Abstract:
A pinch valve is described wherein the critical flow path is modified to form a space between two opposing metal disks that transition between an open and a closed state. The disks are characterized by a spring constant and act like a diaphragm. A closure force is applied externally to completely close the disks and truncate flow, while providing a substantially perfect seal. Removal of the external force enables the disks to spring open and initiate flow. The pinch valve advantageously eliminates valve bodies, dead space, moving parts and seals, such as elastomers, that are subject to wear and corrosion.

Description:
FIELD OF THE INVENTION 
   The field of the invention relates generally to flow control valves. In particular, the field of the invention relates to a pinch valve wherein the critical flow path is modified to form a transition between opposing metal disks acting like a spring activated diaphragm. The closing force is provided externally to the disks to truncate flow. Thus, particle build-up is completely eliminated within the valve. Also, since the valve mechanism is completely external to the flow passage, degradable components such as moving parts, seals, elastomers, dead space, and valve bodies are advantageously eliminated. 
   BACKGROUND OF RELATED ART 
   Regulating valves have many applications in industry. A wide variety of valves have been developed to serve many different industrial requirements. For some demanding applications requiring high flow rates, high temperatures, corrosive materials or precision cut-off, such as semi-conductor processing, precision instruments, medical, pharmaceuticals, chemical, food processing or the like, existing valve designs are not fully satisfactory. 
   The limitations of existing valve designs can be subtle but vitally important. These limitations include factors such as: materials required (for the valve construction) such as plastics, elastomers, metals etc. which lead to contamination, corrosion, reliability, particles maintenance and cost issues; sliding surfaces which lead to wear particles, contaminating lubricants, cleaning and sanitation difficulties; complex geometry with accompanying purge and cleaning difficulties. Also large size, temperature limitations and high cost are other complicating factors that limit conventional pinch valve design. 
   However, even when cost is no object, it still often can be difficult to provide a pinch valve design that would satisfy all the requirements of industry. Therefore, what is needed is a valve with improved features for demanding applications. For example, it would be desirable for such a value to provide improved throttling and sealing characteristics, low friction losses, high flow rates, and resistance to corrosive materials and high temperature. 
   SUMMARY 
   An aspect of the invention provides a valve wherein the critical flow path is modified to form a space between two opposing metal disks that transition between an open and a closed state. The disks are characterized by a spring constant and act like a diaphragm. A closure force is applied externally to completely close the disks and truncate flow, while providing a substantially perfect seal. Removal of the external force enables the disks to spring open and initiate flow. An aspect of the invention advantageously eliminates valve bodies, dead space, moving parts and seals, such as elastomers that are subject to wear and corrosion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features, aspects and advantages of the invention will become better understood with regard to the following descriptions, appended claims and accompanying drawings in which: 
       FIG. 1  is a simplified cross-sectional diagram of a conventional globe valve; 
       FIG. 2  is a variation of a conventional globe valve of  FIG. 1  wherein a diaphragm is inserted between the seat and shaft tip; 
       FIG. 3  shows a cross-sectional view of a conventional pinch value comprising soft plastic or rubber tubing; 
       FIG. 4  is a cross-sectional view of a pinch value wherein a flow path is modified to transition into an annular space between opposing metal disks in accordance with an aspect of the invention; 
       FIG. 5  is a top view of the valve of  FIG. 4  in accordance with an aspect of the invention; 
       FIG. 6  is a cross-sectional front view of  FIG. 5  showing the disks in an open state in accordance with an aspect of the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a simplified diagram of a conventional design called a “globe” valve. A pressurized inlet for a flow path is usually applied at  1  so that when shaft  3  is applied to seat  6  (in closed position), seal area  4  is not subjected to constant pressure or persistent leakage if seal  4  fails. Flow proceeds to outlet  2  in normal operation. For a vacuum application, ports  1  and  2  are commonly reversed. A vacuum at  1  is protected against risk of leakage at  4 . A variety of threaded connections are commonly used at ports  1  and  2 . A variety of thread structures are commonly present to facilitate motion and sealing of shaft  3 . This motion risks leakage, may require contaminating lubrication, produces wear particles, and is associated with a circumferential cavity or annulus  7  that can collect debris and is difficult to clean. The valve, except for seals, is commonly metal. The shaft tip  5  commonly incorporates an elastomer to improve sealing at seat  6 . The sliding seals, the seal materials themselves and the dead space  7  all tend to be objectionable for demanding applications. Other common valves such as gate, ball, butterfly and petcocks or stopcocks share the same kinds of problems. 
     FIG. 2  shows a variation on  FIG. 1  wherein a diaphragm  8  is inserted between seat  6  and shaft tip  5 . This is the principle of a diaphragm valve. A threaded compression seal or weld seal at  10  completes the diaphragm installation. This means that particles, contamination or leak risk associated with shaft  3  are eliminated from the fluid flow path from  1  to  2 . 
   However, the annulus  7  still remains. Also, the sealing portion  9  of the diaphragm may still require an elastomeric surface against seat  6  as well as the twisting force of  3  against sealing portion  9  in the valve closing process. 
   The body  11  of either valve may be undesirably large as well as expensive for replacement, particularly if high-grade design, construction and materials are involved. 
