Patent Publication Number: US-2023151899-A1

Title: Mechanical valve for pressure control

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to pressure regulation in fluid systems, and more particularly to mechanical valves for pressure regulation. 
     Known types of gas systems, such as medical equipment, require pressure regulation or pressure relief at low pressures, for example in the range from 5 to 100 mbar. 
     The majority of prior art systems use spring loaded valve which are not known to provide very precise pressure control. 
     Accordingly, there remains a need for precise mechanical pressure control valves. 
     BRIEF SUMMARY OF THE INVENTION 
     This need is addressed by a mechanical valve incorporating a valve element and a sealing ring. 
     According to one aspect of the technology described herein, a valve includes: a housing defining a chamber communicating with an inlet port and an exhaust port, a seat disposed in the housing between the inlet port and the exhaust port; an elastomeric or polymer sealing ring disposed in the seat; a valve element having a sealing surface that is a body of revolution, the valve element positioned in the housing such that it is moveable between a closed position in which the sealing surface is engaged with the sealing ring and an open position in which the sealing surface is disengaged from sealing ring; and at least one bypass channel defined in the chamber, arranged to communicate between the seat and the exhaust port when the valve element is in the open position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
         FIG.  1    is a schematic, partially-sectioned view of an exemplary mechanical valve; 
         FIG.  2    is an enlarged view of a portion of  FIG.  1   ; 
         FIG.  3    is a top plan view of a portion of the valve of  FIG.  1   , showing an interior surface thereof; 
         FIG.  4    is a schematic diagram showing a geometric relationship of the valve element and sealing ring of the valve of  FIG.  1   ; 
         FIG.  5    is a view showing an alternative configuration of a weight; 
         FIG.  6    is a schematic, partially-sectioned view of a valve with a alternative embodiment of a valve element; 
         FIG.  7    is a schematic, partially-sectioned view of a valve incorporating a spring adjustment; 
         FIG.  8    is a schematic diagram of a system incorporating a mechanical valve; 
         FIG.  9    is a schematic diagram of a system incorporating a mechanical valve; and 
         FIG.  10    is a chart showing test performance of a valve as described herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG.  1    illustrates an exemplary valve  10 . The basic components of the valve  10  are a housing  12 , a seat  14 , a sealing ring  16 , and a valve element  18 . 
     In the illustrated example, the housing  12  comprises a body  20  and a cap  22 . The body  20  includes an interior channel  24  in flow communication with an inlet port  26  and the seat  14 . The inlet port  26  may include a threaded surface  28 , such as a standard pipe thread form, e.g., NPT. The presence of the threaded surface  28  permits the body  20  to be coupled directly to a structure with complementary threads, such as a pipe or pipe fitting (not shown). The pipe thread form may be male or female. 
     The seat  14  may take the form of a counterbore, groove, or other annular structure suitable to receive and hold a sealing ring  16  as described in more detail below. As best seen in  FIG.  2   , the body  20  includes a conical transition channel  30  between the seat  14  and the inlet port  26 , to provide clearance for the valve element  18 . 
     An annular sealing ring  16  is received in the seat  14 . In the illustrated example, the sealing ring  16  is an O-ring with a circular cross-sectional shape. The dimensions and material of the sealing ring  16  may be selected in conjunction with the properties of the valve element  18  to provide desired sealing performance. These parameters are discussed in more detail below. 
     The cap  22  is connected to the body  20 , for example using the illustrated bolts  31  or other suitable fasteners. The body  20  may include a protruding boss  32  which is received in a complementary portion of the cap  22  to provide a seal. Optionally, additional seals such as gaskets or O-rings (not shown) may be provided between the cap  22  and the body  20 . 
     The cap  22  includes an interior surface  34  defining a chamber  36  which is in flow communication with an exhaust port  38  and the seat  14 . The exhaust port  38  may include a threaded surface  40 , such as a standard pipe thread form, e.g. NPT. The presence of the threaded surface  40  permits the cap  22  to be coupled directly to a structure with complementary threads, such as a pipe or pipe fitting (not shown). The thread form may be male or female. 
     The valve element  18  is disposed inside the chamber  36  such that it may move between a closed position engaged with the sealing ring  16 , blocking flow communication between the inlet port  26  and exhaust port  38 , and an open position disengaged from the sealing ring  16 , which permits flow between the inlet port  26  and the exhaust port  38 . 
