Abstract:
A valve comprising a housing having an inlet and spaced therefrom an outlet, a passageway extending between the inlet and the outlet, and a mechanism located in the passageway for controlling the flow of a fluid between the inlet and the outlet, the mechanism including a valve assembly movable between a first open position spaced from a co-operating valve seat and a second closed position at which the valve assembly sealingly engages the valve seat, in which the valve assembly is biased towards the second closed position using a magnet-operated mechanism.

Description:
FIELD OF THE INVENTION 
     The present invention relates to valves and in particular to pressure relief valves. 
     BACKGROUND OF THE INVENTION 
     It is known, for example, to locate a pressure relief valve between high and low pressure regions in a pneumatic or vacuum system such valves are actuated at a predetermined differential pressure to relieve the high pressure either to the low pressure region or to atmosphere. This known type of pressure relief valve uses either a spring or sometimes gravity alone to bias a valve stem towards a co-operating valve seat to maintain the valve in a normally closed position. 
     When this type of valve is required to operate free of oscillations it is common practice to incorporate a damping mechanism. The damping mechanism requires components which are manufactured to close tolerances and in environments where condensation and/or solid deposition may be formed within the valve this presents a risk of malfunction particularly with a spring-biased mechanism. 
     SUMMARY OF THE INVENTION 
     It is an aim of the present invention to provide a valve which incorporates a magnetic means for biasing the valve towards its closed position and which operates substantially free of oscillations while maintaining large internal clearances. This permits the valve to operate in environments where condensation and/or solid deposition may occur. 
     According to the present invention, a valve comprises a housing having an inlet and spaced therefrom an outlet, a passageway extending between the inlet and the outlet and means located in the passageway for controlling the flow of a fluid between the inlet and the outlet, the means including a valve assembly movable between a first open position spaced from a co-operating valve seat and a second closed position at which the valve assembly sealingly engages the valve seat, in which magnetic means is provided for biasing the valve assembly towards the second closed position. 
     In a preferred embodiment, at least a portion of the valve assembly is in the form of or incorporates a permanent magnet and a further magnet is located adjacent the valve seat. The further magnet may be a permanent magnet or alternatively an electromagnet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention will now be described, by way of example only, reference being made to the accompanying drawing which is a cross-section of a pressure relief valve according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown, a pressure relief valve  1  includes a housing  2  having an inlet  4  and spaced therefrom an outlet  6 . Located in the passageway extending between the inlet  4  and the outlet  6  is means including a valve assembly  8  and a co-operating valve seat  10  for controlling the flow of a fluid, for example a gas between the inlet  4  and said outlet  6 . 
     The valve assembly  8  depends from a valve cap  9  of magnetic material which is sealingly engaged in the upper (as shown) end of the housing  2 . Surrounding that portion of the valve assembly  8  within the valve cap  9  is a polymer bush  7 . 
     The valve stem assembly  8  includes a valve stem  12  from which extends radially outwardly therefrom a recessed flange  17 . Resting on the upper surface of the recessed flange  17  and surrounding the valve stem  12  are a polymer shock absorber  11  and a magnetic stainless steel washer  13 . 
     Attached to the lower (as shown) end of the recessed flange  17  by means of a fastener  18  is a spherical seal pad  15  and located within the recessed flange  17  above the spherical seal pad  15  is a permanent magnet  14  mounted against a mounting aid  5 . 
     The valve seat  10  is made from magnetic material and adjacent the valve seat on that side of the valve seat opposite the spherical seal pad  15  is a magnet  16  also mounting against a mounting aid  5 . The magnet  16  may be in the form of a permanent magnet or alternatively an electromagnet. 
     As shown, a magnetic stainless steel sleeve  3  depends from the valve cap  9  and surrounds the valve assembly  8 . 
