Abstract:
A valve with a calibrated flow orifice insert for use in Heating, Ventilation, and Air Conditioning (“HVAC”) applications so as to provide metered flow through the valve. The insert is used as a flow control device and is inserted into a conventional threaded ball valve. The insert has a cylindrical axial bore that is sized to provide a maximum valve flow coefficient. Peripheral threads on the insert mate with interior threads on the inlet of the valve body. A pair of bores on the face of the insert permit threaded insertion into the valve. The axial orifice bore through the insert is sized using experimentally-determined formulas related to the Reynolds numbers for the orifice and for the piping upstream of the insert.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a non-provisional counterpart of pending U.S. Provisional Patent Application No. 60/352,439, filed Jan. 28, 2002, fully included by reference herein, and claims priority benefit thereof. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         REFERENCE TO COMPACT DISC(S)  
         [0003]    Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention  
           [0005]    The present invention relates, in general, to valves used in the commercial heating, refrigeration, and air conditioning industry, and in particular, to valves for precisely metering the flow of fluid therethrough.  
           [0006]    2. Information Disclosure Statement  
           [0007]    It is often desired to achieve constant flow control when dealing with a fluid used in any Heating, Ventilation &amp; Air Conditioning (“HVAC”) application. Well-known solutions for this problem include the use of linear globe valves. A linear globe valve uses a multi-turn handwheel that operates a linear rising-stem control element, which closes onto a seating surface. A complex flow path through the valve, along with the linear rising-stem, allows the globe valve to possess important key features. One key feature is the high level of precision when throttling. Another key feature is the inherent rangeability, which is defined as the ratio of the maximum flow to the minimum controllable flow through the valve passage. Also, the inherent flow characteristics of the linear globe valve allows it to exhibit “equal percentage flow,” i e., an inherent flow characteristic which, for equal increments of rated travel, will ideally yield equal percentage changes of the existing flow.  
           [0008]    Unfortunately, some inherent disadvantages still remain with the linear globe valve design. One disadvantage with this type of valve is that it contains a contoured plug that works in conjunction with a metal seat. When the plug is pressed against the metal seat, there is no sealing surface to close against; thus there is wasted energy, or in this case leakage. Other recognized disadvantages with the linear globe valve design include a high pressure drop across the valve due to a restricted flow passage when the valve is fully open, and the need for a sufficient amount of space in order to open the valve, because it is controlled by a rising-stem. These undesirable factors must be taken into consideration when using this valve in any piping system.  
           [0009]    In order to maintain all of the admirable performance characteristics of the linear globe valve without having to deal with considerably high-pressure losses, modified ball valves may be used in place of globe valves. FIG. 1 shows such a typical well-known conventional ball valve  20  having a threaded inlet port  22  and outlet port  24 , each port having internal threads  26  of standard pitch and size for receiving similarly-threaded pipes (not shown) therewithin in a manner well-known to those skilled in the art. FIG. 9 shows another typical well-known conventional ball valve  2 . 20  having non-threaded inlet and outlet ports 2.22, 2.24 into which inlet and outlet pipes P are soldered in a manner well-known to those skilled in the art. Other than the threaded/non-threaded aspect of the ports, the prior art valves of FIGS. 1 and 9 are otherwise substantially the same, and a description of the valve of FIG. 1 will suffice for both, it being understood that similar structural features perform similar functions for both types of valves.  
