Abstract:
A valve has a housing including a valve seat. A valve pin is supported by a housing through a support shell. The support shell and the valve pin have distinct coefficients of thermal expansion such that when exposed to a temperature change, movement of the support shell moves differently than the pin. In this way, the valve pin can be caused to move toward and away from the valve seat to allow operation of the valve.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a valve that provides precise movement of a valve pin relative to a valve seat through the use of materials having distinct coefficients of thermal expansion. 
         [0002]    Valves are utilized in any number of applications to control the flow of fluids from one location to another. In a typical valve, a valve seat receives a valve pin, and when the valve pin is seated in the seat, fluid flow is blocked from an upstream location to a downstream location. The valve pin is moved relative to the valve seat to allow fluid flow. 
         [0003]    Typically, some actuator is provided to move the valve pin. The use of an actuator requires additional components, and is somewhat expensive. Moreover, the actuator may not provide precise movement, or adequate sealing. 
         [0004]    It has been proposed to utilize a material which expands or contracts with heating and cooling to form the valve pin. In such valves, the valve pin moves when heated to allow flow of fluid. 
       SUMMARY OF THE INVENTION 
       [0005]    A valve has a housing including a valve seat. A valve pin is supported by a support shell. The support shell and the valve pin have distinct coefficients of thermal expansion such that when exposed to a temperature change, the support shell moves differently than the valve pin. In this way, the valve pin can be caused to move toward and away from the valve seat to allow operation of the valve. 
         [0006]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1A  shows first embodiment. 
           [0008]      FIG. 1B  shows the first embodiment valve seated. 
           [0009]      FIG. 2  shows a second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]    A valve  20  is shown in  FIG. 1A  having a valve pin  22 . Valve pin  22  has a head  24  that selectively seats in a valve seat  26  to control the flow of a fluid from an upstream location  35 , to a port  36 , through the valve seat  26 , and to a downstream port  38  in a downstream connection  40 . 
         [0011]    The valve pin  22  is coupled at  28  to a support shell  30 . The support shell  30  is received within a bore  31 , and coupled at  32  to the housing  34 . The coupling at  28  and  32  may be performed by welding or other techniques known in the art. The support shell  30  is formed of a material having a different coefficient of thermal expansion than the valve pin  22 . The difference in the coefficient of thermal expansion may be selected such that the coefficient of one of the materials will be at least twice the coefficient of the other. This will provide significant movement that can be achieved in a relatively short period of time to provide better control over the amount of a sample fluid, as an example. 
         [0012]    In one embodiment, the support shell  30  and the housing  34  are formed of a stainless steel, and in particular stainless steel 304. In that same embodiment, the valve pin  22  may be formed of a tungsten. With such materials, the stainless steel will expand with a coefficient of thermal expansion that is three or four times the coefficient of the tungsten. 
         [0013]    While the support shell  30  is shown in  FIG. 1A  as a cylindrical element surrounding a cylindrical valve pin, other embodiments of the support shell  30  which support the valve pin  22  for movement relative to the valve seat  26  can be utilized. As an example, spaced legs, or even a single support leg may support the valve pin  22  and cause movement of the valve pin  22  relative to the valve seat  26 . 
         [0014]    When exposed to heat, the support shell  30  will expand more than the valve pin  22 . Since the two are connected together, this will cause the valve pin  22  to move to the left as shown in  FIG. 1A , and such that the head  24  moves from the position shown in  FIG. 1B  at which it seals the connection, to the position shown at  FIG. 1A , wherein it allows fluid flow. A heater  42  may be provided to drive the expansion. Alternatively, the valve  20  may be responsive to environmental heat to provide this movement. 
         [0015]    The present invention is capable of providing very precise movement of the valve pin  22 , such that extremely small amounts of fluid can be metered between port  36  to port  38 . The valve  20  is particularly well suited for applications in which it is desirable to gather a small metered quantity of a gas. 
