Abstract:
A live-loading assembly for exerting a sealing force on a compressible packing structure of a fluid handling device, such as a valve or pump, includes a pair of gland bolts each movably extending through opposite end lids of a tubular cartridge and through a Belleville spring stack disposed within the cartridge and bearing on a tubular piston rod having an end portion extending outwardly through one of the lids and having a spring force indicating scale disposed thereon. When packing force adjustment nuts are tightened onto the bolts, to increase the compression force exerted on the packing structures, one of the lids on each cartridge moves along the associated exposed piston rod scale to thereby provide a visual indication of the amount of spring force being created by each tightened nut.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of the filing date of provisional U.S. patent application No. 61/825,272 filed May 20, 2013. The entire disclosure of the provisional application is hereby incorporated herein by this reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to apparatus for live-loading a valve or other fluid handling device packing that indicates the actual force being exerted on the packing. The apparatus can also indicate the operational ranges for different packing sets the apparatus is designed to work with. More particularly, the present invention relates to a dynamic actuator that compresses during packing expansion and expands when the packing relaxes, indicating at all times the actual force being exerted on the packing. 
       BACKGROUND 
       [0003]    Mechanical equipment used in the handling of liquids or gases may be subject to leakage problems, for example, valve stems, shafts or rods. The successful use of such equipment to contain and handle liquids or gases requires adequate control of this leakage, and several sealing methods and devices have been used to achieve such leakage control. 
         [0004]    Compression packing is one of the most common devices used in sealing, and is used in many industries, including chemical, pharmaceutical, marine, sewage, and others. Compression packing involves the insertion of the packing made from soft, pliant materials into the space (i.e., the stuffing box) between a rotating or reciprocating member of a pump or valve and the body of the pump or valve. When pressure is transmitted to the packing materials, the materials expand against the stuffing box and the valve or pump member, thereby creating a seal. Compression may be applied to packing by means of packing bolts which are attached at one end to a clamp around the valve body and at the other end to a spigot, a flange or other projection bearing on, integral with or attached to the gland or sleeve which bears against the packing. Tightening of the packing bolts, therefore, increases the pressure on the packing and thereby exerts the radial pressure on the stem and the stuffing box. The resulting radial pressure of the packing onto the stem and stuffing box provides the desired seal so long as the radial pressure exceeds the pressure of fluid in the valve. 
         [0005]    Improper loading is a condition wherein the sealing compression exerted by the gland follower on the packing is either insufficient or excessive. Packing volume variations and bolt creep are contributing elements of improper loading, because both will induce changes in the compressive force applied by the gland follower on the packing. But inaccurate torquing of the gland bolts by workers may also cause improper loading. Such inaccurate torquing may be the result of human errors. However it is recognized that even when torque wrenches are used by workers they are often inaccurate, resulting in improper loading. Leaks thus occur from the outset because the load on the packing is insufficient to achieve or maintain a seal, or excessive to damage the packing. Fluid leakage along the shaft of valves and pumps has long been recognized as a serious problem in power and industrial plants. In recognition of this problem, various attempts have been made to obtain leak free performance and reduce maintenance requirements for a pump or a valve. For example, improved packing materials have been developed for a larger range of temperatures, better chemical resistance and improved coefficient of expansion characteristics. Torque values have been established for the bolts connecting the gland follower to the stuffing box. Installers follow such specifications to apply a proper load to the packing to achieve a seal, but as discussed above may not attain a proper load. Several companies have initiated routine maintenance programs that include re-torquing of gland follower bolts. Such re-torquing is done frequently because of the significant risk posed by improperly loaded gland bolts and the resulting leakage of fluid from the apparatus. 
         [0006]    Another attempt to obtain leak free performance and reduce maintenance requirements involves live-loading of the gland follower. Live-loading (or “dynamic loading”) refers to the mounting of compressed springs on the gland follower whereby a continuous force is exerted on the gland follower to insure a regular compressive pressure is exerted on the packing. Although coil springs could be used, it is conventional practice to use so-called Belleville springs which are essentially formed as a stacked series of dished washers that flatten when compressed. A significant amount of force is required for this compression. Such springs have higher compression rating than simple coil springs. 
         [0007]    The use of Belleville springs provides a live-load system which can continuously compensate for changes that may take place in the packing under operating conditions of the valve, for example high pressures and temperatures. Polytetrafluoroethylene (PTFE) packings for instance, are very susceptible to undergo volume changes when exposed to temperature variations since the thermal expansion coefficient of PTFE is nearly ten times greater than that of steel. In such cases, the volume of the material may reduce under operating conditions and, whereas this could harmfully affect the sealing in an unsprung valve, the spring force will compensate for this reduction and maintain the packing under pressure. Alternatively, if the packing volume increases, the pressure on the stem, gland follower and stuffing box in an unsprung valve could increase too much and possibly cause sticking of the stem, extrusion of the packing or both. The live-loaded valve however can accommodate the pressure increase by means of further compression of the springs. 
