Abstract:
A poppet element of a valve is provided. The poppet element is movable relative to a valve seat of the valve and includes a balance chamber wall defining a balance chamber with a center body partially fixed relative to the valve seat, an upper head, a balance chamber holder having a coefficient of thermal expansion (CTE) that is matched with that of the upper head and a fastening element disposed to fasten the balance chamber holder to the upper head. The balance chamber holder is disposed between the center body and the balance chamber wall and configured to prevent thermal loading transfer from the balance chamber wall to the fastening element.

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a balance chamber defined by a poppet element of a valve and, more particularly, to a balance chamber defined by a poppet element of a high temperature valve. 
     Steam turbine control and stop valves often employ a balance chamber. During valve opening incidences, steam inside the balance chamber is evacuated through equalizer valves or poppet valves so that pressure inside the balance chamber is reduced and lesser hydraulic force is required to open the valve. 
     In order to ensure that a pressure inside the balance chamber is minimized, clearances between a valve disk and a wall of the balance chamber are often reduced as much as possible with seal rings used to provide high quality sealing characteristics. However, clearance reduction is limited since some predefined amount of clearance needs to be maintained in order to ensure that the valve opens and closes without jamming. 
     In certain applications, a balance chamber may be fixed to an upper head via bolts and, in some cases, the balance chamber material is different from the upper head material. The different materials have correspondingly different coefficients of thermal expansion (CTE) and, as such the upper head and the balance chamber expand at different rates when heat is generated (i.e., when the steam turbine starts up). At steady state, due to the difference in the CTEs, a bending stress is placed on the bolts and this bending stress is transmitted to the upper head via shear stress. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a poppet element of a valve is provided. The poppet element is movable relative to a valve seat of the valve and includes a balance chamber wall defining a balance chamber with a center body partially fixed relative to the valve seat, an upper head, a balance chamber holder having a coefficient of thermal expansion (CTE) that is matched with that of the upper head and a fastening element disposed to fasten the balance chamber holder to the upper head. The balance chamber holder is disposed between the center body and the balance chamber wall and configured to prevent thermal loading transfer from the balance chamber wall to the fastening element. 
     According to another aspect of the invention, a power plant valve including a poppet element movable relative to a valve seat is provided. The poppet element includes a balance chamber wall defining a balance chamber with a center body partially fixed relative to the valve seat, an upper head, a balance chamber holder having a coefficient of thermal expansion (CTE) that is matched with that of the upper head and a fastening element disposed to fasten the balance chamber holder to the upper head. The balance chamber holder is disposed between the center body and the balance chamber wall and configured to prevent thermal loading transfer from the balance chamber wall to the fastening element. 
     According to yet another aspect of the invention, a power plant is provided. The power plant includes a boiler element, a steam turbine, piping disposed to transport steam from the boiler element and toward the steam turbine and a valve disposed along the piping. The valve includes a valve seat and a poppet element, which is movable relative to the valve seat to open or close the valve. The poppet element includes a balance chamber wall defining a balance chamber with a center body partially fixed relative to the valve seat, an upper head, a balance chamber holder having a coefficient of thermal expansion (CTE) that is matched with that of the upper head and a fastening element disposed to fasten the balance chamber holder to the upper head. The balance chamber holder is disposed between the center body and the balance chamber wall and configured to prevent thermal loading transfer from the balance chamber wall to the fastening element. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of a portion of a steam turbine; and 
         FIG. 2  a side schematic view of a balance chamber for use with the steam turbine of  FIG. 1  in accordance with embodiments. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     While balance chamber bolts may be subject to bending stress, which may be transmitted to an upper head via shear stress, in a balance chamber of a steam turbine the bending stress can be within acceptable parameters in certain situations. However, as steam turbines are designed for operation within high temperature regimes, the bending stress may exceed the acceptable parameters by such a degree that material upgrades are insufficient to prevent damage due to differences between the respective coefficients of thermal expansion (CTEs) of the upper head and the balance chamber that may be caused by the use of different materials for the upper head and balance chamber, which is driven by design requirements, manufacturability and costs. 
