Abstract:
This invention relates to a pressure compensating valve and more particularly, but not exclusively, to a balanced pressure compensating valve, or regulator. The valve includes a chamber ( 6 ) for containing fluid, defined by a flexible barrier ( 2 ) trapped between first ( 3 ) and second ( 4 ) surfaces. A fluid inlet provides fluid to the interior of the chamber. A fluid outlet selectively allows fluid to pass out of the chamber. Movement of the first ( 3 ) and second ( 4 ) surfaces relative to each other causes change in contact between the flexible barrier and the first and second surfaces to selectively open the fluid outlet, in a first position, and occlude it between the flexible barrier and one of the surfaces, in a second position.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a pressure compensating valve and more particularly, but not exclusively, to a balanced pressure compensating valve, or regulator. 
   BACKGROUND ART 
   Pressure compensating valves are widely used in the supply of gases and liquids from a high pressure supply to a low pressure user. It is often desirable to maintain the low pressure side of the valve at a substantially constant pressure irrespective of pressure fluctuations on the high pressure side of the valve. Balanced pressure compensating valves are known for this purpose. 
   Existing balanced pressure compensating valves are relatively expensive, complex and difficult to manufacture and service. The present invention is directed to a pressure compensating valve which can, at least in preferred embodiments, be made in a very simple form at low cost and with good performance characteristics. 
   SUMMARY OF THE INVENTION 
   The invention is a pressure compensating valve including: A chamber for containing fluid, defined by a flexible barrier trapped between first and second surfaces. A fluid inlet to provide fluid to the interior of the chamber. And a fluid outlet to selectively allow fluid to pass out of the chamber. Movement of the first and second surfaces relative to each other causes change in contact between the flexible barrier and the first and second surfaces to selectively open the fluid outlet, in a first position, and occlude it between the flexible barrier and one of the surfaces, in a second position. 
   The flexible barrier may comprise of any one of a number of forms. In one arrangement the barrier may comprise a tube positioned between the first and second members and trapped by the friction between the barrier material and the surfaces. 
   The fluid inlet may pass through the first surface into the chamber. In this case the flexible barrier may be generally U-shaped in section with both ends connected to the first surface on either side of the fluid inlet. 
   The fluid outlet may include an aperture in the flexible barrier which is selectively occluded by one of the surfaces in the second position. 
   There may be a passage between the chamber and the second surface, in which case the fluid outlet may include an aperture in the second surface which is selectively occluded by the flexible barrier in the second position. In this arrangement the flexible barrier may comprise a pair of spaced apart membranes which extend between the surfaces, one on each side of the chamber. The membranes may be connected to the first surface on either side of the fluid inlet, and to the second surface on either side of the passage between the chamber and the second surface. 
   In its simplest form the valve may act as a one way pressure compensated valve controlling the inflow of high pressure fluid through the valve to a user, whether a human or a mechanical device. 
   The valve may further comprise an exhaust aperture in one of the first or second surfaces, which is selectively occluded by the flexible barrier in the first and second positions, but open in a third position. In the third position the fluid outlet is occluded. In this way the valve may control both the supply and exhaust of the fluid supply. 
   Whether the first and second surfaces are flat or curved, relative movement of the two surfaces parallel to each other may cause the flexible barrier to roll along the surfaces to selectively open the fluid outlet. 
   In an alternative the flexible barrier may have a flap-like extension which serves to open and occlude the fluid outlet. 
   The valve may further comprise a pressure plate connected to one of the first or second surfaces. In use, the pressure plate experiences a variable working pressure on an enclosed side, for instance inside a face mask, and a reference pressure on the other side. The pressure differential across the pressure plate causes movement of the first and second surfaces relative to each other to selectively supply fluid to the enclosed side. 
   The reference pressure may be atmospheric pressure or some other pressure. When the valve is used in breathing apparatus, other than diving apparatus, the reference pressure will conveniently be atmospheric. During exhalation, when the working pressure exceeds a predetermined relationship with atmospheric pressure, the pressure plate will be moved towards the reference pressure side of the valve causing the flexible barrier to be rolled over, and occlude, the outlet aperture. Conversely when the working pressure drops, during inhalation, the pressure plate will move in the opposite direction and the outlet aperture will be opened. 
   In some arrangements the area of the flexible barrier exposed to the working pressure and the reference pressure is equal so that any change in pressure in the fluid supply will not cause the second surface to be moved by differential force on opposed sides of the barrier. In other situations it may be desirable to deliberately utilise different exposed areas on each side of the barrier to bias the second surface towards a desired position. 