           [0010]    Well-known ball valve  20  includes a valve body  28 , usually of a metal such as brass or stainless steel, a generally spherical ball  30 , typically of a metal such as brass or chrome or stainless steel and having a transverse cylindrical bore  32  therethrough. Ball  30  is mounted for rotation with a metal stem  34 , typically brass or stainless steel, about a vertical axis of stem  34  such that a 90° rotation of stem  34  about its axis causes ball valve  20  to go from a fully-closed position (shown in dotted outline) in which the cylindrical bore  32  of ball  30  is transverse to the axis of input and output ports  22 ,  24 , to a fully-open position (shown in solid outline) in which the cylindrical bore  32  is aligned with the axis of input and output ports  22 ,  24 . Stem  34  is typically mounted in a polytetrafluoroethylene (“PTFE”) polymer (often sold under the trademark TEFLON) stem bearing  36  within Namur mount  40  of like metal as valve body  28  for rotation of stem  34  with respect to valve body  28 , and stem  34  may be sealed with a PTFE polymer stem seal  38  and one or more Viton O-rings  42 . Typically, a well-known electrically-operated actuator (not shown) is coupled to stem  34  so as to cause the ball valve  20  to cycle between its open and closed positions in a manner well-known to those skilled in the art.  
           [0011]    Pressure losses across these valves are small compared to those in globe valves. They exhibit excellent performance for on/off service, and the amount of shut-off leakage around the spherical control element of the ball valve is minimal, which allows for positive shut-off. Positive shut-off is referred to by the American National Standards Institute as a Class VI, “bubble tight” situation, which means that when the valve was tested under laboratory conditions with compressed air, no leakage was observed. Standard ball valves possess many excellent features, but do not exhibit desirable flow control. The advantage of using modified ball valves over the traditional style linear globe valves includes similar flow characteristics while making quarter-turn automation simple and economical.  
           [0012]    Several different modified ball valves have been introduced to the valve industry in the last few years. A ball valve that uses a polymer insert to achieve equal percent flow characteristics is sold under the trademark OPTIMIZER by Griswold Controls, Inc., 2803 Barranca Pkwy, Irvine, Calif., and is described in a Griswold brochure entitled “HVAC Technology Review—Griswold Controls Introduces Optimized Temperature Control,” and in Mirandi, U.S. Pat. No. 5,937,890 (issued Aug. 17, 1999), fully included herein by reference. The Griswold OPTIMIZER ball valve insert is an insert that is press-fit into the spherical control element. It allows for multiple valve flow coefficient (C v ) selection for the user. The OPTIMIZER ball valve insert is designed for use in the manufacturer&#39;s valve only. Temperatures and pressures in the system must be limited due to the fact that the insert is made of a polymer material and could fail under certain conditions. Because of this problem, steam can not be used as the working fluid in the system. Fouling can also be a problem with the discs designed to yield smaller valve flow coefficient (C v ) values. With the narrow design of the parabolic shape of the orifice, small pieces of debris within the system could get trapped, disrupting the flow through the orifice and minimizing control. Due to the press fit design, the insert could become loose and potentially removed under high pressure.  
           [0013]    Other attempts to address the poor control of a standard ball valve are ball valves with a disk insert sold under the trademark “Characterized Control Valves” and manufactured by Belimo Aircontrols (USA) Inc., 43 Old Ridgebury Road, Danbury, Conn. The disk insert is made of polytetrafluoroethylene (“PTFE”) polymer material, such as that sold under the trademark TEFLON, and is placed in the valve body upstream of the control element. The disk insert is held in place by the use of a retaining ring. Like the Optimizer, this control device can only be used in the manufacturer&#39;s valve. As with the Optimizer design, the PTFE insert could fail under high pressures and temperatures, the smaller parabolic orifice passages could become obstructed, and the insert could become loose and possibly removed under high pressure because of the simple retaining ring used to hold the insert in position. These Characterized Control Valves are described in a Belimo Aircontrols brochure entitled “The Difference is in the Details” and also are described in Carlson et al., U.S. Pat. No. 6,039,304 (issued Mar. 21, 2000), fully included herein by reference.  