     Therefore, with reference to  FIGS. 1 and 2 , a balance chamber  10  is provided for use in a power plant  20  or in another similar application. As shown in  FIG. 1 , the power plant  20  includes a boiler element  21  that is formed to define an interior  22  into which heated fluid is directed. This heated fluid may include, for example, gas turbine exhaust where the boiler element  21  is provided as a heat recovery steam generator disposed downstream from a turbine section of a gas turbine engine. 
     The power plant  20  further includes high pressure (HP) piping  23  disposed in an HP section  210  of the boiler element  21 , intermediate pressure (IP) piping  24  disposed in an IP section  211  of the boiler element  21  and low pressure (LP) piping  25  disposed in an LP section  212  of the boiler element  21 . The HP piping  23 , the IP piping  24  and the LP piping  25  extend through the interior  22  and carry fluid that is heated by the heated fluid to produce steam. This steam is then transported by the HP piping  23 , the IP piping  24  and the LP piping  25  toward a steam turbine  26  where the thermal energy of the steam is converted into mechanical energy that can be used to generate power or electricity. 
     The balance chamber  10  may be provided as a component of a combined valve  30  that is operably disposed between the IP piping  24  and the steam turbine  26 . In accordance with embodiments, a valve similar to the combined valve  30  (known as a Main Stop and control valve) may also be operably disposed between the HP piping  23  and the steam turbine  26 . 
     As shown in  FIG. 2 , the combined valve  30  includes an inlet pipe  31 , which may be fluidly coupled to the HP piping  23  or the IP piping  24 , an outlet pipe  32 , which may be fluidly coupled to an HP or IP section of the steam turbine  26  and a valve assembly  33  interposed between the inlet pipe  31  and the outlet pipe  32 . The valve assembly  33  includes a valve seat  34 , a center body  35  and a poppet element  36  that is movable (in the direction of arrows X-X) along the center body  35  relative to the valve seat  34  to occupy and move between first and second positions. At the first position (not shown for ease of illustration), the poppet element  36  is displaced from the valve seat  34  and fluid flow is permitted to proceed from the inlet pipe  31  to the outlet pipe  32 . At the second position (as illustrated in  FIG. 2 ), the poppet element  36  contacts the valve seat  34  and fluid flow from the inlet pipe  31  to the outlet pipe  32  is prevented. 
     The center body  35  includes a main member  352 , which may be referred to as an upperhead bushing, and which is fixed in position relative to valve seat  34  and a movable member  351 , which may be referred to as a valve stern, and which is movable with the poppet element  36  such that the center body  35  as a whole is partially fixed relative to the valve seat  34 . The main member  352  includes a tubular member  353  and an inner flange  354  that extends radially outwardly from the tubular member  353 . The poppet element  36  includes an upper head  361 , a balance chamber wall  362 , a valve disk  363  and a balance chamber holder  364 . The balance chamber wall  362  may be an annular-shaped member disposed about the center body  35  to define an annulus  37  within the balance chamber  10 . An upper portion of the valve disk  363  has a clearance fit with the balance chamber wall  362  through a fastening member  38  and a seal element  39 . The clearance is provided so that the valve disk  363  can be moved open or closed relatively smoothly within the balance chamber wall  362 . A lower portion of the valve disk  363  is shaped to register with the valve seat  34  when the poppet element  36  occupies the second position (as illustrated in  FIG. 2 ). 
