Abstract:
A valve assembly comprising a housing having an inlet and space therefrom an outlet, means located in the housing for controlling the flow of fluid between the inlet and the outlet, said means including a main valve movable between a first relatively closed position and a second open position, said movement being controlled by a pilot valve assembly including a temperature sensitive member such that when the temperature in the fluid reaches a predetermined value the pilot valve is opened thereby allowing the main valve to move from said first to said second open position.

Description:
[0001]    This application claims priority from British patent application Ser. no. 0027190.8 filed Nov. 7, 2000.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to valve assemblies.  
         OBJECT OF THE INVENTION  
         [0003]    It is an object of the present invention to provide a valve assembly which operates within a fluid cooling system for, for example a vacuum pump to reduce the fluid flow when not required and to open when full flow is needed.  
         SUMMARY OF THE INVENTION  
         [0004]    According to the present invention, a valve assembly comprises a housing having an inlet and spaced therefrom an outlet, means located in the housing for controlling the flow of fluid between the inlet and the outlet, said means including a main valve movable between a first relatively closed position and a second open position, said movement being controlled by a pilot valve assembly including a temperature sensitive member such that when the temperature of the fluid reaches a predetermined value the pilot valve is opened thereby allowing the main valve to move from said first to the second position.  
           [0005]    Preferably, the heat sensitive member is in the form of one or more bimetallic discs which when subjected to a temperature above a predetermined value will cause the pilot valve to open thereby allowing the main valve to move from its first to its second position.  
           [0006]    In one embodiment the main valve has formed therein at least one notch which allows the passage of fluid from the inlet towards the outlet when the main valve is in the first relatively closed position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a cross-sectional view of the valve according to the present invention in its relatively closed position; and  
         [0008]    [0008]FIG. 2 is a cross-sectional view of the valve according to the present invention with the valve in its open position. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]    An embodiment of the invention will now be described, by way of example, reference being made to the Figures of the accompanying diagrammatic drawings.  
         [0010]    Referring to FIGS. 1 and 2, a valve assembly  1  for controlling the temperature of a cooling fluid for use for example with a vacuum pump (not shown) comprises a main housing  2  in which is formed an inlet  4  and space therefrom an outlet  6  for the cooling fluid. Intermediate the inlet  4  and outlet  6  is a chamber  8  formed in the main housing  2 . The chamber  8  is formed on its base  10  with a valve seating  12  which surrounds a through-hole  14  communicating with the outlet  6 . Located in the chamber  8  is a first main valve  16 .  
         [0011]    The main valve  16  is a slide-fit within the chamber  8  and comprises an outer thin-walled body  18  which is a slide fit allowing a controlled leakage of cooling fluid from the inlet  4  up (as shown) between the inner surface of the chamber  8  and the co-operating outer surface of the body  18  towards the upper (as shown) end of the chamber  8 . The base  20  of the body  18  is formed with a through-hole  22  in substantial alignment with the hole  14  and surrounding the hole  22  is a valve surface  24  for engaging the valve seating  12  in the relatively closed position of the valve assembly  1  (see FIG. 1). Formed in the valve surface  24  are notches  26  which permit limited flow of cooling fluid between the inlet  4  and the outlet  6  in the (relatively) closed mode of the valve assembly  1 .  
         [0012]    A member  28  is provided in the body  18  which is spaced from the base  20  and defines therewith a further chamber  30 . The member  28  sits in a recess formed in the inner surface of the body  18  and is maintained in position by an adjustable thread  32  or other means. A through hole  34  is formed in the member  28 , the lower (as shown) circumferential edge of which forms a valve sealing  36  co-operating with a pilot valve assembly  38 .  
         [0013]    The pilot valve assembly  38  is located in the chamber  30  and comprises a member  40  formed with a plurality of spaced holes  41  which is a slide-fit within the chamber  30 . Also formed on the member  40  is a central valve face  42  which co-operates with the valve seating  36 .  
         [0014]    Located beneath (as shown) the member  40  within the chamber  30  is a heat sensitive member in the form of a plurality of bimetallic discs  44  each with a central hole  45 .  
         [0015]    As shown, the valve assembly  1  is located in a sealing tight manner with the aid of seals  50  in a line through which flows a cooling fluid for example water for cooling a vacuum pump. The valve assembly  1  is so fitted that a space  52  is defined between the upper surface of the member  28  and a facing surface of the line carrying the cooling fluid.  
         [0016]    When the full flow of the cooling fluid is not required, that, when only minimal flow is required the valve assembly  1  will be as shown in FIG. 1. Some fluid from the pump to be cooled or being cooled will pass directly from the inlet  4  via the notches  26 , the hole  14  to the outlet  6  and hence back towards the water return pump. The remainder of the fluid from the pump will pass from the inlet  4  and along the slide-fit between the inner surface of chamber  8  and the outer surface of the body  18  and into the space  52  between the surface of the line carrying the fluid and the member  28  to create a force biasing the main valve  16  downwardly to its closed position. At the same time, the pilot valve is also closed with the bimetallic discs  44  biasing the member (upwardly) as shown so that the valve face  42  engages the seating  36  in a fluid tight manner.  
         [0017]    Thus, in the position shown in FIG. 1 the valve assembly will allow only a minimum quantity of cooling fluid to pass between the inlet  4  and the outlet  6 .  
         [0018]    If now the temperature of the cooling fluid rises beyond a preselected value then the bimetallic discs  44  will move causing the pilot valve to open. That is, the member will follow the movement of the discs downwardly (as shown) so that the valve face  42  will separate from the valve seating  36  thereby allowing the cooling fluid to pass therethrough and then through the holes  41  in the member  40  and hence through the holes  45 ,  22  and  14  to the outlet  6 .  
         [0019]    At the same time, the release of pressure from the fluid in the space  52  above the member  28  will allow the main valve to lift allowing the full flow of fluid between the inlet  4  and the outlet  6  (see FIG. 2).  
         [0020]    The valve assembly  1  will continue to “flip” between the minimum and maximum flow positions to maintain the cooling fluid within a preselected temperature band or control in a mid-position depending on bimetal disc design.  
         [0021]    Preferably, the body  18  is made from brass which readily conducts heat to the discs  44  thereby minimising thermal delay.  
         [0022]    It will be evident that the valve assembly  1  operates in a fluid cooling system to reduce the flow when not required and to open to full flow when needed. This is achieved by the use of the temperature sensitive member for example the bimetallic discs  44  which are sensitive to the temperature of the cooling fluid.  
         [0023]    In a modification a spring may be incorporated to bias the main valve  16  from the full open position (FIG. 2) to the relatively closed position (FIG. 1).  
         [0024]    The valve assembly if mounted directly on to a hot surface of a pump can be used to switch some or all of the fluid flow by sensing the temperature of the surface. In such an application the minimum flow could be zero and this would be achieved by doing away with the notches  26  so that the main valve  16  creates a fluid tight seal when in its closed position.  
         [0025]    The notches  26  offer a particular advantage in that if they were in the form of fixed holes they could be blocked by contaminants carried by the cooling fluid. However, when the valve assembly  1  is open the fluid flow flushes the notches  26 .  
         [0026]    While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.