         [0016]    While the valve pin  22  is described as having the lower coefficient of thermal expansion relative to the support shell  30  or housing  34 , the opposite could be utilized. In addition, while heating is disclosed as actuating the valve  20 , in fact cooling can be used to actuate the valve  20  in other embodiments. For example, depending upon the materials selected for the valve pin  22  and the support shell  30 , the valve  20  can be configured to passively open or close responsive to an increase or decrease temperature. 
         [0017]      FIG. 2  shows another embodiment of a valve  51  wherein a valve pin  43  is received within a support shell  44 , and a heater coil  46  is provided. The valve pin  43  has a head  48  selectively received in an opening  54  in a diaphragm  50 , where the diaphragm  50  at opening  54  serves as a valve seat for valve pin  43 . Diaphragm  50  is secured within a housing  52 . An inlet  56  extends into a chamber  57 , and an outlet  58  extends outwardly of the chamber. A vacuum connection  62  is applied to an opposed side of the diaphragm. 
         [0018]    In the embodiment shown in  FIG. 2 , the materials and basic mounting of the support shell  44  and valve pin  43  may be as shown for the support shell  30  and valve pin  22  of the  FIG. 1A  embodiment. As shown in  FIG. 2 , the support shell  44  is supported within the housing  52 . A weld joint  100  secures the diaphragm  50  within the housing  52 . 
         [0019]    A frit  70 , which may be formed of a powdered sintered metal, allows a controlled amount of leakage across its surface area in a pre-determined period of time. In this embodiment, a very precise amount of gas may be sampled by simply actuating the valve  51  to pull the valve pin head  48  away from the opening  54 , and while a vacuum is applied. This will sample a very precise amount of the fluid flowing between inlet  56  to outlet  58 . The sample is drawn across the frit  70  and into connection  62 . 
         [0020]    In the embodiments as depicted in  FIGS. 1A and 2 , the valve pins  22  and  43  may be held against the valve seat  26  and opening  54  in diaphragm  50  to provide a very tight fit, and a very secure seal to prevent leakage. The diaphragm  50  also allows the embodiment to be utilized in extremely cold environments. In such a cold environment, thermal expansion will operate to cause the sleeve and pin to be drawn toward the diaphragm to provide a very tight fit. The flexible diaphragm allows this movement, without damage to the overall valve. In prior art valves having moving valve parts, to provide a solid or high force holding the valve pin against the seat requires that same high force to be overcome. However, since the expansion of the materials in the disclosed embodiments is what causes the movement here, that concern does not apply as much as in the prior art. Also, very precise movement of a valve element relative to its housing is provided by the disclosed embodiments, and precise metering can be achieved. 
         [0021]    In one application, an embodiment of the valve  20  of  FIG. 1A  was made to close off a fused silica capillary with an internal dimension of 100 micrometers (0.0039 inches). With a two inch (50.8 mm) tungsten pin and 200 degree F. (93.33 degrees C.) rise in temperature, the gap between the valve pin  22  and the valve seat  26  is 0.0029 inches (73.66 mm). This gap is well suited for this 100 micrometers capillary application. The diameter of valve pin  22  and the wall thickness of the support shell  30  may be selected such that the valve seat  26  can be operated within the elastic limits of the material and hold helium leak rate of less than 10**−10 standard cubic centimeter per second (SCCS). A worker of ordinary skill in the art, armed with the coefficients of expansion, and the particular sizes of the components, would be able to calculate the relative movement of the valve pin  22 , and the support shell  30  to achieve this tight control. 
         [0022]    In many valve applications, both the valve pin and the valve seat are polished after formation. However, it is preferred in this embodiment that only the valve pin is polished, with the valve seat left unpolished. Then, during initial run-in, the valve will form the actual contour of the valve seat such that a very tight and precise seat will be provided that will block almost all leakage. 
         [0023]    The valves  20  and  51  of  FIGS. 1A and 2  have no moving parts, making the valves  20  and  51  very reliable and simple to manufacture. Dead volume is very small, which is well suited for applications requiring low leak rate, low dead volume and reliable applications such as gas chromatography, flow switching devices, and vacuum systems. Of course, any other size and material may be used. 
         [0024]    Although embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.