Patent Publication Number: US-2015060718-A1

Title: Valve diffuser for a valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority of European Patent Application No. EP13182117, filed Aug. 29, 2013, the contents of which are incorporated by reference herein. 
     TECHNICAL FIELD 
     The invention relates to a valve diffuser for a valve having a valve seat designed to make contact with a valve body. 
     TECHNICAL BACKGROUND 
     In turbomachines, for example steam turbines, valves are used inter alia for regulating a steam mass flow. For the local supply of power, steam turbines having a comparatively high performance category are required. This has the effect that the valves which are used therefor similarly have a corresponding component size. Valves of this type generally comprise a valve housing and a valve diffuser which is arranged within the valve housing and through which inflowing steam flows. The mass flow of steam is set with the aid of a valve body, which is formed such that it can move in the direction of the valve diffuser. In a completely closed position, the valve cone lies against a sealing surface on a valve seat which is connected to the valve diffuser. In an open position, a through-flow area directly correlated to the mass flow through the valve is formed between the valve cone and the valve seat. 
     In the closed position, the valve cone bears against the valve seat and forms a contact surface. This contact surface is subjected to higher loading owing to the blows of the valve cone upon closing. In addition to wear phenomena arising from instances of steam erosion, this region is therefore also subjected to wear phenomena arising from instances of mechanical loading. In order to counteract such instances of mechanical loading, the contact surface on the valve seat is generally plated, which is effected for example by stelliting. However, despite the plating, after relatively long operation it is often necessary to refurbish the surface of the valve seat on account of solid state erosion and steam erosion. 
     Replacement of the entire valve seat would be one possible way of preventing further damage, but the replacement is made more difficult since assembly work on the turbine is generally associated with increased complexity. 
     It is similarly conceivable to counteract the wear arising from erosion by virtue of an appropriate material selection. Materials of this type are, however, comparatively expensive and damage nevertheless generally arises on the valve seat after a certain operating time. If it is not possible to refurbish a damaged surface of this kind, the valve seat is dismantled and replaced by a new one. In the event of maintenance and during stoppages, the valves are examined and a decision may be made on site as to which measure is required to restore the operation of the valve. Either refurbishment or complete valve replacement is required. Tests such as a dye penetrant test or an ultrasonic test are required for sufficiently good analysis. If a measure is to be taken, there is an appreciable, sometimes extended idle time between when the decision is made and when the measure is taken. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to improve the availability of a valve. 
     This object is achieved by a valve diffuser for a valve having a valve seat designed to make contact with a valve body, wherein the valve seat comprises a bushing for making contact with a valve body. 
     According to the invention, a valve diffuser comprises a bushing which is in contact with the valve body. After specific maintenance intervals defined in advance, this bushing can be replaced irrespective of findings. This saves a large amount of time, since tests are classified as not being necessary from the outset. As a result, the idle times of such a valve are reduced. 
     In an advantageous development, the bushing is formed from a different reinforced material. 
     According to the invention, use is advantageously made of a material for the bushing which has a reinforced form compared to the material of the valve diffuser and is therefore less sensitive to the constant contact with the valve body. Any contact of the valve body on the valve diffuser leads to mechanical deformation and to erosion. It is therefore proposed according to the invention to form this region of the contact surface which is formed by the bushing with a material which is reinforced, compared to the valve diffuser. As a result, the mechanical deformation and the erosion are reduced and the service life of the valve is increased. 
     It is advantageous that the material of the bushing consist of a stellite. In relation to steam states, stellite is a suitable material for counteracting damage. It is advantageous that the bushing has an annular form and that the outer region is formed parallel to the axis of rotational symmetry. The bushing is in this case mounted by being pressed in. In an alternative embodiment, the bushing can have an annular form and the outer region can have a conical form. The outer shape of the bushing therefore has a conical configuration. The greater diameter of the cone is positioned counter to the mounting direction for installing the bushing, and therefore the bushing is fixed in a form-fitting manner. In this respect, the bushing can be mounted, for example, by way of shrink-fitting of the bushing. 
     It is advantageous that complete replacement of the diffuser or of the valve seat is therefore not necessary. Similarly, it is not necessary to remove the complete valve from the turbine. 
     It is a particular advantage that maintenance can be planned better in advance and can be carried out more effectively since the bushing may always be replaced irrespective of findings. 
     As a result, dye penetrant tests and ultrasonic tests can be dispensed with entirely. Complicated and expensive refurbishment which is dangerous to health is not required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be explained in more detail on the basis of an exemplary embodiment. 
       The  FIG. 1  schematically shows a cross section of half of a valve according to the invention. 
         FIG. 2  shows the same section of half of a valve according to the prior art. 
     
    
    
     DESCRIPTION OF AN EMBODIMENT 
       FIG. 1  shows a cross-sectional view of a valve according to the invention. 
     In  FIG. 1 , the valve  1  comprises a valve housing  2  and, within the valve housing  2 , a valve diffuser  3  of substantially rotationally symmetrical design. An axis of symmetry  4  is indicated in the figure. The valve diffuser  3  has a substantially rotationally symmetrical form in relation to this axis of symmetry  4 . The valve diffuser  3  comprises a substantially cylindrical shell region  5 , which is formed substantially parallel to the axis of symmetry  4 . A conical inner shell region  6 , through which steam flows at a comparatively high temperature and high pressure during operation, is formed within the valve diffuser  3 . At the start end  7  or inlet of the valve diffuser, the valve diffuser  3  is fixedly arranged on the housing  2 . 
     The embodiment shown in  FIG. 1  shows the invention above the axis of symmetry  4 . The prior art in  FIG. 2  is shown beneath the axis of symmetry  4 . 
     The valve diffuser  3  comprises a valve seat  8 , which is arranged at the start  7  of the valve diffuser and is designed to make contact with a valve body  14 , shown schematically. The valve body is shaped, controlled and moved conventionally, so details thereof are not illustrated. The valve body touches the valve seat  8  substantially in the contact region  9 . The contact region  9  is improved by a bushing  10 . The bushing  10  now makes the contact with the valve body (not shown in more detail) and is formed from a different reinforced material to the valve diffuser  3 . The material of the bushing  10  preferably consists of a stellite alloy. The bushing  10  has a substantially annular form and is adapted to the valve diffuser inner surface. The outer region  11  of the bushing  10  is formed parallel to the axis of symmetry  4 . 
     In an alternative embodiment, the outer region  11  of the bushing  10  has a conical configuration.  FIG. 1  shows the angle between the axis of symmetry  4  and the conical outer region  11  of the valve bushing, which angle is substantially 0.17°. A range of values for this angle lie between 0.05° and 0.25°. 
     The bushing  10  is pressed in. In the case that the bushing  10  has a conical configuration, the bushing  10  is fixed in a form-fitting manner to the valve diffuser, and the greater diameter of the bushing is arranged counter to a mounting direction  12  of the bushing in the diffuser. The bushing  10  can be mounted by shrink-fitting. 
     In an alternative embodiment, the material of the bushing  10  corresponds to the material of the valve diffuser  3 , and the bushing  10  preferably then has a stellite plating. 
     The prior art in  FIG. 2  has direct contact between the valve body and the diffuser  7  at contact region  9 . There is no bushing, like  10  in  FIG. 1 , protecting the diffuser. The above described benefits of the invention are not achieved. In  FIG. 2 , the elements corresponding to those in  FIG. 1  have the same reference numbers, raised by  20 .