Abstract:
A valve closure system ( 30 ) for operating a valve ( 32 ) of a fluid-holding cylinder (CYL) between an open and a closed position to allow and disallow communication of the interior of the cylinder through the valve. A coupler ( 118 ) engages and rotates a stem ( 40 ) of the valve. An electric motor ( 92 ) rotates the coupler. A square tube ( 102 ) on the motor housing surrounds the coupler. A bracket ( 50 ) mounts on the valve body. The parts ( 50, 102 ) have respective walls shaped to mutually telescopically engage when, with bracket ( 50 ) mounted on the valve, the motor housing has been properly circumferentially and axially aligned with the bracket and then advanced to move the coupler toward engagement with the valve stem. The parts ( 50, 102 ) may be pinned together by a hitch pin ( 54 ).

Description:
REFERENCE TO A RELATED APPLICATION AND PRIORITY CLAIM 
   This application claims the priority of Provisional Application No. US60/658,617, filed on 4 Mar. 2005 naming Richard D. Fortino as inventor. 

   FIELD OF THE INVENTION 
   This invention relates to a valve closure system comprising an electric motor for turning a rotary actuator of a valve to operate the valve from open to closed. Such valve closure systems allow valves of vessels, such as cylinders and containers, that hold fluids, such as industrial gases for example, to be quickly operated from a remote location. 
   Various types of transportable vessels are used for packaging various commercial and industrial gases at superatmospheric pressure. One type of vessel is a gas cylinder, an example of which is an elongate metal tank adapted to contain gas at relatively high pressure. An upper axial end of the cylinder has a neck containing an opening to the interior. A shut-off valve is mounted in closure of the neck opening. Another type is a container, a vessel that may have substantially larger volume than a cylinder. A container may have several such shut-off valves each mounted in closure of a respective opening in the container wall. 
   A representative shut-off valve comprises a first port fitted in sealed relation to an opening in a vessel wall, a second port, and a valve mechanism that is operable via an external actuator, handle, or tool, to allow and disallow fluid communication between the two ports. The second port is externally available for connection to a gas supply source when the cylinder is to be filled and for connection to a gas utilization system at a facility that uses gas stored in the cylinder. The valve mechanism comprises a stem that is rotated by the external actuator, handle, or tool to open and close the valve. An external actuator may be either manual or powered. An electric- or pneumatic-powered prime mover is an example of a power actuator. A wrench is an example of a hand tool for turning the valve stem. 
   The representative valve may be a globe style valve whose stem is rotatable more than one full turn between closed and full open positions. Opening the valve allows contained gas to pass from the vessel by entering the first port, flowing through the valve, and exiting via the second port. In such case, the first port forms a gas inlet connected to the vessel, and the second port a gas outlet. The gas outlet may be connected via a conduit to a point of use of the gas. 
   Such vessels can hold gases that may be considered hazardous, examples of such gases including chlorine and sulfur dioxide. A facility that utilizes one or more of such gases in a process, or processes, conducted at the facility may, for example, have any number of such vessels containing the same or different gases on the premises. When connected to a gas handling system at the facility, such vessels are able to deliver gas, or gases, into the system once their shut-off valves have been opened. 
   Because of inherent characteristics of certain gases, vessels that contain them may be housed in locations that are remote from attending personnel, and/or the vessels may be in use at times when personnel are absent. 
   When a vessel, or vessels, is, or are, in use at a facility, and gas leakage is detected, it may be appropriate to shut off all vessels in an attempt to minimize further gas leakage. 
   Accordingly, an automatic gas leak detection and valve shut-off system may be employed at a facility to address such a situation. Such a system may include a power actuator associated with the shut-off valve of each vessel. Examples of known valve closure systems include electromechanical actuators and pneumatic actuators. 
   Commonly owned U.S. Pat. Nos. 6,170,801 and 6,840,503 disclose valve closure systems for gas-containing vessels. When mounted on a vessel, a valve closure system associates with a valve having a rotatable stem that opens and closes the valve. The closure systems described in those patents comprise mounting brackets and air motors. With the valve open, the bracket is fit to the valve and a coupling on an external end of the air motor shaft is fit to the valve stem. The long axis of the air motor is coincident with the axis of the stem, or at a right angle to the valve stem. When pressurized air is delivered to the air motor, the motor shaft rotates the stem in a sense that closes the valve. 
