Patent Publication Number: US-2009217988-A1

Title: Dual seal valve

Description:
FIELD OF THE INVENTION 
     The present invention relates broadly to a valve and relates particularly, although not exclusively, to a non-return valve, check valve or back flow prevention device or valve. 
     BACKGROUND OF THE INVENTION 
     Back flow valves, non-return valves and check valves are used throughout plumbing systems. Check valves of a duckbill configuration are relatively well known and used in the art of valves. The patent literature has a large number of patents disclosing duckbill valves including U.S. Pat. Nos. 3,901,272, 4,524,805, 3,822,720, 4,240,630 and 6,089,260. These patents similarly disclose a valve of a duckbill form having a slit at its outlet. The slit is designed to elastically deform and open when tension is applied about is periphery whereas closure of the slit is automatically provided by biasing stresses in the valve as a consequence of its shape. 
     The prior art of U.S. Pat. No. 996,588 and German patent no. 4,033,818 describe variants of the duckbill check valves of the preceding art. Both U.S. Pat. No. 996,588 and DE 4,033,818 are valves of a generally conical shape designed to permit flow in a single direction only. U.S. Pat. No. 996,588 is a check valve with a transverse slit through a relatively thick apex portion of the valve which is tensioned under fluid pressure to elastically deform and open. DE 4,033,818 is a pressure relief valve having a discharge aperture at its apex which opens and releases pressure at a predetermined pressure. The valve of DE 4,033,818 is constructed of a highly elastic synthetic resin or rubber which is biased closed but under pressure is stressed about the discharge aperture which is opened. 
     The applicants (or their predecessors) of international patent application no. PCT/AU00/00659 disclose a non-return valve having a valve diaphragm of a conical-shape. The valve diaphragm which is constructed of a resiliently flexible material includes a collapsible aperture which is exposed so as to open under fluid pressure on an upstream side of the valve. The valve diaphragm is tensioned or stressed about the collapsible aperture and the wall thickness of the diaphragm is reduced toward its apex to facilitate this opening of the valve. 
     These check or non-return valves suffer from at least the following problems:
         (i) the differential pressure required across the valve to effect its opening is relatively high;   (ii) the valve may be designed to reduce this differential pressure for opening but then has a tendency to leak (reverse flow) at relatively low differential pressures; and   (iii) the valve in its open condition does not provide great flow throughputs as the throat restriction of the slit or collapsible opening is relatively high.       