           [0014]    A ball valve that uses a one-piece lubricant-impregnated metal seat and is configured to provide a concave central surface portion that makes full-face direct sealing contact with the ball is sold by Worcester Controls Corporation, Marlboro, Mass., and is described in Reynolds et al., U.S. Pat. No. 5,074,522 (issued Dec. 24, 1991), fully included herein by reference. This design improves the flow control of a standard ball valve, but is an expensive alternative when compared with other designs in the industry. The Worcester valve is designed specifically for high pressure industrial applications, and is limited in regards to maximum C v  due to the specified geometry of the designed metal seats. When dealing with high pressure situations, the ball valve design must include very tight direct sealing contact between the spherical control element and the seats that are located adjacent the upstream and downstream sides of the valve within the valve housing. Due to the tight seal between the control element and the seats, the torque that is necessary to rotate the control element is greater than that found in a modified ball valve used in HVAC applications. In order to use automation to control the Worcester valve, expensive actuators would have to be used that have high torque capabilities. Fouling can also be a problem when a metal seat is used containing several small holes to regulate the flow. Debris can block several of the holes, changing the characteristics of the design, and limiting flow control  
           [0015]    It is therefore desirable to have a flow control device that is intended to obviate problems of the types discussed above with respect to the Griswold, Belimo, and Worcester valve arrangement.  
           [0016]    In addition to the Griswold Controls, the Belimo Aircontrols, and the Worcester Controls Corporation references mentioned above, the inventor also is aware of the following patent references, some of which may be relevant to the present invention: Wiley, U.S. Patent No. 1,493,409, issued May 6, 1924; Hodgeman et al., U.S. Pat. No. 3,126,917, issued Mar. 31, 1964; Baumann, U.S. Pat. No. 4,085,774, issued Apr. 25, 1978; Ko, U.S. Pat. No. 4,903,725, issued Feb. 27, 1990; McEnearney, U.S. Pat. No. 4,960,260, issued Oct. 2, 1990; Yu, U.S. Pat. No. 5,123,628, issued Jun. 23, 1992; Schommer, U.S. Pat. No. 5,315,859, issued May 31, 2994; Gawlik, U.S. Pat. No. 5,655,571, issued Aug. 12, 1997; Sharp, U.S. Pat. No. 5,687,770, issued Nov. 18, 1997; and Lebo et al., U.S. Pat. No. 5,819,803, issued Oct. 13, 1998.  
           [0017]    None of these references, either singly or in combination, are believed to disclose or suggest the present invention.  
         BRIEF SUMMARY OF THE INVENTION  
         [0018]    The present invention is an insert that is used as a flow control device and can be retrofitted into any conventional threaded ball valves. The insert includes a concentric orifice that can be formed to different sizes to provide the desired maximum valve flow coefficient, or C v . The orifice insert consists of standard National Pipe Taper (“NPT”) threads, which are sized to mate with a predetermined valve size. When installed into the valve body, the external straight threads on the insert interlock with the tapered threads within the valve body creating a secure locking mechanism. This method of installation will prevent the insert from becoming loose and possibly removed when encountered by high pressures and temperatures. The orifice insert may be machined from brass, carbon steel, stainless steel and other alloys, depending upon the particular application. These materials are able to withstand rather high pressures and temperatures without failing, which enables the flow control device to be used for steam applications. The axial concentric orifice design allows a conventional ball valve to become an excellent control valve. The designed orifice insert allows the ball valve to exhibit true “equal percentage flow characteristics” over the entire 90° rotation, and the rangeability of the valve is greatly improved. Fouling is almost eliminated with the centrally disposed single orifice machined in each insert. The present design does not require very tight direct sealing contact between the spherical control element and the PTFE seats that are located adjacent the upstream and downstream sides of the ball valve within the valve housing. This makes quarter-turn automation simple and economical because the need for high-torque actuators is eliminated. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0019]    [0019]FIG. 1 is a longitudinal side sectional view of a conventional well-known ball valve having threaded inlet and outlet ports.  
         [0020]    [0020]FIG. 2 is a longitudinal side sectional view of the prior art ball valve of FIG. 1 into which the calibrated flow orifice insert of the present invention has been fitted.  