         [0008]    Thus, the live-loaded packing construction can provide a useful amount of self-adjustment, but the exact amount of force actually being exerted on the packing typically remains unknown. Accordingly, it is very difficult to precisely determine if the correct load is actually being applied to the compressible packing material. 
         [0009]    Therefore, a need exists to provide an improved dynamically-loaded packing system that not only supplies the amount of self-adjustment necessary to maintain adequate pressure on the packing, but also indicates the force being exerted on the packing at all times to thereby prevent improper loading of the packing system. It is to this need that the present invention is primarily directed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a partially cross-sectioned diagrammatic representation of a conventional live-load valve construction used to exert a compressive force on packing material; 
           [0011]      FIG. 2  is a partially cross-sectioned view of an embodiment of the present invention illustrating a live-loading assembly attached to a gland follower and a stuffing box; 
           [0012]      FIG. 3  is an exploded perspective view of a portion of the live-loading assembly shown in  FIG. 2 ; 
           [0013]      FIG. 4  is a comparative graph of packing gland stress decay with thermal cycling of an expanded PTFE (ePTFE) packing using a live-loading assembly according to an embodiment of the present invention compared with the same packing used without such live-loading assembly; and 
           [0014]      FIG. 5  is a graph illustrating API 622 fugitive emission test results for an ePTFE packing used in conjunction with a live-loading assembly according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Reference is now made to the drawings that illustrate certain embodiments of the present invention. It should be understood that the invention is not limited to the embodiments shown in the drawings. 
         [0016]    In  FIG. 1  a conventional valve  10  has a body  11  comprising a bonnet and a yoke with a sleeve or gland  12  surrounding a central axial passageway through which passes a valve stem  13 , movement of which opens and closes the valve in a conventional manner. The lower end of sleeve  12  bears on and compresses a packing structure representatively in the form of stacked compressible packing rings  20  which surround and exert radial pressure on that portion of stem  13  passing through the packing structure. Beneath the packing structure is a fixed ledge or body portion  14  against which the lower part of the packing structure bears. 
         [0017]    At the upper end of sleeve  12  is a gland follower spigot  17  in the form of an integral pair of arms  15 , 16  extending in radially opposed directions from the stem. The gland follower spigot  17  has a central bore through which stem  13  passes and a bore adjacent the radially outer end of each arm  15 , 16  to receive gland bolts  30 , 31 . Springs  32 , 33  are positioned on each bolt above its respective arm  15 , 16  and tightened by nuts  34 , 35  on the threaded ends of the bolts  30 , 31 . The compression of springs  32 , 33  which may be Belleville springs transmits an adjustable load via spigot  17  and sleeve  12  to the packing rings  20  and thereby maintains a radial pressure on stem  13  and stuffing box to prevent leakage of fluid from the valve. As is clear from  FIG. 1  there is no indication of the force being applied through the spigot  17  to the packing rings  20 . 
         [0018]      FIGS. 2 and 3  illustrate a dynamically-loaded packing system assembly  50  (which may be alternatively referred to herein as a “live-loaded” packing system assembly) according to embodiments of the present invention. Assembly  50  includes a spring cartridge body  56 , bottom and top cartridge lids  58  and  60 , a tubular spring structure preferably in the form of a stack of Belleville springs  54 , and a calibrated piston rod  52  with an exerted force scale marking  51  (referred to hereinafter simply as “scale  51 ”) suitably formed thereon. Cartridge lids  58 , 60  are secured to the ends of their associated cartridge body  56  by any suitable method including, but not limited to, welding, gluing, press-fitting or threading. 
         [0019]    The cartridge body  56  is preferably a cylindrical open-ended tube. The top lid  60  and the calibrated piston rod  52  have bores, preferably of the same size as the inner diameters of the Belleville springs  54 , to receive one of the gland bolts  30 , 31 . The clearance between the stack of Belleville springs  54  and the wall of the spring cartridge  56  is preferably equal or higher than the clearances between the Belleville springs  54  and the gland bolt. The bottom lid  58  has a bore through which a bottom end portion of the calibrated piston rod  52  downwardly passes. The clearance between the calibrated piston rod  52  and the bottom lid  58  is preferably equal to or greater than the clearances between the stack of Belleville springs  54  and their associated gland bolts  30 , 31 . 