   In certain facilities that use those types of valve closure systems, compressed air either may not be readily available or else may not be a preferred power source for operating the valve closure systems. In such instances, an electromechanical operator like an electric motor may be preferred. 
   Because a valve closure system must be removed when a gas cylinder is empty and thereafter installed on a fresh replacement cylinder, it is believed important for an electric-motor-operated valve closure system for such gas cylinders to be relatively light in weight and convenient to remove and install. Because space considerations may also be important in such facilities, minimizing the overall dimensions of a valve closure system is believed conducive to customer acceptance of a particular design. For example, the long axis of an electric motor affects the overall length of a valve closure system, and keeping that dimension as small as possible is apt to be desired by certain users. 
   When an electric motor is direct coupled in-line with a valve stem, the motor shaft will turn the valve stem in one-to-one correspondence (i.e. a 1:1 ratio) unless there is an intervening gear reduction mechanism. By providing a gear reduction mechanism, a smaller motor can be used to meet the valve torque requirements. 
   Parts for mounting valve closure systems on gas cylinders may, but do not necessarily, include a standard part commonly called a yoke that is clamped to the valve body and typically serves to embrace a fitting that connects a hose to a port of the valve. After having been fitted onto a valve body, the yoke is fastened in place by tightening a screw in a threaded hole in one side of the yoke to clamp the yoke to the valve body. Additional mounting parts serve to locate and support the valve closure system on the valve body and provide for the shaft of the operator to assume operative coupling with the valve stem. 
   The in-line coupling of the operator shaft to the valve stem typically has a non-circular transverse cross section that fits to a similarly shaped stem to provide for torque transmission to the stem. When the valve closure system is being installed, an installer may have an obstructed view of the coupling and stem and therefore an inability to easily judge when proper circumferential registration between the stem and coupling is attained so that the coupling can come into driving engagement with the valve stem. If the coupling is out of registration with the stem, the installer must perform some sort of manipulation in order to secure registration, and that may be an inconvenient task whose avoidance would be desirable. 
   Also, a valve closure system should be sufficiently rugged and durable for the environmental and operating conditions that it is expected to encounter when placed in use. 
   SUMMARY OF THE INVENTION 
   The present invention relates to further improvements in valve closure systems for fluid-containing vessels, the term “fluid” including both liquids and gases. 
   Briefly, and without limiting the scope that is defined by the claims, the invention comprises, in a disclosed presently preferred embodiment: a novel organization and arrangement of mounting parts, that may include a standard yoke, for enabling personnel to conveniently install and remove a valve closure system on and from a gas cylinder; and an electric motor that not only can turn the valve stem of a gas cylinder shut-off valve for opening and closing the valve, but also can be conveniently jogged to allow a coupling on the end of the motor shaft to readily attain proper circumferential registration with the valve stem during installation of the valve closure assembly on a gas cylinder. 
   The inventive valve closure system is also relatively compact, light-weight, and durable. It can be used on a gas cylinder whose valve turns about a vertical axis and also on a gas cylinder whose valve turns about a horizontal axis. 
   The preferred embodiment of the inventive closure system is well suited for use with known, and commonly used, gas shut-off valves, although certain principles are generic to use of the inventive system with different forms of shut-off valves. Certain principles of the invention may also extend to valve closure systems in which the fluid storage medium is a form of storage vessel other than the particular container and cylinder vessels mentioned above. 
   One generic aspect of the invention relate to a valve closure system for operating a valve of a fluid-containing vessel between an open and a closed position to allow and disallow communication of the interior of the vessel through the valve. The valve closure system comprises: an operating part shaped to engage and rotate a rotary actuator protruding from a valve body to operate the valve from one position to another when the valve closure system is associated with the valve; a motor for rotating the operating part; a walled located part disposed on a housing of the motor; and a walled locating part shaped for mounting on the valve body, the walled parts respectively comprising respective walls shaped to mutually telescopically engage when, with the locating part mounted on the valve, the motor housing has been properly circumferentially and axially aligned with the locating part and then advanced to move the operating part toward engagement with the rotary actuator of the valve. 
