Abstract:
A valve ( 5 ) for relieving fluid pressure comprises a fluid inlet ( 8 ), a fluid outlet ( 9 ) and a piston ( 20 ) in communication with the fluid inlet ( 8 ) and configured to move in response to a fluid pressure at the inlet above a predetermined threshold so as to connect the fluid inlet ( 8 ) with the fluid outlet ( 9 ) and thereby relieve fluid pressure. One or more dampers ( 100; 80 ) are configured to damp the movement of the piston ( 20 ).

Description:
TECHNICAL FIELD 
       [0001]    The embodiments described below relate to a pressure relieving and safety device, particularly a pressure relief valve for use in high pressure application with abrasive or difficult process fluids. 
       BACKGROUND ART 
       [0002]    Worldwide industries as a whole have made huge leaps forward with technology, materials and the systems they employ, that all allow (in particular) the possibility of exploring and operating hydrocarbon producing reserves at higher pressures. To obtain higher production rates and longer life from a field than has been possible before, the drilling systems require higher pressure and flow rates for a number of activities, and thus better protection and safety systems for personnel and equipment. 
         [0003]    There are a number of pressure relieving and safety devices on the market for high-pressure fluid systems where solids and particles above 25 microns are an issue. These items in various combinations can fulfill some of the certification and operational needs of the industries that employ them. For pressure containing systems there is clear legislation on what certification must be provided for a system to achieve the necessary legislative and certification needs, this is particular important when considering pressure containing and hazardous area equipment/installations. 
       DISCLOSURE OF THE INVENTION 
       [0004]    According to a first aspect of the invention, there is provided a valve ( 5 ) for relieving fluid pressure, the valve comprising:
       a fluid inlet ( 8 );   a fluid outlet ( 9 );   a piston ( 20 ) in communication with the fluid inlet ( 8 ) and configured to move in response to a fluid pressure at the inlet above a predetermined threshold so as to connect the fluid inlet ( 8 ) with the fluid outlet ( 9 ) and thereby relieve fluid pressure; and a damper ( 100 ;  80 ) configured to damp the movement of the piston ( 20 ).       
 
         [0008]    A damper reduces the rapid acceleration and deceleration of the valve mechanism and associated stress and wear, thereby substantially reducing the risk of premature failure. 
         [0009]    The piston ( 20 ) may have a stem ( 21 ) connected to a linkage ( 49 ) configured to prevent movement of the piston ( 20 ) until the fluid pressure at the inlet ( 8 ) exceeds the predetermined threshold. 
         [0010]    The valve may comprise a primary damper ( 100 ) comprising a first fluid-containing chamber ( 23 ) defined in part by the piston ( 21 ,  24 ) and in fluid communication with a damping throttle ( 93 ). 
         [0011]    The valve may comprise a body ( 10 , 70 ) having a bore ( 70 ′) in which the piston moves, wherein the first fluid-containing chamber ( 23 ) is defined in part between the outer surface ( 21 ′) of the stem ( 21 ) and the inner surface ( 70 ′) of the bore ( 70 ′). 
         [0012]    The valve may comprise a seal ( 25 ) between stem ( 21 ) and body ( 10 , 70 ) and a fluid port ( 26 ) formed in the body for connection to the damping throttle ( 93 ), the fluid port ( 26 ) lying adjacent the seal ( 25 ). 
         [0013]    The valve may comprise a second fluid-containing chamber ( 91 ) in communication with the damping throttle ( 93 ). 
         [0014]    The second fluid-containing chamber ( 91 ) may be defined by a housing ( 90 ) separate from the body ( 10 , 70 ). 
         [0015]    The damping throttle ( 93 ) may be in the housing ( 90 ). 
         [0016]    The second fluid-containing chamber ( 91 ) may be subject to a bias pressure. 
         [0017]    The housing ( 90 ) may comprise a pressurized gas reservoir ( 92 ) configured to apply a bias pressure to the second fluid-containing chamber. 
         [0018]    The valve may comprise a secondary damper ( 80 ) configured to limit the movement of the linkage ( 49 ). 
         [0019]    The valve may comprise a secondary damper ( 80 ) configured to damp the movement of the piston ( 20 ) after the piston has started to relieve fluid pressure. 
         [0020]    The secondary damper ( 80 ) may comprise an adjustable piston ( 81 ). 
