Abstract:
A relief valve having blow down values of 5% or lower is disclosed. The low blow down values are the result of reducing friction within the relief valve. The relief valve includes a movable plunger. Clearance is provided whereby the plunger does not experience significant friction as it moves into sealing contact with the seal assembly. An energized seal assembly forms a tight seal against the plunger while creating little friction, as the seal is elastomeric and the point of contact is minimized. The relief valve further includes an outlet port, which is adjustable 360° about the relief valve.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pressure relief valve and more particularly to a pressure relief valve having a reduced blow down pressure of about 5% or less and further having an outlet port which is adjustable 360° about the relief valve. The relief valve also has a pressure energized seal. 
     2. Description of the Prior Art 
     Relief valves are placed in piping systems, pressure vessels and other systems to vent excess pressure from the system in an attempt to prevent damage to the system without endangering the workers or environment. In a relief valve, the pressure at which the valve opens, known as the set pressure, is a function of the spring rate and the initial friction of the seals. The pressure at which the valve closes is also dependent on the set pressure and the stick friction of the seals. Typically, the larger the stick friction component, the lower the system pressure must fall to allow the relief valve to close. The amount the pressure must fall below the set point to allow the relief valve to close is called “blow down”. 
     Blow down is typically expressed as a percentage of the set point (also known as set pressure). For example, if the set point is 4,000 psi, and the blow down dead band is 20%, the pressure within the system must fall to approximately 3,200 psi before the relief valve will close and reseat. High blow down in this type of relief valve is undesirable. 
     Prior art relief valves typically have a blow down of approximately 15-30%. For example, if the set pressure is 4,000 psi, the pressure must drop to 2800 to 3400 psi before the opened valve reseats. The 1200-600 psi pressure drop represents 30-15% of the set pressure. 
     Various types of relief valves are known in the art such as those disclosed in the following U.S. Pat. Nos.: 5,168,895; 4,790,348; 4,530,373; 4,313,463; 4,284,101 and 3,232,314. Copies of these patents are included in the Information Disclosure Statement filed concurrently herewith. 
     A commercially successful relief valve is the subject of U.S. Pat. No. 4,456,028 issued in 1984 and assigned to Gilmore Valve Co., the assignee of the present invention. In order for this relief valve to close, a metal seal disk must slide across a metal sealing surface into sealing engagement with the valve outlet bore. This metal to metal sealing assembly causes friction, resulting in a blow down of approximately 20%. It would be desirable from a systems standpoint to reduce the blow down of the relief valve. 
     Prior art relief valves further typically include a predetermined outlet port position. At best, the position of the prior art outlets could be changed by disassembly and reconstruction of the valve. A relief valve having an outlet port that is easily and variably positioned without disassembling the valve is desirable. Such a valve is user friendly and easy to install. The present invention has an outlet port that is adjustable 360° about the relief valve. 
     SUMMARY OF THE INVENTION 
     A relief valve is disclosed that performs with blow down values of about 5% or less. This is accomplished by reducing the friction experienced by the relief valve during closing. The relief valve includes a body which houses a plunger that comes into sealing contact with the valve inlet. Clearance is provided between the body and the plunger, thereby eliminating friction on the plunger as it moves into sealing contact with the seal assembly. An energized seal assembly forms a tight seal against the plunger while creating little friction. 
     The relief valve further includes an outlet port, which is adjustable 360° about the valve. An adapter block that defines the relief valve outlet port includes an annular portion that surrounds and is freely rotatable about the valve and a projecting portion that defines the valve outlet port. The adapter block rotates upon o-rings that create a seal as well as providing a sliding surface for the adapter block. The adjustable position outlet port greatly improves the ease of installation of the relief valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the low blow down relief valve of the present invention. 
     FIG. 2 is a cross sectional view of the low blow down relief valve of FIG. 1 with the valve in the closed position. 
     FIG. 3 is a cross sectional view of the low blow down relief valve of FIG. 1 with the valve in the open position. FIG. 4 is an enlarged cross sectional view of the seal assembly of FIG.  2 . The seal assembly is shown in the valve closed position of FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, a pressure relief valve is generally designated  10 . The relief valve  10  includes a valve bonnet  14 , an adjusting screw  16 , a locking nut  18  to secure adjusting screw  16  in place, an adapter block  20  and a valve cap  22 . The interrelation of these components is illustrated more clearly in the cross sectional view of FIG.  2 . 
     As seen in FIG. 2, the relief valve  10  includes a body  12  having a central bore  24 . The body  12  includes at least one transverse bore  26 , and an annular channel  28  that are in fluid communication with the central bore  24 . 
     The central bore  24  houses a plunger  30  that moves axially within the central bore  24  of body  12 . The plunger includes a first reduced diameter portion  32  defining a first plunger shoulder  34 , and a second reduced diameter portion  36  defining a second plunger shoulder  38 . The plunger  30  and the central bore  24  are sized so as to create a clearance between the plunger  30  and body  24 , thereby eliminating friction between the plunger  30  and central bore  24  when the plunger  30  moves within the central bore  24 . 
     The valve bonnet  14  has a central bore  40 , and at least one transverse bore  42 . Transverse bore  42  is in fluid communication with the transverse bore  26  and annular channel  28  of body  12 . The bonnet  14  houses body  12  and plunger  30  within bonnet central bore  40 . The bonnet further houses a compression spring  44  that engages the first plunger shoulder  34  through a spring disk  46 . 
     Those skilled in the art will recognize that in order to achieve different set pressure ranges for the relief valve  10 , springs with different degrees of flexibility, typically expressed as spring rate in pounds per inch, may be used. The following set pressures/spring rates are for a ½ inch relief valve  10 . These examples are given for illustrative purposes only and are not meant to be limiting in any way. 
     