         [0021]    [0021]FIG. 3 is an end view of the calibrated flow orifice insert of the present invention.  
         [0022]    [0022]FIG. 4 is a longitudinal sectional view of the calibrated flow orifice insert of the present invention, taken substantially along the line  4 - 4  shown in FIG. 3.  
         [0023]    [0023]FIG. 5 is a perspective view of the calibrated flow orifice insert of the present invention.  
         [0024]    [0024]FIGS. 6, 7, and  8  are graphs of the Reynolds number through the orifice (“Re do ”) versus the Reynolds number through the upstream piping (“Re Di ”) for various sizes of pipe.  
         [0025]    [0025]FIG. 9 is a longitudinal side sectional view of a conventional well-known ball valve having non-threaded inlet and outlet ports into which inlet and outlet pipes are soldered.  
         [0026]    [0026]FIG. 10 is a longitudinal side sectional view of the prior art ball valve of FIG. 9 into which a second embodiment of the calibrated flow orifice insert of the present invention has been fitted.  
         [0027]    [0027]FIG. 11 is an end view of the second embodiment of the calibrated flow orifice insert of the present invention.  
         [0028]    [0028]FIG. 12 is a longitudinal sectional view of the second embodiment of the calibrated flow orifice insert of the present invention, taken substantially along the line  12 - 12  shown in FIG. 11.  
         [0029]    [0029]FIG. 13 is a perspective view of the second embodiment of the calibrated flow orifice insert of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    Referring to FIGS. 1 through 5 and  9  through  13 , the present invention provides a flow control device, such as insert  50  and  2 . 50 , which may easily be retrofitted into conventional prior art threaded ball valves  20  and unthreaded ball valves  2 . 20 , upstream of the spherical control element or ball  30 ,  2 . 30  by securing with either a retaining ring, press fitting, gluing, soldering, or threading. As explained hereinabove, prior art ball valve  20  shown in FIG. 1 is substantially the same as prior art ball valve  2 . 20  shown in FIG. 9, the only difference being that well-known ball valve  20  has internally-threaded inlet and outlet ports  22 ,  24  for threadedly receiving similarly-threaded pipes (not shown) therewithin, whereas well-known ball valve  2 . 20  has non-threaded inlet and outlet ports  2 . 22 ,  2 . 24  into which non-threaded pipes P are soldered in a manner well-known to those skilled in the art. Other than the threaded/non-threaded aspect of the ports, the prior art valves of FIGS. 1 and 9 are otherwise substantially the same, and a description of the valve of FIG. 1 will suffice for both, it being understood that similar structural features perform similar functions for both types of valves. For clarity, similar structural features of ball valve  2 . 20  are given the same reference numerals as those of ball valve  20  except with a prefix “ 2 .”. Likewise, the first embodiment insert  50  of the present invention, for use with threaded ball valve  20 , has many structural features that are similar to those of the second embodiment insert  2 . 50  of the present invention, which is for use with the non-threaded ball valve  2 . 20 . Again, for clarity, similar structural features of insert  2 . 50  are given the same reference numerals as those of insert  50  except with a prefix “ 2 .” and a description of insert  50  will suffice for the common structural features of both, with differences between the two embodiments being discussed hereinafter.  