         [0020]    The height of the spring cartridge body  56  is great enough to freely accommodate the stack of Belleville springs  54  and an annular piston crown  52 A formed on the top end of the tubular calibrated piston rod  52 . As shown in  FIG. 2 , the bottom end of the piston rods  52  bear against the top sides of the arms  15 , 16  so that the spring cartridge bodies  56  may move up and down along their associated piston rods  52 . The distance between the stack of Belleville springs  54  and the cartridge lids  58 , 60  is sufficiently large so as not to compress the springs  54  before the bolt nut  34  or  35  is tightened. 
         [0021]    The scale  51  of the calibrated piston rod  52  indicates the force being applied through the spigot  17  and sleeve  12  to the packing rings  20 . For instance, in  FIG. 2  the casing  1  is representatively the casing of a pump, a valve or other type of fluid handling device that use a packing seal to reduce or eliminate leaks. For discussion purposes the casing  1  will be considered part of a conventional valve  40 . The partially cross-sectioned view of valve  40  ( FIG. 2 ) includes an embodiment of assembly  50  of the present invention which maintains and indicates, via the scale  51 , the compressive force being exerted on the packing structure representatively in the form of the stacked packing rings  20 . The cross-sectionally depicted portion  50 A of the dynamically-loaded packing system assembly  50  clearly illustrates a partially compressed assembly where the partially compressed springs  54  thrust the calibrated piston rod  52  against the spigot  17 . The nuts  34 , 35  respectively disposed on the bolts  30 , 31  retain the live-load on the stack of packing rings  20 . 
         [0022]    When the nuts  34   35  are tightened, the spring cartridges, each comprising the top lid  60  together with the cartridge body  56  and the bottom lid  58 , are moved downwardly (using  FIG. 2  as a reference) against the resilient forces of the springs  54  that downwardly bear on the annular crowns  52 A of the calibrated piston rods  52 . The compression of the each spring stack  54  applies vertical load on the associated calibrated piston rod  52  that increases as the cartridge assembly  60 , 58 , 56  moves downwardly along the calibrated piston rod  52 . The actual spring forces being applied on the gland follower arms  15 , 16  are visually indicated on the exposed scale  51  (and/or recommended maximum and minimum operational force ranges for the packing system and/or a single recommended operational force for the packing system) with the bottom cartridge lids  58  working as indicators which move vertically along the exposed scales  51 . 
         [0023]      FIG. 4  is a graph indicating the comparative behavior of five expanded PTFE (ePTFE) packing rings installed in a packing box and exposed to temperature cycles from room temperature to 160° C. using live-loading apparatus embodying principles of the present invention (as indicated by line  110 ), and without the use of such live-loading apparatus (as indicated by the line  112 ). The left vertical axis  104  indicates the gland stress values in [MPa]. The right vertical axis  106  indicates the temperature values in [° C.], while the dotted line  108  shows the test thermal cycling. The legend  102  identifies the graph curves. 
         [0024]    The solid line  110  indicates the functionality of the dynamically-loaded packing system  50  that absorbs the packing thermal expansion and contraction. The load applied on the packing was recorded, converted to stress and displayed on the graph. The dashed line  112  shows the behavior of the same packing without using the dynamically or live-loaded packing system of the present invention. After the first thermal cycle the gland stress decreased to zero (point  114 ), and a retorque (at point  116 ) was required for the second thermal cycle. The increase in temperature led to an increase in the gland stress (at point  117 ) higher than the increase monitored in the test using the dynamically-loaded packing system  50 . After a system cool down, gland stress was again reduced to zero (at point  118 ) and the test aborted due to the system inability to maintain the gland stress. 
         [0025]      FIG. 5  is a graph indicating test results of the dynamically-loaded packing system  50  of the present invention in combination with an ePTFE packing following the test procedure described in American Petroleum Institute Standard, API 622 STD-Type Testing of Process Valve Packing for Fugitive Emissions, Second Edition. The left vertical axis  124  indicates the leakage values of methane gas in parts per million of volume [ppmv]. The right vertical axis  126  indicates the temperature values in [° C.] while the dotted line  128  shows the test thermal cycling. The legend  122  identifies the graph curves and the horizontal axis  130  the number of mechanical cycles performed. The test was conducted according to the standard with five thermal cycles with the temperature ranging from room temperature to 260° C. using the present invention. The ePTFE packing with dynamically-loaded packing system  50  endured the whole test with only one gland adjustment keeping stem seal leakage average value under 6 ppmv. The adjustment was applied when the scale  51  indicated a load force below the desired value suggested by the packing manufacturer. 
         [0026]    The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.