         [0021]    The adjustable piston ( 81 ) may move in a tertiary chamber subject to a bias pressure. 
         [0022]    According to a second aspect of the invention, there is provided a method of operating a valve ( 5 ) for relieving fluid pressure and comprising a fluid inlet ( 8 ), a fluid outlet ( 9 ) and a piston ( 20 ) in communication with the fluid inlet ( 8 ), the method comprising the steps of:
       triggering movement of the piston ( 20 ) in response to a fluid pressure at the inlet ( 8 ) above a predetermined threshold and, thereafter,   damping the movement of the piston ( 20 ).       
 
         [0025]    The second aspect may be particularised by features of the first aspect. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIGS. 1-3  show an embodiment of the present invention in successive stages of operation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    As shown in  FIG. 1 , valve assembly  5  comprises a valve body  10  having a sleeve  70  (having a bore  70 ′) in which is slidingly mounted a piston  20  having a circumferential seal  22 . 
         [0028]    In the rest position shown, the internal piston  20  is in an upper position, and there is a fluid connection between the inlet port  8  and outlet port  9  of the valve body, via a port  30  in the side of the piston and a port  60  formed in a sleeve  70  in the valve body (and shown more clearly in  FIG. 2 ). As shown, the valve is at rest and no parts are under any strain to maintain this position. If any of the parts were to fail during operation, this is the—pressure relieving—state to which the valve would try to return. In other words, it would have “failed in a safe position”. 
         [0029]    The end of the piston stem  21  that lies remote from port  30  is pivotally attached (at  54 ) to a linkage  49  comprising a lower link  51  pivotally attached to an upper link  52  which is in turn connected to a crank  50 . The linkage is contained in a housings  6  and  11  attached to the at split lines  12  and  7  respectively to body  10 , a seal  25  between the sleeve  70  and the circumference of the piston stem  21  preventing flow of fluid from the valve body into the housing. The linkage can be accessed by removal of a cover  6  at separation line  12 . Consequently, there is no need to remove the valve body from the pipework (not shown) connected to the inlet and outlet ports  8 ,  9  whenever routine maintenance or replacement of any of the moving parts is required. Rather, only replacement of the sleeve or valve body would necessitate such a total removal of the valve from the pipework. If necessary, housing  6  and  11 , piston  20  and the seal  25  at the base thereof (discussed in more detail below), can be lifted off the valve body at split line  7  above sleeve  70  while the valve body remains in its normal installation, connected to the pipework. In order to set the valve, and obstruct the open path through the valve body which would otherwise allow pressure relief, the valve load springs (indicated by dashed lines  40 ) must be set up (in accordance with the setting procedure for the operational conditions required and specific to that process). The pressure in the upstream pipework must be minimal, and less than the set pressure of the valve. 
         [0030]    As shown in  FIG. 2 , the internal linkages are now “set” in position, and the piston  20  is at its lowest position vertically. Port  30  is no longer aligned with port  60 , thereby closing the internal passageway that allowed fluid flow through the body of the valve from inlet  8  to outlet  9 . 
         [0031]    The internal linkage is of an over-centre configuration, where the force of the load springs  40  will ensure that the piston  20  cannot be released for vertical movement until the force acting on the piston  20  is overcome by the fluid pressure in the upstream pipe work (not shown). The force acting on the links  51 ,  52  from the piston  20  as a result of the pressure of the fluid at the inlet port  8  acts upon the crank  50 , which is in turn resisted by the load springs  40 . 
         [0032]    When the mechanism is triggered by rotation of the crank  50  sufficient to move—as indicated by arrow R in  FIG. 3 —the upper/lower link pivot point to inline or over centre in the release direction R, the linkage freely articulates to allow the piston  20  to move in a vertical manner as indicated by arrow V, ports  30  and  60  to communicate and a fluid connection between the inlet  8  and outlet  9  to be opened. The pressure acting on the outlet port  60  from “back pressure” in the system has little relation to the release mechanism of the valve, and its ability to trigger/activate. The above features are known per se and consequently not described in any further detail. 
         [0033]    The rapid movement of the piston  20  and the internal linkage  49  as the mechanism operates at its set pressure is extremely quick, and the internal parts have to withstand the rapid acceleration (as the pressure of the fluid in the upstream pipework tries to discharge), and the deceleration in linear velocity of the internal parts as they come to a stop at the end of their travel (in the rest/reset position, with fluid connection between ports  30  and  60  of the valve). 