     The pressure relief valve  1  operates between two stable positions, namely fully shut and fully open. With the valve  1  in its fully shut position as shown, fluid is prevented from flowing through the passageway between the inlet  4  and the outlet  6  of the housing  2  since the spherical seal pad  15  sealingly engages the valve seat  10 . The valve  1  will remain shut until the pressure differential between the inlet  4  and the outlet  6  increases to such an extent that an upward (as shown) force is produced on the spherical sealing pad  15  which overcomes both the attractive force between the magnet  16  and the magnet  14  and the weight of the valve assembly  8 . If the upward force produced by the pressure differential equals or surpasses the magnetic force and the weight of the valve assembly  8  then the spherical seal pad  15  separates from the valve seat  10  to allow the passage of gas from the inlet  4  to the outlet  6 . 
     The magnetic force between the spherical seal pad  15  and the valve seat  10  is adjusted to provide a force greater than the weight of valve assembly  8  such that when the pressure differential causes the spherical seal pad  15  to separate from the valve seat  10 , thus cancelling the magnetic force, the valve assembly  8  is lifted clear. The gas flow between the flange  17  and the sleeve  3  produces an upward force greater than the weight of the valve assembly  8  propelling it towards the fully open position against the top cap  9 . 
     With the valve  1  fully open there are three forces involved, namely the weight of the valve assembly  8 , the force produced by the pressure differential across the recessed flange  17  and the magnetic force produced by the magnet  14  and the magnetic top cap  9 . The magnetic force is adjusted to less than the weight of the valve assembly  8  by the relative positions of the magnet  14  and magnetic washer  13  to the valve top cap  9 . This bridge could also be produced by incorporating an electromagnet within or on the top cap  9 . 
     When the force produced by the pressure differential between the flange  17  and the magnetic sleeve  3  is reduced the magnetic force cannot support the weight of the valve assembly  8  allowing it to lose contact with the top cap  9 . The magnetic force between the valve assembly  8  and the top cap  9  becomes negligible as the valve assembly  8  falls downwards on the reduced gas glow until the closing magnetic force shuts the spherical seal pad  15  and the valve seat  10 . 
     The pressure differential to initiate the opening by overcoming the magnetic force is greater than the pressure to move the valve assembly  8  to its fully open position. Similarly, the lower pressure differential required to initiate the closing by allowing the weight to overcome the magnetic force is lower than the pressure differential to keep the valve assembly  8  open and is not sufficient to support the weight of the valve assembly  8 . This allows a free fall of the valve assembly  8  to the shut position. 
     The larger open and lesser closing pressure differentials are separated sufficiently to give a large hysteresis to prevent interactions between opening and closing as well as possible instability. 
     The shock absorber  11  provides a cushioning effect on the top surface of the valve stem assembly  8  to prevent or minimise valve flutter. 
     The polymer bush  7  protects the performance of the valve  1  in hostile-environments by preventing deposition or corrosion on the sliding surfaces of the top cap  9  and the stem  12  of the valve assembly  8 . The main function of the magnetic sleeve  3  is to provide outlet ports and to keep the valve within predetermined boundaries. The fact that it is made from magnetic material prevents any lateral instability by biasing the valve assembly  8  towards the nearest point of the sleeve  3 . 
     The spherical seal pad  15  and the valve seat  10  geometry are arranged such that irrespective of the attitude or eccentricity of the valve assembly  8  in the magnetic sleeve  3  sealing is achieved by toppling onto the valve seat  10  without the necessity of laterally centralising by sliding. 
     The magnetic mounting aids  5  can be in the form of a wavy washer or polymer that absorbs any sudden shock or vibration thereby preventing damage to the permanent magnets  14 ,  16  which are usually brittle. 
     A particular advantage of the above described valve  1  is that the said valve opens at a predetermined pressure differential and remains open with a much lower pressure because once the valve assembly  8  has moved away from the valve seat  10  the magnetic force is reduced significantly. Furthermore, the combination of magnets, magnetic and non-magnetic materials along with the weight of the valve assembly  8  allows the user to tune easily the operating range. This is accomplished by selecting the relative position of the permanent magnets  14 ,  16  and their contact area which forms the actual sealing surface between the valve assembly  8  and the valve seat  10 .