         [0031]    Orifice inserts  50  are substantially cylindrically symmetric and have a disk-like flange  58  that is circumferentially threaded with well-known and standard NPT threads  52  that are sized to mate with the internal inlet port threads  26  for a predetermined valve size, which may typically vary from one-half inch to two inches (1.3 to 5.1 cm) in inner diameter. There are two alignment/insertion/removal holes  54  on the face of flange  58  of orifice insert  50  to allow for easy threadable installation into the valve  20 . The orifice inserts  50 , having external straight threads  52  disposed about the periphery thereof interlock with the tapered threads  26  within the valve body  28  creating a secure locking mechanism. A centrally disposed and axially-aligned orifice or bore  56  is formed in the flow control device insert  50  to provide the desired valve flow coefficient, or C v . The orifice  56  may be sized to meet specific flow control requirements and eliminates the need for multiple pipe reducers to achieve the same results. The orifice  56  acts as a fixed mechanical flow limiter that allows only the new desired flow to exit the ball valve  20  no matter what the previous maximum valve flow coefficient C v  the manufacturer has incorporated into the design of the valve  20 . As the diameter of the orifice  56  is selected to be larger or smaller, a desired maximum valve flow coefficient C v  can be achieved. The outcome of the combination of a standard ball valve  20  and the insert  50  of the present invention is a valve that has an infinite range of valve flow coefficients (C v ) that are lower than the valve&#39;s maximum rated flow coefficient (C v ), depending on the diameter of orifice  56  that is selected for the insert  50 . This gives the operator the ability to obtain the control that is necessary in the HVAC industry. There is an elongated cylindrical rear section  60  that extends rearwardly from orifice insert  50 . When the flow control device insert  50  is placed within the valve body  28 , the rear end of the elongated section  60  aligns with the PTFE polymer seat  44  to form a passage that directs the flow into the spherical control element  30 . Note however, as seen best in FIG. 2, that the rear face  62  of elongated rear section  60  must not extend too far rearwardly because otherwise it might contact ball  30  when the ball  30  is rotated so as to close the valve, as shown in dotted outline. It has been found that the small gap or chamber  64  between the rear face of insert  50  and ball  30  when the valve is in the opened position does not substantially impair the performance of the valve. The orifice insert  50  may be machined from brass, carbon steel, stainless steel and other alloys, depending upon the particular application.  
         [0032]    After testing different size orifice inserts under controlled laboratory conditions, the valve coefficients can be determined using the experimental results of this testing. Once the valve coefficient (C v ) values have been determined, the Reynolds number for each specimen can be calculated and graphed. The graphs of FIGS. 6, 7, and  8  were developed with the Reynolds number through the orifice insert (“Re do ”) on the vertical axis, and the Reynolds number through the upstream piping (“Re Di ”) on the horizontal axis. With the graphs constructed, a polynomial trend line was used to fit all of the data points plotted within each graph and to determine the coefficients of a third-order equation that best fits the experimental data for various sizes of ball valve inner diameters. Using polynomial equations to calculate the orifice diameter for the 0.5 to 2.0 inches (1.3 to 1.5 cm) valve sizes, the maximum error encountered was 7.1%, with an average error of 2%. The generalized third-order “best fit” polynomial for each graph is of the form:  
           Re   do   =K   3 ( Re   Di ) 3   +K   2 ( Re   Di ) 2   +K   1 ( Re   Di ) 1   +K   0    
         [0033]    The correct sizing of the orifice  56  in the flow control device insert  50  can then be found using this best-fit third-order equation for the experimental data for the particular size of ball valve inner diameter, where Re do  is the Reynolds number through the orifice and Re Di  is the Reynolds number through the upstream piping.  