     In the example of  FIG.  1   , the valve element  18  is a sphere. This shape is useful because even if it rotates in operation, any one sealing diameter will be uniform and circular. The dimensions and material of the valve element  18  may be selected in conjunction with the properties of the sealing ring  16  to provide desired sealing performance. These parameters are discussed in more detail below. 
     The interior surface  34  of the cap  22  is formed into an array of lands  42  and grooves  44  (see  FIG.  3   ). The minimum dimension between the lands  42  is selected to provide a close fit with the maximum diameter of the valve element  18 , such that the valve element  18  may move in a vertical direction between open and closed positions as described above, but is held in a concentric position relative to the sealing ring  16 . 
     The grooves  44  define open channels around the valve element  18 , also referred to herein as “bypass channels”. The purpose of the bypass channels is to allow gas to flow around the valve element  18  and to the exhaust port  38 . As described in more detail below, these channels facilitate keeping the valve element  18  centered, which will reduce hysteresis and instability in the valve  10 . 
     Careful selection of the physical parameters of the valve element  18  and the sealing ring  16  will result in good performance. In this context, good performance is defined as ability to maintain a pressure setpoint within a predetermined tolerance at both low and high flow rates. For example, the maximum flow rate may be on the order of 100 times the minimum flow rate. 
     The sealing ring  16  may be made from an elastomeric material such as natural rubber or synthetic rubber, or from a polymer. Combinations of materials may be used. For best performance, the hardness of the sealing ring  16  is balanced against rigidity. This allows for preferred sealing performance to minimize gas leaks without introducing hysteresis from ultra-soft sealing rings. It is noted that high leakage is undesirable, since typical end uses have a finite gas supply capacity. It will be understood that a harder sealing ring may result in less hysteresis and more consistent performance, while a softer sealing ring may result in better sealing (i.e., less leakage). For applications such as safety relief valves in which the valve setpoint pressure is substantially above an operating pressure of the system, a relatively hard material such as PTFE may be employed, having a hardness of around 50 Shore D. For other applications, a medium-soft durometer value, for example around 50 Shore A, may be used. 
     The valve element  18  has a material, diameter, and roundness selected to give good characteristics for sealing and where. Materials such as hard polymers or metals may be used. One suitable option is a highly spherical shape to provide uniformity to the sealing ring surface. This will ensure that as the sphere may be allowed to rotate, any one sealing diameter will be uniform and circular, improving low flow performance. In one example, the valve element  18  may be a metallic sphere having a maximum surface finish of 0.13 μm Ra, and a diameter tolerance of +/−0.025 mm (+/−0.001 in.) 
     The ratio of valve element diameter “D” to sealing ring diameter “SD” (see  FIG.  4   ) is important). Having the ratio D/SD larger results in less stable operation because there is less constant inlet-side pressure force on the valve element  18 , and more variable pressure on the valve element  18  based on the position of the valve element  18  relative to the sealing ring  16 , but with a larger sealing ring  16  (i.e., smaller ratio D/SD) there is more constant inlet-side gas pressure on the valve element  18 , and less unstable downstream pressure effects on the valve element  18  as the valve element  18  oscillates on the sealing ring  16 . So, stability favors relatively larger sealing rings. But, too large of a sealing ring  16  increases static friction (“stiction”) on the sealing ring  16  because the radial forces approach the static friction coefficient and the valve element  18  can grab (hysteresis). In one example, a preferred ratio of valve element diameter to sealing ring diameter D/SD may be about 1.32 to about 1.18. Selection of the sealing ring cross-section diameter “CS”, inside diameter “ID”, and valve element diameter “D” affect the ratio D/SD. Furthermore, since pressure acts normal to a surface, and the object generating the setpoint may be a nearly perfect sphere, the lateral (X-direction) components of the fluid pressure vector act to align the center of gravity of the spherical valve element  18  with the geometric center of the sealing ring, thereby providing high alignment. This is preferred since high alignment allows for optimal sealing (less gas wasted), and reduces frictional forces and wasteful effort generated from the valve element  18  rattling around in the housing  12 . 