   If the plumbing material is soft plastic or rubber, as tubing  12  in  FIG. 3 , a very simple pinch valve can be utilized as shown. Clamps  13  pinch the tubing  12  to restrict or completely stop fluid flow. 
   This pinch valve is very commonly used in hospitals for intravenous food or medication flow control. The design of such a conventional pinch valve is simple, effective and inexpensive, requiring no seals or sliding parts, no lubrication, no dead spaces (such as annulus  7 ) and the valve mechanism is totally external to the flow passage (no counter part to body  11 ). 
   For some medical applications, the conventional pinch valve of  FIG. 3  may be entirely compatible. For many other industrial applications, however, rubber or plastic,  12 , would be entirely unacceptable and must be replaced by carefully chosen, fabricated and cleaned tubing such as stainless steel. But since stainless steel is so rigid and inflexible, a conventional pinch valve such as in  FIG. 3  would be impracticable if not impossible to implement. 
   Referring  FIGS. 4 and 5 , in accordance with an aspect of the invention, a flow path  14  defined by metallic tubing  15  is modified to transition into an annular space  16 . Viewed from above, as shown in  FIG. 5 , annular space  16  forms annular mating surfaces or opposing disks  18  characterized by a spring action. Such spring action in opposing disks  18  provide improved throttling characteristics of fluid in flow path  14 , and sealing of the flow path  14  can be obtained without introducing complex or contaminating control surfaces. Referring to  FIG. 4 , metallic tubing  15  forms a flow path  14  for a flowable material. A first tubular channel  20   a  or portion of tubing  15  defines an entry flow path. A second tubular channel  20   b  or portion of tubing  15  forms an exit flow path. The entrance and exit flow paths of tubing  15  are modified to transition in a taper into annular space  16  that acts as a closure region defined by the two opposing annular mating surfaces or disks  18 , characterized by a spring action. It is important to transition the flow paths  20   a ,  20   b  gradually into and out of the closure region, respectively, to maintain laminar flow as much as possible and to prevent formation of turbulent flow. The interior, fluid contacting surface of disks  18  comprise mating sealing surfaces that form the closure region and completely truncate flow through annular space  16 , when the sealing surfaces of opposing disks  18  are seated against each other. 
   Disks  18  transition between a closed and open state depending on the application of an external force  22  by clamps  24 , or an internal force applied by a positive pressure of the material flowing through the flow path defined by tubing  15 . In assembly, disks  18  are sealed or welded at their edges to the tubing  15 , at the point where the tubing transitions into the annular space formed by the disks  18 . The disks  18  interoperate to act like a spring activated diaphragm. 
   It is important that the interior mating surfaces of disks  18  that define the control surface for closure of the flow path are characterized by extreme surface smoothness without any asperities. This enables complete truncation of flow without any leaks when the disks  18  are seated against each other in the closed state. Clamps  24  and force  22  are applied to the metallic disks  18  of  FIGS. 4 and 5  to create a control surface that completely truncates the flow path. Because of the flexibility provided by disks  18 , there are no particles, moving parts, seals, elastomers, dead spaces or valve bodies interposed in the flow path; and the valve mechanism is totally external to the flow passage. 
     FIG. 6  is a further illustration of the structural principle of the pinch value according to an aspect of the invention.  FIG. 6  is a cut-away view of  FIG. 5  without the clamps  24  in place. The disks  18  are curved slightly in the relaxed (i.e. open) condition. The curve is chosen so the clamping or closing process (flattening) does not exceed the yield or spring point of the disk material. By so doing, when the clamps are loosened from the flat or closed position, the disks spring open to provide a flow path  14  as shown in  FIG. 6 . The disks are also strong enough to spring open whether the pressure inside tubing  15  is positive or negative. The disks  18  are comprised of any metal that is capable of maintaining a spring action over many thousands of transitions between a closed and open state. Preferably the metal can be selected so as to be non-reactive with the material in the flow path. 
   Alternatively, the annular mating surfaces  18  including their respective tapered entry and exit paths and/or clamps  22  may be fabricated from a shape memory alloy such as titanium nickel. In this case, the opposing closure sections and/or their respective clamps are pre programmed to deform in a desired orientation with respect to each other so as to form a fluid tight seal between interior surfaces of disks  18  in the closure region upon reaching an activation threshold and phase change. For example clamps  22  could comprise resistive heating elements constructed in accordance with techniques that are well known. The application of an electric current through resistive heating elements provided around the closure region may be used to activate the phase transition and assumption of a preprogrammed shape for effecting closure and a fluid tight seal between interior surfaces of disks  18 . In most shape memory alloys, a temperature change of only about 10° C. is necessary to initiate the phase change and assumption of the pre programmed shape. The most effective and widely used alloys include NiTi (Nickel-Titanium), CuZnAl, and CuAlNi. 
   Shape memory alloy tubing is available from, for example, MicroGroup, Inc., 7-T Industrial Park Rd. Medway, Mass. 02053. In all such equivalent arrangements, the closure region is tapered into the respective entry and exit flow paths to maintain laminar flow, Also, the closure mechanism, for example resistive heating elements, that effects a fluid tight seal by activating the mating of the sealing surfaces is external to the flow path and is not adversely affected by fluid flow. 
   While the invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.