surge relief valve having a dome gas-filled reservoir arranged to bias the main valve closed until a set relief pressure is sensed, and then to open to relieve the overpressure, and finally to force the main valve to close when the overpressure has dissipated.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention broadly comprises a surge relief valve comprising a main valve body having a dome port and an inlet port. The inlet port is in fluid communication with a first fluid. The invention also comprises a dome reservoir connected to the main valve body via the dome port and arranged to hold a second fluid, a piston located in the main valve body, the piston in fluid communication with the reservoir, wherein the first fluid exerts an upward force on the piston, the second fluid exerts a downward force on the piston, and the piston is arranged to move in response to a differential in the upward and downward forces, wherein the first and second fluids are isolated from one another.  
         [0006]     It is a general object of this invention to provide a surge relief valve assembly for rapid relief of excess pressure in liquid systems, whereby main valve set pressure and closing pressure are established solely by a fixed pressure of a suitable gas present in the dome region of the main valve, and whereby system relief can commence at the instant that system fluid pressure acting on the main seat area results in a force on the main piston greater than the opposing force exerted by dome gas pressure at the top of the piston.  
         [0007]     Another object of this invention is to provide a surge relief valve assembly with a dome gas reservoir permanently attached to the top cover plate (cap), whereby existing dome gas present when the main valve first starts to open can further be compressed in a controlled manner as the main valve piston opens, so as to regulate the piston stroke and ultimately force closed the piston when the process liquid overpressure condition abates.  
         [0008]     It is a further object of this invention to provide a surge relief valve that uses a main valve body in which the inlet passage is axially aligned with the main closure member (piston and seat), and where the outlet passage is aligned at ninety degrees to the inlet passage.  
         [0009]     A further object of the invention is to dampen main valve piston movements, particularly upon closing, and eliminate or reduce the incidence of piston oscillations within the surge relief valve through the use of a nonmetallic wedge ring that bears on the piston liner with pressure-induced frictional forces.  
         [0010]     Other objects, features, and advantages of the invention will be apparent from the drawings, specification and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a side elevational view of the surge relief valve assembly of the present invention;  
         [0012]      FIG. 2  is a top plan view of the surge relief valve shown in  FIG. 1 ;  
         [0013]      FIG. 3  is an enlarged sectional view of the surge relief valve shown in  FIGS. 1 and 2 , for illustrating the main relief valve in normal operating condition with the surge relief valve member in a closed position blocking flow from the pressure vessel;  
         [0014]      FIG. 4  shows the surge relief valve assembly of  FIG. 3  in a closed position; and,  
         [0015]      FIG. 5  shows the surge relief valve assembly of  FIG. 3  in an open position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     In the description that follows, the terms “upwardly” and “downwardly” are relative, and refer to the perspective on a viewer facing the invention illustrated in  FIGS. 1 and 3 . Referring now to the drawing for a better understanding of this invention, and more particularly to the embodiment shown in  FIGS. 1-3 , a surge relief valve assembly  14  is illustrated in a pressure relief system, including a pipeline, vessel, or tank having an inlet generally indicated at  10  with a flange  12  thereon. The surge relief valve assembly has a lower flange  16  connected to upper system flange  12  by suitable bolt and nut combinations shown at  18 . The main body  20  of the assembly has an inlet  22  and outlet  24 . A threaded port normally used with other applications of this main valve body generally contains plug  118 F. Outlet  24  has a flange  26  that can be connected to an outlet flange  28  and pipe  30  in a similar fashion as inlet flange  16 . Fluids flow through the valve from inlet area  51  to outlet areas  52  and  54  once the piston  60  is forced by pressure in an upward direction away from nozzle surface  64 . Areas  52  and  54  are contiguous, with  52  having a generally annular shape around the circumference of piston  60  and liner  58 .  
         [0017]     Although the claims of the present invention are not intended to be limited to any certain dimensions, in a preferred embodiment, the flanged valve sizes can be 1×2; 1½×3; 2×3; 3×4; 4×6; 6×8; 8×10; or 12×16 (all dimensions in inches), for example. In addition to these nominal sizes, the flanged inlet connection  16 ,  12 , and  18 , and flanged outlet  26  can be replaced by American National Standard Taper Pipe Threads (NPT) by using a main valve body  20  with an alternate machining configuration at inlet  22  and outlet  24 . Such NPT connections do not require bolting  18 , but rather screw together tightly with the use of wrenches, and are made leak-tight through the use of an appropriate sealing compound applied to the threads.  