         [0034]    These rapid movements can mean substantial stress and wear to the internal parts of the valve, and can prevent it from being reset reliably. In accordance with the invention, a primary damping mechanism  100  is employed to substantially reduce the risk of premature failure. 
         [0035]    As illustrated in  FIG. 3 , the damping effect is achieved by transfer of fluid (indicated by solid shading in the figures) from a first chamber  23  to a second chamber  91  located external to, separate and remote from the valve body  10  via a throttle adjustable by knob  93 . 
         [0036]    First chamber  23  is an annular chamber formed between the outer cylindrical surface  21 ′ of the piston stem  21  and the inner bore  70 ′ of the sleeve  70 . Chamber  23  is bounded at its lower end by the upper end surface  24  of piston  20  and at its upper end by the seal  25  between stem  21  and sleeve  70 . A port  26  is provided in the sleeve adjacent the seal  25  for fluid transfer to pipe  101 . 
         [0037]    Second chamber  91  is formed in a housing  90  having a fluid connection  94  to pipe  101 . Fluid flow in and out of the chamber is controlled by a throttle adjustable by a knob  93 . A gas-filled reservoir  92  (separated from the fluid reservoir  91  by a sliding piston  95  and chargeable with a gas via valve  96 ) provides a small amount of biasing back pressure to the fluid in order to allow the damper to reset to its original positions. This pressure is minimal, and is not designed to allow the valve to move back to a “set” position, but simply to move the oil back. 
         [0038]    The outlet flange and connection is rated to the same pressure of the inlet. The limiting factor is the resistance of the piston seals  25  to withstand the backpressure acting upon them, and the piston to withstand external pressure. In the embodiment shown, seals  25  can be made from a variety of materials to suit the process fluid or environmental conditions. 
         [0039]    Accordingly, when the valve mechanism is triggered (“the valve is set off”), piston  20  is initially able to accelerate for the first part of its travel until (only so far as the damping element is absorbing the initial movement) ports  30  and  60  communicate and a fluid connection between the inlet and outlet is opened. Primary damper  100  with compression control decelerates the remaining part of the travel. 
         [0040]    Primary damping mechanism  100  can be tuned to the specific application and controls the fully closed to fully open velocity of the valve mechanism when triggered at its set pressure. The speed of the damping can be adjusted by fine adjustments to the relief ports inside the valve, and/or by changing the viscosity of the damping fluid. These adjustments are done at the testing stage following manufacture, with the provision for fine adjustment on the adjuster screw  93 . Together, this allows the piston to open and relieve pressure as quickly as possible, but decelerates the piston, to prevent damage and potential malfunction. 
         [0041]    As indicated at  80 , a secondary damper is also provided that serves as an end stop, limiting the movement of the linkage  52  so as to prevent over-rotation and damage, as shown in  FIG. 1 . This ensures that the valve cannot jam in the reset position. 
         [0042]    As indicated at  81  in  FIG. 1 , secondary damper has an adjustable piston which assists the primary damping after the piston has started to relieve the pressure in the system, and as such is installed to absorb the kinetic energy that the piston and internal linkages have from their rapid acceleration. As with primary damper  100 , secondary damper  80  also provides a small amount of inherent back pressure by means of an internal, tertiary chamber (not shown) in order to allow it to reset to its original positions. This bias pressure is minimal, and is not designed to allow the valve to move back to a “set” position, but simply to move the oil back. 
         [0043]    In addition to reducing the kinetic energy of the moving parts as they come to a halt, at the end of their travel, secondary damper  80  also ensures the position of the port  30  in the piston is in line with the port  60  in the sleeve  70  of the valve body. 
         [0044]    Although specific embodiments are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the present description, as those skilled in the relevant art will recognize. For example, in the embodiment shown, piston  20  is rated to withstand full pressure and materials can be specified according to the process fluid, and environmental conditions. Thus, the valve as a standard assembly is capable of withstanding up to the inlet pressure as a backpressure on the outlet port, with a calculable degradation of “reset” performance. The teachings provided herein can be applied to other equipment, and not just to the embodiments described above and shown in the accompanying figures. Accordingly, the scope of the embodiments described above should be determined from the following claims.