     An upper portion of the balance chamber wall  362  includes an outer flange  365  that extends radially inwardly from the balance chamber wall  362 . In accordance with embodiments, the inner flange  354  includes an axial facing surface  40  and a radial facing surface  41  and the outer flange  365  includes an axial facing surface  42  and a radial facing surface  43 . The axial facing surfaces  40  and  42  may be substantially co-planar while the radial facing surfaces  41  and  43  may be substantially parallel with one another. The outer flange  365  may also include an axial protrusion  366  that protrudes axially beyond a plane of an axial face of the balance chamber wall  362 . The inner flange  354  may extend axially beyond the axial protrusion  366 . 
     The balance chamber holder  364  is affixed to the upper head  361  by a fastening element  50  and includes a lower portion  60  and an upper portion  61 . The lower portion  60  and the upper portion  61  may be formed integrally with one another or, in accordance with alternative embodiments, may be formed as separate parts that are fastened together by the fastening element  50 . The fastening element  50  may be torqued to a designed pre-stress and include a threaded bolt and a head portion that extends through the balance chamber holder  364  to register with threading provided in or on the upper head  361 . The head portion interferes with a lower surface of the balance chamber holder  364  such that rotation of the fastening element  50  about a longitudinal axis thereof draws the head portion and the balance chamber holder  364  toward the upper head  361  in a tightening direction. In accordance with embodiments, a clearance C will be provided between a lower surface of the upper head  361  and an upper surface of the upper portion  61 . 
     The fastening element  50  may be provided as a plurality of fastening elements  50  and may be arrayed around the center body  35  in an annular-shaped array. 
     The lower portion  60  includes an inner axial facing surface  600  and an outer axial facing surface  601  and the upper portion  61  includes an inner radial facing surface  610  and an outer radial facing surface  611 . The balance chamber holder  364  is disposable such that the lower portion  60  is disposed between corresponding portions of the balance chamber wall  362  and the tubular member  353  and such that the upper portion  61  is disposed between corresponding portions of the outer flange  365  and the inner flange  354 . In this position, the inner axial facing surface  600  may abut and interfere with the axial facing surface  40  of the inner flange  354  and the outer axial facing surface  601  may abut and interfere with the axial facing surface  42  of the outer flange  365 . Similarly, the inner radial facing surface  610  may abut and register with the radial facing surface  41  of the inner flange  354  and the outer radial facing surface  611  may abut and register with the radial facing surface  43  of the outer flange  365 . 
     In accordance with embodiments, the balance chamber holder  364  may be made of a material that has a CTE that is similar to or matched with the CTE of the upper head  361  material. 
     With the configuration described above, the fastening element  50  extends through the upper head  361  and the balance chamber holder  364  and the upper head  361  and the balance chamber holder  364  have similar CTEs such that the upper head  361  and the balance chamber holder  364  thermally expand and contract at similar rates. As such, bending stresses on the fastening element  50  may be limited or reduced while shear stresses on the upper head  361  may be similarly limited or reduced. Also, with the clearance C provided between the lower surface of the upper head  361  and the upper surface of the upper portion  61 , a non-existent or substantially limited contact pressure exists between the upper head  361  and the balance chamber holder  364  during varied operational conditions. This ensures, because of the torques in fastening element  50 , that there is high contact stress between the outer flange  365  and the upper head  361 , and thereby provides for prevention of steam leakage between the balance chamber  10  and the upper head  361 , and thereby provides for prevention of steam leakage between the balance chamber  10  and the upper head  361 . 
     In addition, the lower portion  60  of the balance chamber holder  364  is provided with room to thermally expand and contract during, e.g., startup and shut down operations. That is, during the startup and shut down operations or other varied operational conditions, the lower portion  60  of the balance chamber holder  364  may expand radially outwardly or contract radially inwardly but, in either case, the inner axial facing surface  600  continues to abut and interfere with the axial facing surface  40  of the inner flange  354  while the outer axial facing surface  601  continues to abut and interfere with the axial facing surface  42  of the outer flange  365 . Thus, the thermal expansion and contraction of portions of the balance chamber holder  364  can proceed without transference of thermal loads onto the fastening element  50  or the upper head  361 . 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.