     The desired relationship between valve element diameter D and sealing ring diameter SD may be expressed as a contact angle. The contact angle ( FIG.  4   ) may be measured as the angle A between a line which is mutually tangent to the contacting surfaces of the valve element  18  and the sealing ring  16 , and a line which is normal to a mutual central axis C of the valve element  18  and the sealing ring  16 . In one example, this contact angle A may be about 49 degrees to about 58 degrees. Selection of the sealing ring cross-section diameter “CS”, inside diameter “ID”, and valve element diameter “D” affect the contact angle A. 
     Optionally, a weight  46  ( FIG.  1   ) may be provided in the chamber  36  on top of the valve element  18 . This separate weight  46  is helpful to provide a means for adjustment, as the valve&#39;s setpoint can be changed by using different weights. Furthermore, the use of a separate valve element  18  and weight  46  may be useful in preventing oscillation (“chattering”) of the valve element  18  during operation. 
     In the example shown in  FIG.  1   , the weight  46  is generally cylindrical, with a planar end surface  48  contacting the valve element  18 . The weight  46  may be solid, solid with one or more recesses formed therein, or hollow. The outside diameter of the weight  46  may be selected to provide a close fit with the minimum dimension between the lands  42 , such that the weight  46  may freely move in a vertical direction but is held in a concentric position relative to the sealing ring  16 . 
     Alternatively, as seen in  FIG.  5   , a weight  146  could have a concave end surface  148  contacting the valve element  18 . This would provide for a greater mass within the overall combined outside dimensions of the valve element  18  and the weight  146 . 
       FIG.  6    shows an alternative valve element  118 . It has an elongated body  120  including a sealing surface  122  which is a body of revolution about central axis “C”, e.g. a conical, spherical, or elliptical shape. A hemispherical example is shown. The outside diameter of the valve element  118  may be selected to provide a close fit with the minimum dimension between the lands  42 , such that the valve element  118  may freely move in a vertical direction but is held in a concentric position relative to the sealing ring  16 . For best performance, the concentricity of the valve element  118  should be held to a tight tolerance. In one example, concentricity of the metal sealing surface may be +/−0.0254 mm (+/−0.001 in.) at the contact band with the sealing ring  16 . The sealing function of the valve using the elongated valve element  118  is substantially similar to the operation described above. 
     One method of operating the valve  10  is by gravity only. In this mode, the mass of the valve element  18  generates a setpoint force in the system as the only resisting force to fluid pressure. This is robust, since gravity is a reliable and repeatable way of setting a force balance within the system. The valve element  18  will only lift once the static pressure below the valve element  18 , which is defined by the tangential diameter of the defined ball diameter and sealing ring size. 
     For gravity operation, the axis C would be positioned vertical (i.e., plumb) to the Earth or nearly so, with the inlet port  26  on the bottom, and the exhaust port  38  on top. As noted above, the separate weight  46  is optional. 
     The channels in the housing  12  to allow relief gas to move through are important, since minimizing friction during this step is helpful to precision, which is useful when using the mechanical valve to replace precise electronic components. The lands ( FIG.  1   ) act to keep the valve element  18  in alignment with the geometric center of the sealing ring  16 , reducing hysteresis. The open channels around the valve element  18  are activated when the valve element  18  lifts off the sealing ring  16 . Additionally, the lands  42  limit the contact area on the valve element  18  from a ring (as would be the case in a sleeve geometry) to a few contact points, which reduces surface friction due to contact. This also reduces hysteresis, and increase accuracy of the valve  10 . The radial clearance between the valve element  18  and the lands  42  is an important parameter. Surprisingly, it has been found that less-than-perfect concentricity can improve the ability of the valve element  18  to reliably seat in the seal ring  16 . In one example, it has been found that a radial clearance “T” ( FIG.  2   ) of approximately 1.5% to 3% of the valve element diameter D results in good performance. This provides a small amount of room for lateral oscillations which are actually helpful to the dynamic flow performance curve, while keeping the valve element  18  adequately centered relative to the sealing ring  16 . 