         [0018]     At the top of main valve body  20 , bolts  34  having an appropriate material specification for pressure-containing service, secure cap  32 . The tightened cap holds cylindrical liner  58  in position within the matching bore  56  that is machined into body  20 . Elastomeric O-rings  309  provide leak-tight seals between the interfacing metallic surfaces of body  20 , liner  58 , and cap  32 . Within the bore of liner  58  lies piston  60 , which slides freely up and down between nozzle surface  64  and the underside of cap  32 . To prevent metal-to-metal contact and possible scoring between piston  60  and liner  58 , wedge ring  312  and wear ring  313  are fit into shallow grooves in the piston that allow the outboard surface of each ring, and not the outside surface of the piston, to slide against the liner bore as the piston moves up and down. Items  312  and  313  are made of graphite-filled PTFE (polytetrafluoroethylene).  
         [0019]     Attached to the top of cap  32 , generally by a suitable welding process, is dome reservoir  301 . This dome reservoir provides a dome volume  70 X that is supplemental to dome region  70  contained within the main valve body and cap envelope. The internal volume of reservoir  301  will vary depending on the nominal size of assembly  14 . Fluid transfer between dome volumes  70  and  70 X is made possible by port  302  in main valve cap  32 . Parts of dome reservoir  301  are fabricated from piping components or other suitable parts of a sufficient thickness to withstand the design pressure of the reservoir. Parts of the reservoir assembly are generally assembled using an appropriate welding process, with typical final welds shown as  301 A.  
         [0020]     Piston seal  310 , an elastomeric O-ring, provides the pressure- and leak-tight seal between piston  60  and liner  58 . A PTFE back-up ring  311  is designed to give the O-ring support and prevent excessive deflection of the O-ring into the gap between metal parts  58  and  60 .  
         [0021]     In addition to its sliding surface contact with the bore of liner  58 , wedge ring  312  also provides a dampening function to help ensure smooth piston movement. As pressurized fluid in dome region  70  exerts a downward force on piston seal  310  and back-up ring  311 , items  310  and  311  in turn exert this downward force on wedge ring  312 . The generally triangular cross-section of the wedge ring and its matching recess within piston  60  causes an increased frictional force of the ring against the bore of liner  58  during piston travel. This increased friction induces drag on the movement of the piston and reduces the likelihood of rapid piston movements or oscillations.  
         [0022]     At the bottom of piston  60  as shown, the main elastomeric O-ring seat  62  is secured in place by retaining plate  61 . The latter plate is held in place by bolt  61 A, which is tightened into a threaded hole in the piston. A locking thread insert  61 B within the threaded hole in piston  60  provides resistance to vibration and loosening torque in order to keep bolt  61 A secure and tight. Leak-tight closure of piston  60  is provided by the interference fit (squeeze) between seat  62  and metallic nozzle surface  64 , the latter having a raised portion to directly impinge on the seat. Nozzle  64  is composed of stainless steel, either through application of a corrosion-resistant weld overlay to the surface of the casting, if the casting is made of carbon steel, or by virtue of it having been machined directly into the casting material if a stainless steel casting is used.  
         [0023]     Main valve body  20  has an outer planar mounting face  76  through which dome port  72  extends. Port  74  may also exist in the body, if machining has already been performed to prepare body  20  for use in a pilot-operated pressure relief valve application. If this is the case, plug weld  74 A will be added by an appropriate manual welding process to render port  74  inoperative. In order to allow the appropriate fluid to be routed into dome region  70  from dome port  72 , the top of liner  58  is machined with an annular space  66  and series of small radial ports  68 .  
         [0024]     The outer portion of dome port  72 , on the left in  FIG. 3  as shown, is machined with an appropriate thread, such as NPT, to allow connection of an appropriate dome gas supply, control components, and fittings. A typical dome gas supply configuration is shown in  FIGS. 1, 2 , and  3  as follows: precision gas regulator  321 , manual valves  322 , pressure gage  323 , threaded cross  324 , male hex nipple  325 , tubing  326 , roughing regulator  327 , manual block valve  328 , and gas storage cylinder  329 . Gas regulator  321  may be located by the end user of the surge relief assembly according to their configuration of gas supply tanks or other gas source. Gas supply will generally be provided by the end user.  
         [0025]     In some aspects (not shown), reservoir  301  is separate from cap  32 . In these aspects, port  302  is configured to accept one end of a piping arrangement and reservoir  301  is provided with a port to accept the other end of the piping arrangement and the piping arrangement provides fluid communication between volumes  70  and  70 X. The piping arrangement can be of any type known in the art, as configured for the parameters of the pressure relief system.  