   Another generic aspect relates to a valve closure system for operating a valve of a fluid-containing vessel between an open and a closed position to allow and disallow fluid flow with respect to the interior of the vessel. The valve closure system comprises: an electric motor for rotating an operating part that is shaped to engage a rotary actuator of a valve for operating the valve from one position to another when rotated by the motor; a mounting via which a housing of the motor is constrained against rotation relative to a body of the valve when the motor rotates the operating part while the latter is engaged with the rotary actuator; and a jogging switch disposed on the motor housing for jogging the motor to turn the operating part to a proper position for engagement with the rotary actuator of the valve when the motor is being operatively associated with the valve. 
   Still another generic aspect of the invention relates to a method of associating a motor-operated valve closure system with a valve of a fluid-containing vessel for operating the valve, via a rotary actuator of the valve, between an open and a closed position to allow and disallow communication of the interior of the vessel through the valve. The method comprises: circumferentially and axially aligning a located part on the motor with a locating part on the valve and advancing the motor toward the valve to mutually telescopically engage respective walls of the located and locating parts and couple an operating part coupled to the motor to the rotary actuator to couple the rotary actuator to the motor. 
   The accompanying drawings, which are incorporated herein and constitute part of this disclosure, illustrate a presently preferred embodiment of the invention, and together with the written description given herein disclose principles of the invention in accordance with a best mode contemplated at this time for carrying out the invention. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view showing a presently preferred embodiment of the inventive valve closure system mounted on a gas cylinder valve. 
       FIG. 2  is another perspective view looking in a different direction. 
       FIG. 3  is an elevation view in the direction of arrows  3  in  FIG. 1 . 
       FIG. 4  is a cross section view in the direction of arrows  4 - 4  in  FIG. 3 . 
       FIG. 5  is an exploded perspective view of the valve closure system and the valve. 
       FIG. 6  is a perspective view useful in understanding the installation and removal sequences for installing and removing the valve closure assembly on and from the valve. 
       FIG. 7  is a perspective view of a multi-piece part corresponding to, but different from, one of the parts previously described. 
       FIG. 8  is a top view in the direction of arrow  8  in  FIG. 7 . 
       FIG. 9  is a perspective view of one of the pieces of the part shown in  FIGS. 7 and 8 . 
       FIG. 10  is a front elevation view of another multi-piece part corresponding to, but different from, another of the parts previously described. 
       FIG. 11  is a view of one of the pieces of the part of  FIG. 10 , as taken in the direction of arrows  11 - 11  in  FIG. 10 . 
       FIG. 12  is a perspective view of another of the pieces of the part shown in  FIG. 10 . 
       FIG. 13  is a side elevation view of the parts of  FIGS. 7 and 10  in mutual association mounting a motor of the valve closure system on a valve. 
   

   DETAILED DESCRIPTION 
   The drawing  FIGS. 1-6  illustrate one presently preferred embodiment of cylinder valve closure system  30  according to principles of the invention intended for association with a cylinder valve  32 . Those drawings show a vertical installation, but the closure system can also be installed horizontally when the valve axis is horizontal. 
   Valve  32  is a commercially available cylinder tank shut-off valve that comprises a body  34  having a first port  36  at the bottom and a second port  38  at a side. Port  36  is adapted to fit in sealed closure of an opening in a neck at the top of a gas cylinder CYL (not shown in  FIGS. 1-6 , but shown in phantom in  FIG. 13 ). Port  38  is adapted for connection to a gas supply source when the cylinder is to be filled with gas. When the cylinder is in use at a facility, port  38  is connected to a gas handling system through which gas can flow from the cylinder to a point of use at the facility. 
   Valve  32  further includes an operating mechanism comprising a valve element within body  34  that is operated to open and close an internal gas flow path between ports  36  and  38 . The valve element is operated by turning an actuator, which for the illustrated valve, is a stem  40  on the exterior of body  34 . The turning of stem  40  occurs as rotation about an axis  42 . Stem  40  has a polygonally-shaped transverse cross section (a square shape for example) that can be engaged by a complementary shaped tool or socket for turning the stem. At the location where stem  40  protrudes from valve body  34  is a hexagonal-shaped head  44  that is concentric with axis  42 . Immediately below, and concentric with head  44 , body  34  has a cylindrical wall  46  of smaller diameter that allows portions of head  44  to protrude radially outwardly and overhang wall  46 . 