         [0034]    For ball valve inner diameters between about 0.5 to 0.75 inches (1.3 to 1.9 cm) inclusive, whose graph is shown in FIG. 6, the polynomial coefficients for the best-fit third-order equation are determined to be:  
           K   3 =4×10 −11   , K   2 =−1×10 −5 ,  
         K 1 =1.756, K 0 =9687.80  
         [0035]    such that  
         Re   do     =       4   ×     10     -   11              (     Re   Di     )     3       -     1   ×     10     -   5              (     Re   Di     )     2       +     1.756        (     Re   Di     )       +   9687.80                           
 
         [0036]    For a ball valve inner diameter of substantially 1.0 inch (2.5 cm), whose graph is shown in FIG. 7, the polynomial coefficients for the best-fit third-order equation are determined to be:  
         K 3 =0,  K   2 =−2×10 −6 , K 1 =1.32, K 0 =18983  
         [0037]    such that  
           Re   do =−2×10 −6 ( Re   Di ) 2 +1.32( Re   Di )+18983  
         [0038]    For a ball valve inner diameter of 1.25, 1.5 and 2.0 inches (3.2, 3.8 and 5.1 cm) and thus between about 1.25 to 2.0 inches (3.2 to 5.1 cm) inclusive, whose graph is shown in FIG. 8, the polynomial coefficients for the best-fit third-order equation are determined to be:  
           K   3 =3×10 −12   , K   2 =−3×10 −6 ,  
         K 1 =1.51, K 0 =21643  
         [0039]    such that  
         Re   do     =       3   ×     10     -   12              (     Re   Di     )     3       -     3   ×     10     -   6              (     Re   Di     )     2       +     1.51        (     Re   Di     )       +   21643                           
 
         [0040]    The Reynolds number is a dimensionless ratio of inertia forces to viscous forces in the flow. It is a widely accepted and easily recognized ratio that is commonly used in fluid mechanics.  
         [0041]    The Reynolds number can be calculated for the flow through the orifice using the following equation:  
         Re   do     =       4      Q       π                   d   o        v                             
 
         [0042]    Where:  
         [0043]    Q=volume flow rate through orifice  
         [0044]    d o =diameter of orifice in insert  
         [0045]    v=kinematic viscosity of fluid term  
         [0046]    The Reynolds number can be calculated for the flow through the upstream piping using the following equation:  
         Re   Di     =       4      Q       π                   D   i        v                             
 
         [0047]    Where:  
         [0048]    Q=volume flow rate through upstream piping  
         [0049]    D i =actual inside diameter of pipe  
         [0050]    v=kinematic viscosity of fluid term  
         [0051]    For example, a piping system is made of 0.5 inch (1.3 cm) schedule 80 polyvinyl chloride (“PVC”). A 0.5 inch (1.3 cm) ball valve is used to regulate the flow of water through the system. If a valve coefficient (C v ) value of 10.4 is desired, what size orifice should be machined in the insert that is placed upstream of the spherical control element? 
         [0052]    The Reynolds number through the upstream piping (Re Di ) can be calculated by using the equation:  
         Re   Di     =       4        (     40.04          in   3     s       )           π        (     0.546                 in     )              (     0.00135          in   2     s       )                                         
 
         [0053]    Where:  
         [0054]    Q=volume flow rate through upstream piping:  
         [0055]    C v =10.4=10.4 gpm=40.04 in 3 /s  
         [0056]    When water is used for the fluid, the volume flow rate is equal to the valve coefficient from the equation:  
         C   v     =     Q       Δ                 p                               
 
         [0057]    Where:  
         [0058]    C v =valve coefficient  
         [0059]    Q=volume flow rate  
         [0060]    Δp=pressure drop through valve passage  
         [0061]    By definition, the valve coefficient is the number of U.S gallons per minute that will pass through a valve passage with a pressure drop of one PSI. Using reference texts:  
         [0062]    D i =actual inside diameter of 0.5 inch (1.3 cm) schedule 80 pipe:  
         [0063]    =0.546 inches (1.387 cm)  
         [0064]    v=kinematic viscosity of fluid term:  
         [0065]    =0.00135 in 2 /s (0.0087 cm 2 /s)@ 80° F.  