     SUMMARY OF THE INVENTION 
     According to one aspect of the invention there is provided a valve comprising: 
     a valve housing including a valve seat; 
     a valve head movably housed within the valve housing for seating with the valve seat; and 
     a lip seal connected to either the valve head or the valve seat and being configured to be hydraulically biased into contact with the valve seat or the valve head to maintain closure of the valve. 
     Preferably the lip seal is hydraulically biased into contact with the valve seat or the valve head to maintain closure of the valve at relatively low differential pressures across the valve head. 
     According to another aspect of the invention, there is provided a valve comprising: 
     a valve housing including a valve seat; 
     a valve head movably housed within the valve housing for seating with the valve seat; and 
     a pair of seals each being connected to either the valve head or the valve seat, one of the pair of seals being a supplementary seal biased at least in part by fluid pressure on its underside to maintain closure of the valve on at least partial unseating of the other of the pair of seals from the valve seat or the valve head. 
     Preferably the supplementary seal is additionally biased at least in part by a resiliently deformable seal portion. Preferably the supplementary seal is in the form of a lip. 
     Preferably the lip seal is inclined at an acute angle to an attaching surface defining a pressure cavity. More preferably the cavity is defined by an underside of the lip seal. Even still more preferably the lip seal is attached to the valve head. 
     Preferably the other of the pair of seals is a compression seal. More preferably the compression seal is a half O-ring type seal. 
     Preferably the lip seal and the compression seal are both formed integral with the valve head. More preferably the lip seal protrudes beyond the compression seal for contact with the valve seat prior to seating of the compression seal on closure of the valve. 
     Preferably the valve head includes a stop to prevent over-compression of the supplementary seal. More preferably the stop is the other seal. 
     Preferably the valve also comprises a valve opening formed about an inner surface of the valve seat. More preferably the valve opening is in the form of an orifice and the supplementary seal or the lip seal is located adjacent the orifice when the valve is closed. More preferably the lip seal is inclined towards the orifice when the valve is closed. Still more preferably the other seal is located radially outside the supplementary seal. 
     Generally the valve is a non-return valve. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES  
       In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a valve will now be described in some detail, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view of one embodiment of a valve according to the invention, the valve being closed; 
         FIG. 2  is a cross-sectional view of the same embodiment of the valve according to the invention, the valve being opened; 
         FIG. 3  is a cross-sectional view taken through AA of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view taken through BB of  FIG. 2 ; and 
         FIGS. 5-12  illustrate finite element analysis data showing opening of a valve in another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 1 and 2  depict one embodiment of a valve generally depicted as  10  according to the invention. The valve in this example is a water valve of a non-return type  10  comprising a valve housing  14  including a valve seat  12 . In this embodiment, the valve seat is defined by an inwardly directly annular flange  12 . The valve assembly  10  also comprises a valve head  16  which contacts the valve seat  12  for closure of the valve assembly  10 . The valve assembly  10  further comprises biasing means in the form of an elongate bellows  18  connected to the valve head  16 . As shown in  FIG. 1 , the bellows  18  is resiliently deformable and pre-stressed, or slightly compressed in its closed state within the valve housing  14 , so that it urges the valve head  16  towards and into sealing contact with the valve seat  12 . 
     The flow of fluid  20  in a forward direction through the open valve assembly  10  is shown in  FIG. 2 . Force or pressure from the fluid  20  applied to the valve head  16  from the direction of the valve seat  12  unseats the valve head  16  allowing the fluid  20  to pass through the valve assembly  10 . The opening of the valve  10  is effected provided the force exerted by the fluid  20  is greater than the force exerted in an opposite direction by the bellows  18  combined and by fluid pressure in a reverse flow direction  22 . 
     As shown in  FIG. 1 , the valve head includes a pair of integrally formed seals. One of the seals is a half O-ring type seal  28  for contact of the valve seat  12  on seating of the valve head  16 . The sealing is enhanced as the force exerted by the reverse fluid flow  22  on valve head  16  increases. In another embodiment not shown here, the half O-ring type seal  28  comes to a point for contacting the valve seat  12 , the point deforming under small loads to comply with a rough valve seat  12 . 
     The valve head  16  also includes a supplementary seal in the form of a lip seal  30  formed of a resiliently deformable material. As shown in  FIG. 2 , the lip seal  30  is, in this embodiment, thin and flexible, and tapers to a knife-like edge  41 . In this example, the manufacture of the knife-like edge is achieved by injection of a settable material into a two part mould. When the valve is open the lip seal  30  protrudes beyond the compression seal  28 . The lip seal  30  is located adjacent a valve opening or orifice  29  formed about an inner surface of the valve seat  12  of the closed valve. The lip seal  30  is inclined at an acute angle of about 10-60 degrees to the valve head  16 , defining a pressure cavity  39 . The lip seal  30  is inclined towards the orifice  29  when the valve  10  is closed. At least part of the lip seal, and preferably all of it, defines a resiliently deformable seal portion  30  that at least in part biases the lip seal  30  towards the valve seat  12 . The lip seal  30  has an underside  32 , defining the pressure cavity  39  for receiving a portion of the fluid  20  on closure of the valve  10 . The fluid urges the lip seal  30  into sealing contact with the valve seat  12 , that is, the lip seal  30  is hydraulically biased into contact with the valve seat  12 . The seal is formed by the contact of an outer surface  34  of the lip seal  30  with the valve seat  12 . 