     Another method of operating the valve  10  is by gravity in combination with spring forces.  FIG.  7    illustrates a variation in which the valve  10  is provided with a spring. A compression-type spring  50  is disposed above the valve element  18 . The lower end of the spring  50  contacts the valve element  18  (or weight  46  if used) and the upper end of the spring  50  contacts an adjuster assembly comprising a pressure plate  52 , adjustment screw  54 , and adjustment knob  56 . Turning the adjustment screw  54  inwards (downward in the figure) to a desired degree preloads the spring  50  which in turn applies a corresponding load to the valve element  18 . Stated another way, the adjuster assembly is operable to apply a variable preload to the spring  50 . The addition of the compressible spring  50  will allow for additional forces to resist fluid pressure. The presence of a spring provides the following benefits: 
     Adjustability through changes in compression to the spring, which changes the applied resistive force; 
     A convenient and immediate way of adjusting pressure setpoints; 
     Inertial mass dampening to dampen out ball vibration and “bouncing”, which reduces instability in high flow conditions; and 
     Additional downward force for re-alignment on the sealing ring. 
     The key to the optimal performance for this system is to select the proper spring constant to mass ratio. A preferred configuration for low-pressure control is to have a ratio in which the majority of the point load force is attributed to gravity, and the spring is slightly compressed to provide inertial mass dampening. The stronger the spring force is in the force balance equation, the steeper the pressure versus flow curve will be in the valve. This logic best applies to pilot valves and adjustable check valves/pressure reducing valves, where the low setpoint is almost entirely a result of the weight applied, and the spring to weight ratio largely stays less than 1 for the maximum setpoint. 
     Inertial dampening springs are helpful in safety relief devices, where the main objective is to relive pressure reliably without significant adjustment to prevent damage to the downstream process. 
     The various valve embodiments described above may be employed effectively for different purposes and various end applications. 
     For example,  FIG.  8    depicts schematically a process  200  requiring a regulated gas pressure. Gas pressure is supplied from a gas source  202  such as a pump or storage cylinder. The operating pressure supplied to the process  200  may be regulated by a back pressure regulator  204 , for example a diaphragm-type dome-loaded valve. 
     In one example, a mechanical valve  10  of the type described herein may be used as a overpressure relief valve or safety valve, item  206 , coupled between the gas supply  202  and the process  200 . The objective of a safety relief device is to reliably protect against overpressurization, which has the potential to damage the process  200 . The valve  206  is a simple device that minimizes the number of moving parts. In this application, the gravity-only configuration may be preferred. As one example, this type of valve may be used in applications requiring a setpoint from 55 to 103 mbar. 
     In another example, a mechanical valve of the type described herein may be used as a pilot valve  208  coupled between the gas supply  202  and the back pressure regulator  204  to reliably send a pneumatic signal to the back pressure regulator  204 . The mechanical valve  10  described herein is robust to supply pressure changes, and reliably relieves near the desired setpoint. As one example, this type of valve may be used in applications requiring setpoints in ranges of 5-25 mbar or 40-70 mbar. 
       FIG.  9    depicts schematically first and second processes  300 ,  302  each requiring a regulated gas pressure. Gas pressure is supplied from a gas source  304  such as a pump or storage cylinder. This figure only shows two processes, but theoretically an indefinite amount of processes can be supported as long as there is capacity from the gas source  304  to supply appropriately all processes with enough volumetric flow. The operating pressure supplied to each process  300 ,  302  is regulated by mechanical valves of the type described above, items  306 ,  308 , coupled between the gas supply  304  and the respective processes  300 ,  302   
     In this application, each valve  300 ,  302  may act as a differential pressure valve. As described earlier, the valve element in this system only moves if the net static fluid pressure is greater than the downward gravity force. Thus, there is a minimum point load force required, which can be then translated to a static fluid pressure. In the schematic above, the downstream pressure will be non-zero, but will always be less than the supply pressure P_supply. Thus, this device will open when the subtraction of P_supply−P2 (p2=downstream pressure), and thus the same requirement for the differential to exceed the gravity force must be met for flow to resume or cease. This will then mean that by carefully selecting the right diameter and density of the valve element setpoint, differential pressure check control is achievable. 
     As one example, this type of valve may be used in applications requiring setpoints in a range of range of 5-70 mbar. 
     The valves as described herein exhibit extremely good precision compared to prior art valves. As an example,  FIG.  10    illustrates the performance of the valve  10  tested in a gas system with a pressure setpoint of 60 mbar. It can be seen that the valve  10  is capable of maintaining system pressure within plus or minus 10% of the setpoint overflows from 0.05 L per minute to 5 L per minute, or a flow range of 100:1. Such performance is not seen in prior art valves. 
     The foregoing has described a valve. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
     Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     The invention is not restricted to the details of the foregoing embodiment(s). The invention extends any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.