       
         
               
               
             
               
               
               
               
             
           
               
                   
               
               
                 Set Pressure 
                 Spring Rate 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 150-500 
                 psi 
                 60 
                 lb./in. 
               
               
                 450-2,000 
                 psi 
                 250 
                 lb./in. 
               
               
                 1,800-3,500 
                 psi 
                 400 
                 lb./in. 
               
               
                 3,500-5,500 
                 psi 
                 950 
                 lb./in. 
               
               
                 5,000-6,000 
                 psi 
                 2,000 
                 lb./in. 
               
               
                   
               
             
          
         
       
     
     At higher-pressure ranges, it may be necessary to use a first spring  44  and a second spring, not shown. The springs are nested one inside the other. However, for lower pressure ranges, a single spring  44  will suffice. 
     The spring  44  is captured between an adjusting screw  16  and the spring disk  46  through a washer  48 . The adjusting screw  16  threadably engages the valve bonnet  14 . Rotation of the adjusting screw  16  compresses or relaxes the tension in the spring  44 , thereby increasing or decreasing the set point of the relief valve  10 . The adjusting screw  16  is held in place by tightening lock nut  18  against bonnet  14 . 
     The exterior surface  50  of bonnet  14  includes a reduced diameter segment  52  sized to accept the adjusting block  20 . The reduced diameter segment  52  includes o-ring channels  54  housing o-rings  56 . The adjusting block  20  includes an annular portion  58  which surrounds the reduced diameter segment  52  of bonnet  14 , and is freely rotatable upon o-rings  56 . The o-rings  56  also create a seal between the adjusting block  20  annular portion  58  and the bonnet  14 . 
     The adjusting block  20  further includes a projecting portion  60  that defines valve outlet port  62 . The rotation of the annular portion  58  about the bonnet  14  determines the location of the outlet port  62  relative the relief valve  10 . The valve outlet port  62  is preferably threaded to facilitate connection to downstream piping. 
     The adjusting block annular portion  58  and the bonnet  14  form a channel  64  that is in fluid communication with the bonnet transverse bore  42 , the body annular channel  28 , the body transverse bore  26 , the body central bore  24  and the outlet port  62 . 
     When in the valve closed position, the plunger second shoulder  38  is engaged by a retainer  66  that limits the movement of the plunger  30  within the central bore  24 . The adjusting block  20 , body  12 , plunger  30  and spring  44  are secured in place by the valve cap  22 . The valve cap  22  includes threads  72  that engage the bonnet  14  at bonnet threads  70 . 
     The valve cap  22  defines the inlet port  74  that may be threaded to facilitate connection to exterior piping and a pressurized fluid source, not shown. The valve cap  22  further includes a sealing assembly generally designated  68 . 
     Relief valve  10  is shown in the closed position in FIG.  2 . The spring  44  urges a sealing surface  80  of the second reduced diameter portion  36  of plunger  30  into sealing contact with the seal assembly  68  of the valve cap  22 . The seal assembly  68  creates a seal between the plunger  30  and the inlet port  74  to prevent fluid from flowing from the inlet port  74  to the outlet port  62 . 
     FIG. 3 illustrates the relief valve in the open position. When the pressure from the pressurized fluid source (not shown) exceeds the set point of the spring  44 , the pressure exerts a lifting force on the plunger  30  to compress the spring  44 . As the plunger  30  disengages the seal assembly  68 , fluid flows from the inlet port  74  to the outlet port  62  through the body central bore  24 , the body transverse bore  26 , the body annular channel  26 , the body transverse bore  42  and the channel  64 . 
     As the pressure dissipates below the spring set point, the spring  44  urges the plunger  30  towards the inlet port  74 . Due to the clearance between the body  12  and the plunger  30 , the plunger  30  does not experience significant friction as it moves into the valve closed position of FIG.  2 . The only friction experienced is as the plunger  30  sealing surface  80  just touches or ‘kisses’ the seal assembly  68 . The use of an elastomeric seal, as opposed to the metal to metal seal of the prior art, as well as the minimization of the sealing contact reduces the friction created during valve reseat and closing. This reduction in friction reduces the blow down, resulting in blow down values of 5% or lower. 
     The seal assembly  68 , also known as an energized seal, is seen in more detail in FIG.  4 . The retainer  66  includes a lip projection  76  that in combination with a lip projection  78  of the valve cap  22  creates a seal assembly cavity  82  between the retainer  66  and the valve cap  22 . Housed in the seal assembly cavity  82  are a wedge shaped seal  84  and an o-ring  86 . The wedge shaped seal  84  needs to be relatively stiff and can be formed from Delrin® or other suitable materials. The o-ring  86  can be formed from typical elastomers such as bung-N. The o-ring  86  must be capable of being deformed under operational pressure. The seals  84 , 86  are held in position within the assembly cavity  82  by the protruding lips  76 , 78 . As the sealing surface  80  of the plunger  30  comes into contact with the wedge seal  84 , pressure exerted on the o-ring  86  squeezes the o-ring  86  causing it to exert lateral force against the wedge shaped seal  84 . This forces the wedge seal  84  toward the plunger sealing surface  80  creating a tight seal with minimum friction causing contact. The seal assembly  68  is sometimes referred to as an “energized seal” in the industry. 
     Having described the invention in detail, those skilled in the art will appreciate that modifications may be made of the invention without departing from its spirit. Therefore, it is not intended that the scope of the invention be limited to the specific embodiment illustrated and described. Rather, it is intended that the scope of this invention be determined by the appended claims and their equivalents.