   The valve may further comprise a bias spring associated with the pressure plate to bias the first and second surfaces into predetermined position relative to each other. In particular the spring may serve to bias the second surface, relative to the first surface, with a defined force into an open position. In this arrangement the valve will be biased into an open position by the spring until the pressure in the mask exceeds that of the surrounding atmosphere by an amount that causes a force to be applied to the one side of the second member to move it, against the spring force, to the closed position. 
   The chamber may be toroidal, the first and second surfaces may be concentric cylinders, the fluid inlet may be an annular chamber formed on the outer surface of the outer cylinder, and the pressure plate may span the interior of the inner cylinder. 
   The first and second surfaces may be conveniently formed by injection moulding of a synthetic plastics material, and the flexible barrier may be formed of a suitably flexible rubber or synthetic plastics material. As the valve may be made from only few pieces, and from relatively cheap materials, it can be seen that it may offer significant manufacturing and cost advantages over known pressure compensating valves. 
   Valves according to the present invention are particularly useful in powered air purifying respirators. Such apparatus may be supplied by air pumped by means of a fan through a suitable filter. Alternatively the respirator may be of a self-contained type for use either underwater or where filtering of the ambient air is inappropriate. 
   When a pressure compensating valve according to the present invention is used in powered air purifying respirators it may control only the inhalation of air by the user or both inhalation and exhalation. In the former case the respirator will need to incorporate another exhaust valve of some sort. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Several examples of the invention will now be described with reference to the accompanying drawings, in which:— 
       FIG. 1   a  is a schematic diagram illustrating a simple form of the invention in a first position; and  FIG. 1   b  is a schematic illustration of the second position. 
       FIG. 2   a  is a schematic diagram of another simple form of the invention in a first position;  FIG. 2   b  is a schematic illustration of the second position: and  FIG. 2   c  is a schematic illustration of a third position. 
       FIG. 3   a  is a vertical section through a pressure compensating valve embodying the invention in a first position;  FIG. 3   b  shows a second position; and  FIG. 3   c  shows a third position. 
       FIG. 4   a  is a vertical section through an alternative pressure compensating valve embodying the present invention in a first position;  FIG. 4   b  shows a second position; and  FIG. 4   c  shows a third position. 
       FIG. 5   a  is a vertical section through yet another pressure compensating valve embodying the present invention in a first position;  FIG. 5   b  shows a second position; and  FIG. 5   c  shows a third position. 
       FIG. 6   a  is a vertical section through yet another pressure compensation valve embodying the present invention in a first position;  FIG. 6   b  shows a second position; and  FIG. 6   c  shows a third position. 
       FIG. 7   a  is a vertical section through a pressure compensating valve embodying the present invention in combination with a separate exhaust valve, in a first position;  FIG. 7   b  shows a second position; and  FIG. 7   c  shows a third position. 
       FIG. 8  is a vertical section through a fan driven powered air purifying respirator incorporating the pressure compensating valve of  FIG. 3 . 
       FIG. 9  is a vertical section through a breathing apparatus style respirator supplied with high pressure air and incorporating a conventional regulator and the pressure compensating valve of  FIG. 3 . 
       FIG. 10  is a vertical section through a breathing appartaus style respirator supplied with high pressure air and incorporating a different regulator and the pressure compensating valve of  FIG. 3 . 
   

   The same reference numerals have been used throughout the drawings to refer to corresponding features. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1   a  shows a pressure compensating valve  1  comprising a tube of flexible material  2  trapped between a first planar surface  3  and a second planar service  4 . 
   A series of holes  5  extending along the upper side of the flexible tube  2  penetrate through its walls. The tube  2  itself defines a chamber  6  into which fluid is pumped, from a source which is not shown. In the position shown in  FIG. 1   a  the fluid cannot escape from the chamber  6  but remains there at supply pressure. 
   When the upper planar surface  4  moves to the left with respect to the lower planar surface  3 , as indicated by arrow  7  in  FIG. 1   b , the line of holes  5  are rotated anti-clockwise as friction between the tube  2  and the planar members causes it to roll between the planar surfaces. Once the holes clear the upper planar surface  4 , fluid may flow through holes  5  from the relatively high pressure within chamber  6  to the relatively low pressure area indicated at the end of arrow  8 . 
   If a reference pressure is provided to the right hand side of the valve arrangement, and a working pressure is applied to the left hand side of upper plate  4 , then a reduction in the working pressure will cause the movement indicated by arrow  7  causing fluid to enter the chamber. Conversely, an increase in the working pressure will move planar surface  4  to the right and close the valve. 
   In  FIGS. 2   a  and  2   b , a very similar valve  1 ′ is shown. In this valve there are a second series of holes  9  extending through the lower plate  3  below the flexible barrier  2 . 