     For small forward pressures, the resilient lip seal  30  maintains closure of the valve as the valve head  16  moves away from the valve seat  12 . Also, prestressing of the bellows  18  acts to push the valve head  16  in contact with the valve seat  12 , to close the valve. The holding pressure of the valve is determined by the strength of these two mechanisms together. In the preferred embodiment the forward holding pressure is at least 0.5 kPa and preferably from 2 to 10 kPa. It will be appreciated that at least in the preferred embodiment, the configuration of the lip seal  30  is such that the hydraulic biasing maintains closure of the valve  10  when the forward flow fluid pressure  20  is slightly higher than the reverse flow fluid pressure  22 . The cavity  39  in effect captures the fluid or water at low pressure and forces the lip seal  30  against the valve seat  12 . 
     The seal formed by the contact of the lip seal outer surface  34  with the valve seat  12  is maintained on at least partial unseating of the O-ring type seal  28 .  FIGS. 5 to 12  illustrate the action of the lip seal  30  as another embodiment of the valve  10  opens.  FIG. 5  shows the valve  10  under high back pressure. Both seals  28  and  30  contact the valve seat  12 .  FIG. 6  shows the closed valve  10  with decreased back pressures.  FIG. 7  shows the valve with no pressure differential across the valve head  16 . Here, only the pre-stressing of the bellows  18  is forcing closure of the valve  10 .  FIGS. 8 and 9  show the valve when the forward flow pressure is slightly greater that the reverse flow pressure, but the pressure differential is still less than the holding pressure of the valve  10 , this typically being from 0.5 to 10 kPa. The lip seal  30  is still in sealing contact with the valve seat  12  even though the O-ring type seal  28  no longer contacts the seat  12 . As the forward pressure increases, the angle that the lip seal  30  makes with the valve head  16  increases, and the lip seal  30  moves away from the valve head  16 .  FIGS. 10 to 12  show the valve opened by a forward pressure greater than the holding pressure of the valve  10 . Neither seal  28  or  30  are in contact with the valve head  12 . 
     As illustrated in  FIG. 5 , the O-ring type seal  28  also acts as a stop for limiting compression of the lip seal  30  at high fluid pressures, preventing damage of the lip seal  30 . The O-ring type seal  28  is located radially outside the lip seal  34 . 
     In some other embodiments not illustrated here, the O-ring type seal  28 , the lip seal  30  or both of these seals are connected to the valve seat  12  instead of the valve head  16 . 
     In this embodiment, the valve assembly  10  also comprises a support member  36  connected to the bellows  18  at an opposite end to the valve head  12 . The support member  36  is shown in cross-section in  FIG. 3 . The support member  36  includes an inner central opening  46  for equalisation of fluid pressure inside and outside the bellows  18 . This pressure equalisation reduces the likelihood of the bellows  18  being deformed or distorted by fluid pressure. 
     The support member  36  is mounted within the valve housing  14  by mounting means  38 . In this embodiment the mounting means  38  is detachably connected by way of a screw thread  40  cut into both the valve housing  14  and the mounting means  38 . The mounting of the support member  36  allows for the pre-stressing of the bellows  18 . In this embodiment the support member  36  includes an outer ring member  42  housed coaxially within the valve housing  14  and a plurality of radial members in the form of radial ribs, such as  44  defining outer fluid openings, such as  48 . The outer fluid openings  48  are a continuation of the fluid passageway  26  outside the bellows. 
     In one embodiment of the invention (not shown), the support member  36  has a screw thread on its outside circumference. This enables the support member  36  to be detachably connected to the threaded valve housing  14  without the use of separate mounting means such as  38 . It will be appreciated that other methods of mounting the support member, such as a bayonet mount, or a press fit could also be used. 
     In another embodiment (not shown), the valve housing is a cartridge or cage. The cartridge or cage may be split longitudinally and hinged for insertion of the valve head  16 , bellows  18  and support member  36 . It will be understood that the cartridge makes installation of the water valve assembly simpler. 
     As shown in  FIG. 4 , the valve head  16  includes guiding means which in this embodiment are radial protrusions in the form of spokes  24  connected to and radiating outwardly from the valve head  16 . The guiding means or spokes  24  ensure that the valve head  16  remains coaxially aligned with the valve housing  14  during sliding movement of the valve head  16  within the housing  14 . The use of relatively thin spokes  24  reduces obstruction of a fluid passageway  26  that is formed between the resiliently deformable bellows  18  and the valve housing  14 . The fluid  20  that flows through the valve assembly  10  flows through the fluid passageway  26  outside the bellows  18 . 
     In the illustrated embodiment, the valve assembly is a cylindrical valve assembly  10  having the valve head  16  and bellows  18  housed coaxially within the valve housing  14 . Furthermore, in this embodiment the valve head, bellows and base portion are of a unitary design. 
     Now that a preferred embodiment of the invention has been described, it will be apparent that it has the following advantages:
         (i) the valve assembly has minimal leakage and remains closed at relatively low differential pressures;   (ii) the differential pressure required across the valve assembly to effect its opening is relatively low;   (iii) the valve assembly is highly resistant to reverse flow pressures; and   (iv) the valve assembly in its open condition allows relatively high flow throughputs.       

     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. For example, the valve assembly may be of a square rather than cylindrical cross-section, and the valve head, bellows and support member may be separable rather than being of a unitary design. The sealing arrangement of the valve may vary from that described, for example:
         (i) the valve may include a single lip seal only;   (ii) the valve may include a pair of lip seals (without the O-ring type seal) of the same or different configurations.       

     The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 
     It is to be understood that any acknowledgment of prior art in this specification is not to be taken as an admission but this acknowledged prior art forms part of the common general knowledge in Australia or elsewhere.