         [0066]    Performing the calculation above yields:  
         Re Di =69,200  
         [0067]    The third-order polynomial equation can now be used to calculate the Reynolds number through the orifice insert (Re do ):  
           Re   do     =       4   ×     10     -   11              (     69   ,   200     )     3       -     1   ×     10     -   5              (     69   ,   200     )     2       +     1.756        (     69   ,   200     )       +   9687.80                                        
 
         [0068]    or,  
         Re Do =86,987  
         [0069]    Substituting into the equation for the Reynolds number through the orifice insert (Re do ) yields:  
         86   ,   987     =       4        (       40.04                    in   3     s       )           π        (     d   o     )            (     0.00135          in   2     s       )                               
 
         [0070]    Rearranging and solving for the orifice diameter gives:  
         d   o     =         4      Q       π                   Re   do        v       =       4        (     40.04          in   3     s       )           π        (     86   ,   987     )            (     0.00135          in   2     s       )                                 
 
         [0071]    or,  
         d o =0.434 inches (1.102 cm)  
         [0072]    Thus, an insert with an orifice diameter of 0.434 inches (1.102 cm) will provide the user with the desired valve coefficient C v  of about 10.4.  
         [0073]    [0073]FIGS. 9 through 13 show the use of a second embodiment  2 . 50  of the ball valve insert of the present invention being used with a non-threaded ball valve  2 . 20 . This second embodiment  2 . 50  is substantially the same as the first embodiment  50  except that the second embodiment  2 . 50  does not have circumferential threads  52  around flange  58 , and second embodiment  2 . 50 , being unthreaded, does not require alignment/insertion/removal holes (corresponding to holes  54  of insert  50 ) in the face of flange  2 . 58 . Insert  2 . 50  is placed within the inlet  2 . 22  of valve  2 . 20  and is soldered into the valve body. After the insert  2 . 50  has been soldered into the valve body, the pipes P are then soldered into the inlet and outlet ports in the usual manner. Again note however, as seen best in FIG. 10, that the rear face  2 . 62  of elongated rear section  2 . 60  must not extend too far rearwardly because otherwise it might contact ball  2 . 30  when the ball  2 . 30  is rotated so as to close the valve, as shown in dotted outline. It has been found that the small gap or chamber  2 . 64  between the rear face of insert  2 . 50  and ball  2 . 30  when the valve is in the opened position does not substantially impair the performance of the valve.  
         [0074]    The metal construction of inserts  50  and  2 . 50  permits the inserts to be used in harsh temperatures and pressures, as is often encountered when steam is flowing through ball valves. Furthermore, the rigid securing by threads  52  or soldering of the insert into the valve body, and the metal construction of the insert, produces a structure that is substantially “blow out proof”.  
         [0075]    It has been found that the inserts of the present invention, while preferably being located in the inlet or upstream port, can be used bi-directionally (i.e., in either the inlet or the outlet ports of the ball valve) with only slightly different resulting C v  when the insert is used in the downstream or outlet port of the valve.  
         [0076]    An important feature of the inserts of the present invention is that, unlike prior art inserts, they are readily usable in standard ball valves because of the threaded securing into the ball valve (or the soldered securing, as appropriate for non-threaded ball valves), and do not require specially-made ball valves for their use. Because of this feature, the inserts are “field retrofittable” and can be retrofitted into an already-installed system without having to replace the valve. For example, as an HVAC system ages, the flow characteristics of the piping change because of corrosion or deposit buildup, etc., within the piping. The present invention can be simply and easily used to modify the C v  of an aging HVAC system by exchanging one insert, having a first selected diameter for bore  56  (or  2 . 56 , as appropriate) with a different insert, having a different selected bore diameter, thereby changing the C v  of the system to a modified value in accordance with the equations discussed hereinabove. As another example, a HVAC system could be modified after installation to have a desired C v  simply by choosing one of a set of inserts  50  (or  2 . 50 , as appropriate), where the set of inserts has a range of bore diameters that allow a range of C v  to be specified. This flexibility permits a given valve size to have a multiple number of possible C v  settings lower than the maximum valve capacity, simply by changing the insert.  
         [0077]    Although the present invention has been described and illustrated with respect to a preferred embodiment and a preferred use therefor, it is not to be so limited since modifications and changes can be made therein which are within the full intended scope of the invention.