   In the first position shown in  FIG. 2   a , the supply fluid cannot escape tube  2 . In the second position of  FIG. 2   b  where the upper planar surface is moved to the left fluid is supplied through holes  5  to the left as indicated by arrow  8 . In the third position of  FIG. 2   c , movement of the upper planar surface  4  to the right as indicated by arrow  10  closes holes  5  against upper planar surface  4 , and maintains them closed as the plate  3  is moved sufficiently to open holes  9 , allowing exhaust to flow back in the direction  11 . 
   This valve therefore provides the ability not only to supply fluid, but also to exhaust spent fluid. When the valve is used in breathing apparatus an atmospheric reference pressure is applied to the right hand side of the valve, and a working pressure in a face mask acts on the left hand side of upper planar surface  4 . The upper planar surface  4  will move to the left, as indicated by arrow  7  in  FIG. 2   b , when the working pressure falls during inhalation, and to the right, as indicated by arrow  10  in  FIG. 2   c , as the pressure rises during exhalation. 
   The apparatus shown in  FIGS. 1 and 2  may be rolled up so that the tube  2  comprises a torus as shown in the remaining Figures. The lower planar surface  3  becomes the outer cylindrical wall of a movable valve member  12 , and the upper planar surface  4  becomes the inner surface of an annular air supply duct  13 . Depending upon the construction the inner, moveable, cylindrical member  12  is closed by an internal wall  14  which prevents fluid from passing through the member and provides a pressure plate. To the right of pressure plate  14  is atmospheric pressure, and to the left, which is inside the face mask  15 , there is a variable working pressure. 
   Referring particularly to  FIGS. 3   a ,  3   b  and  3   c , the pressure compensating valve shown comprises an injection molded synthetic plastics housing  16  which defines annular duct  13 . The movable member  12  is also formed of injection molded plastics material. The housing  16  includes a spigot  17  for connection to an air supply. Air entering through spigot  17  communicates with the annular duct  13  and via a slot  18  which extends around the full inside radius of housing  16 , into chamber  6  bounded by the flexible barrier  2 . 
   In this embodiment, the flexible barrier  2  comprises an inner flexible membrane  19  and an outer flexible membrane  20 . Membrane  19  is connected along one end  21  to the left hand edge of slot  18 , and along the other end  22  to the surface  3  of moveable member  12 . And flexible membrane  20  is connected along one end  23  to the right hand edge of radial slot  18 , and along the other end  24  to the surface  3  of inner member  12  adjacent the inner membrane  19 . The membranes  19  and  20  are preformed with a U-shaped section and they are arranged so the arms of the ‘U’ lie against either the inner surface  4  of outer housing  16  or the outer surface  3  of inner member  12 . A series of holes  5  penetrate the inner membrane  19  close to its end  22  adjacent the moveable member. 
   A bias spring  25  urges movable member  12  to the left so that the movable member is in a position shown in  FIG. 3   a . In this condition, air under substantially greater then atmospheric pressure is supplied through spigot  17  via annular duct  13  into the interior  6  of the chamber bounded by flexible membranes  19  and  20  and out through holes  5  into the breathing mask  15 ; as indicated by arrows  8 . The flexible membrane  19  also occludes the series of holes  9  around the inner cylindrical extension  26  of outer member  16 . 
   When the user stops inhaling, pressure within the mask  15  rises just sufficiently to balance the force of the spring  25 , and valve member  12  moves to the position shown in  FIG. 3   b . In this condition the holes  5  in the inner membrane  19  are occluded by the exterior surface  3  of moveable member  12 . The series of holes  9  around the inner cylindrical extension of outer member  16  also remain occluded by the other end of membrane  19 . 
   As the user starts to exhale the pressure in face mask  15  rises and acts upon pressure plate  14  to drive movable member  12  further to the right, as indicated in  FIG. 3   c . As this happens flexible membrane  19  moves away from the series of holes  9  to enable the exhalation to exhaust to atmosphere, as indicated by arrows  11 . 
   The arrangement shown in  FIG. 4  operates in essentially the same way as that shown in  FIG. 3 , however, in this case the exhaust apertures  9 , instead of being placed around the circumference of the outer member  16  are placed around the outer circumference of the right hand end of movable member  12 , that is in the right hand side of surface  3 . In the first and second positions shown in  FIGS. 4   a  and  4   b  the exhaust holes  9  are occluded by the flexible membrane  20 . However, in the third position shown in  FIG. 4   c  the movable member  12  is moved sufficiently far to the right that flexible membrane  20  has drawn away from holes  9  and opens the exhaust path  11 . 