       Operation  
       [0026]     A set, or trigger, pressure is specified by the user of the surge relief valve assembly according to the operational parameters of their pipeline system, vessel, or tank. The value chosen corresponds to the point at which excess system pressure must be relieved, and is frequently the maximum allowable working pressure as defined by the governing piping or vessel design code.  
         [0027]      FIG. 4  shows the surge relief valve assembly of  FIG. 3  in a closed position.  FIG. 5  shows the surge relief valve assembly of  FIG. 3  in an open position. The set pressure of the surge relief valve assembly is set and maintained by charging dome volumes  70  and  70 X with a predetermined pressure of a gas such as nitrogen or air. With the main valve closed, as shown in  FIG. 4 , the dome gas is trapped within a fixed leak-tight volume. At all times, dome gas is completely separate and independent from the process fluid present at the valve inlet  51 . Depending on the specific operating environment, temperature compensation may be necessary to maintain constant dome pressure, as pressures of fixed gas volumes rise with increasing temperature and fall with decreasing temperatures. In some aspects, a self-relieving type of regulator  321  is used for temperature compensation. Regulator  321  bleeds off any pressure increase that develops in dome regions  70  and  70 X due to increased ambient temperature. In some aspects, temperature compensation involves the use of a buried tank or plenum which, by virtue of its isolation underground, will not be susceptible to internal pressure increases as a result of ambient temperature variations.  
         [0028]     The value of dome gas pressure that corresponds to a specified set pressure is a function of the ratio of main valve seat or nozzle area to piston seal area for the valve size in question. Each surge relief valve size has a characteristic area ratio, which can be calculated directly from the machining dimensions of nozzle  64  and liner  58 . For example, in a 3″ by 4″ main valve with a nozzle diameter of 3.05 inches and liner inside diameter of 3.50 inches, the seat-to-seal area ratio equals 0.76; for a specified valve set pressure of 500 pounds per square inch (psi), the corresponding dome gas pressure would equal (0.76)×(500) or 380 psi. Establishment of correct dome pressure will, as set pressure is reached, result in zero net force acting on the piston when considering the dome gas acting downward on the piston and system fluid acting in an upward direction.  
         [0029]     In  FIG. 4 , the force generated by the dome gas, hereafter referred to as the dome force, on piston  60  is greater than the force generated by the process fluid, hereafter referred to as the process force, on retaining plate  61 . For example, the dome force is proportional to the pressure of the process fluid on retaining plate  61  and the area of retaining plate  61 . Thus, piston  60  is pushed downward, toward inlet  51  and seat  62  seals against nozzle  64 . As the process fluid pressure reaches and then slightly exceeds the set pressure, the piston  60  is moved in an upward direction, away from said inlet, moving seat  62  off of nozzle  64 , as shown in  FIG. 5 . As seat  62  moves, the process fluid begins to flow up through inlet passage  51  to outlet  54 , reducing the pressure of the process fluid and relieving excess system pressure. Piston travel is allowed to begin essentially instantaneously, dependent solely on the balance of the forces exerted by the dome gas and the process fluid on the piston at any instant. That is, piston travel, and hence fluid communication, or fluid flow, between the inlet passage  51  and outlet passage  54 , is responsive to the differential between the dome force and the process force. The fluid communication between the inlet passage  51  and outlet passage  54  is proportional to the differential between the dome force and the process force and can change incrementally in response to incremental changes in the force differential.  
         [0030]     As shown in  FIG. 5 , piston  60  continues its travel upward as the force generated by the process fluid on retaining plate  61  continues to rise. As piston  60  moves upward, the volume encompassed by regions  70  and  70 X decreases. Consequently, the dome gas is compressed to a higher pressure. The internal volume for dome reservoir  301  is selected so that the allowable rise in dome gas pressure from a closed main piston  60  ( FIG. 4 ) to fully open piston ( FIG. 5 ) is generally 5 to 7%, but may vary depending on specific applications. The selection of the internal volume for dome reservoir  301  is determined through a combination of calculations to determine inlet  51  size required for process fluid flow and actual test data on prototype valve assemblies.  
         [0031]     As the process force abates, the compressed dome gas forces piston  60  downward. When the dome force is equal to the process force, piston  60  closes and seat  62  seals tightly against nozzle  64 .  
         [0032]     Thus, it is seen that the objects of the invention are efficiently obtained. While a preferred embodiment of the present invention has been illustrated in detail, modifications and adaptations of the preferred embodiment may be readily apparent to those having ordinary skill in the art. It is to be understood that such modifications and adaptations are considered to be within the scope and spirit of the present invention as set forth in the following claims.