   In  FIG. 5  operation is a little more complicated by the inclusion of a passageway  26  extending from the interior of chamber  6  into the interior of member  12 . In this case, inlet holes  5  are provided around the left hand end of the outer cylindrical housing  3  of movable member  12 . In other words, in the left hand side of surface  3 . As shown in  FIG. 4 , the exhaust openings are in the right hand side of surface  3 . 
   In the first position, shown in  FIG. 5   a , air flows through spigot  17  into the annular space  13 , through slot  18  into chamber  6 , then through passageway  26   a  into the interior of member  12  and out through holes  5  into mask  15  as indicated by arrows  8 . The holes  5  are occluded by the inner membrane  19  in the second position shown in  FIG. 5   b , and they remain occluded in the third position shown in  FIG. 5   c . However, the exhaust openings  9 , which are occluded by flexible member  20  in the first and second position shown in  FIGS. 5   a  and  5   b , are open in the third position shown in  FIG. 5   c.    
   In  FIG. 6 , the tubular barrier  2  is formed of a single membrane attached at both its ends to either side of slot  18  in the outer member  16 . 
   An extension flap  27  extends radially inward from tubular barrier  2 , and lies along the outer surface  3  of inner member  12 . The distal end of flap  27  is attached into a groove  28  which extends around the circumference of surface  3 . 
   A series of openings  5  extend around the inner side of membrane  2  between the point of connection of flap  27  and the connection to the left hand edge of slot  18 . Inhalation operates in the same fashion as in  FIGS. 3   a  and  4   a , with the exhaust apertures  9  being closed by flap  27  which overlies them. As the inner member  12  moves to the right, to the second position shown in  FIG. 6   b  flap  23  stills overlies holes  9 , but as the inner member  12  continues to move to the right, flap  23  is drawn away from apertures  9  as its point of attachment  28  to member  2  is drawn away from surface  3 , to allow exhaust along path  11 . 
     FIG. 7  shows an alternative arrangement in which the inlet path is similar to that as shown in  FIG. 5 , but an additional exhaust valve  29  is provided inside face mask  15 . The exhaust valve  29  comprises a flexible circular diaphragm  30  connected at its periphery to an inner cylindrical extension  31  of housing  16 . 
   Radially inwards of its connection to housing  16  the diaphragm  30 , when in the relaxed condition, abuts against a circular shoulder  32  on the housing  16 . An inlet flap valve  33  is provided in diaphragm  30  within the area bounded by shoulder  32 . 
   In use, air under substantially greater then atmospheric pressure is supplied through spigot  17  into the duct  13 . This air will initially find the valve in the condition as shown in  FIG. 7   a  due to the force of bias spring  25  which urges movable member  12  to the left. In this position air flows through the inlet ports  5  in the left hand end of the outer circumference of movable member  12  and through holes in diaphragm  27  underneath flap valve  29  into space bounded by mask  15 . 
   When the user stops inhaling, pressure builds inside mask  15 , and when it rises just sufficiently to balance the force of spring  25 , the movable valve member  12  moves to the condition shown in  FIG. 7   b  and flap valve  33  closes. 
   As the user starts to exhale, the pressure inside the mask increases, and causes diaphragm  30  to move to the right away from shoulder  32 . Air can then flow past shoulder  32  and exhaust through the exhaust ports  9 , as shown in  FIG. 7   c  by the arrows  11 . 
   The pressure compensating valve may be connected to a fan driven air blower  34  in a fan forced positive air pressure breathing apparatus, as shown in  FIG. 8 . The fan communicates with the valve through a wide diameter hose  35 . 
   The pressure compensating valve may alternatively be connected to an air supply such as a compressed air cylinder  36  like a self-contained breathing apparatus, or alternativenly to an industrial pressurised air supply through a regulator  37 , as shown in  FIG. 9 . In this case a narrow diameter high pressure hose  38  connects the air cylinder to the regulator. The regulator is, in turn, connected to valve through a wide diameter hose  35  as before. 
   The pressure compensating valve may also be connected to an air supply such as a compressed air cylinder  36  through a regulator  37  in a self-contained breathing apparatus. In this case two narrow diameter hoses  39  and  40  and connect the regulator with the valve. One of the hoses acts as a pilot hose conveying to the regulator the pressure on the inlet side of valve. 
   It should be appreciated that the pressure compensating valve may be embodied in many other ways besides those described above. For instance, although all the embodiments show a valve having a generally circular configuration it could work equally well with other configurations such as oval or even square. Where a circular configuration is employed the surfaces need not be cylindrical but could be conical. Alternatively, a linear configuration could be envisaged where the flexible barrier is straight and has a connection at either end to a hinge that lies parallel to its axis. Depending on the configuration the flexible barrier may roll, stretch or deform as the two surfaces move relative to each other to open and occlude the fluid outlet. 
   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. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.