     FIG. 6  shows a motor assembly  48 , a bracket  50 , a yoke  52 , and a hitch pin  54 . Yoke  52  is shown in engagement with a fitting  56  on one end of a hose of conduit  58  forming a portion of the gas handling system to which port  38  of valve  32  is connected when in use at a typical facility that uses valve closure systems. Yoke  52  is a standard part for that may be used on gas cylinder valves at such facilities and comprises what is essentially a four-sided rectangular frame having two longer sides  60 ,  62  and two shorter sides  64 ,  66 . Side  64  has a discontinuity at its center that allows that side to embrace fitting  56 . Side  66  has a threaded hole at its center into which a screw  68  is threaded. Turning of screw  68  via a wrench surface  70  at one end in opposite directions advances and retracts a clamp  72  at the other end for clamping and unclamping yoke  52  to and from valve body  34 . In this way, yoke  52  accomplishes its usual purpose of holding fitting  56  on valve  32  after the fitting has been threaded and properly tightened to port  38  typically with a suitable sealing gasket between the port and the fitting. In certain valves, port  38  is externally threaded. 
   As will become apparent from following description, yoke  52  may be considered part of the valve closure system shown in  FIGS. 1-6  because in so holding fitting  56  to valve body  34 , the yoke constrains movement of the bracket  50  on the valve body while also preventing removal of the bracket from the valve body. General principles of the invention however do not require that such a standard yoke be present. 
   Bracket  50  comprises a length of three-sided channel stock having side walls  74 ,  76 , and  78 . A metal piece  80  is formed to have a right-angle bend  81  in  FIG. 4 . To one side of bend  81 , piece  80  has a collar  83  containing a circular through-hole  82 . To the other side of bend  81 , piece  80  is notched to provide clearance for valve  32  while endowing the piece with two legs  85  that join respectively with side walls  74 ,  78  to secure piece  80  to the channel stock. Through-hole  82  is large enough to fit over port  38  while side walls  74 ,  76 , and  78  bound the valve on three sides. Aligned through-holes  84 ,  86  at the upper corners of side walls  78 ,  74  opposite piece  80  are clear of the valve body when bracket  50  is installed on the valve. 
   Motor assembly  48  comprises a multiple part housing  90  that provides an enclosure for an electric motor  92  and a casing  93  that contains a planetary gear drive. Housing  90  comprises a cylindrical side wall  94  having an open upper end closed by a removable cap  96  and a lower end to which a bracket  98  is fastened.  FIG. 5  shows bracket  98  to comprise a flat circular ring  100  and a length of square tube stock  102  joined to and extending downward from and coaxial with ring  100 . Tube stock  102  comprises four apertured side walls dimensioned to provide the tube stock with a telescopic fit to bracket  50 . 
     FIG. 5  also shows an end plate  104  that has four locator tabs  106  protruding radially beyond the nominal inside diameter of side wall  94  at 90° intervals about a main longitudinal axis  108  of motor assembly  48 . End plate  104  is one end part of casing  93 . Motor  92  is secured to another end part of the gear drive casing opposite end plate  104 . Motor  92  and casing  93  are secured in proper position in motor assembly  48  by assembling them into the housing through the open lower end of side wall  94  to lodge tabs  106  in mating notches  110  arranged at 90° intervals about axis  108  in the end margin of side wall  94 . Bracket  98  is then placed axially of the lower end of side wall  94  and advanced toward the side wall to capture tabs  106 . Four screws  112  pass through aligned clearance holes  114  in ring  100  and in the four tabs  106  and are tightened in tapped holes  116  in side wall  94 . 
   A coupler  118  is assembled to an output shaft  120  of motor  92  in a manner that allows the coupler to move axially on the shaft without falling off. A spring  122  is disposed between end plate  104  and an inner end of coupler  118  effectively resiliently biasing the coupler in the direction away from the interior of housing  90  while allowing the coupler to move axially toward the interior against the spring bias force. Coupler  118  has a circumferentially keyed connection to shaft  120  and provides a socket having a shape for fitting to stem  40  so that motor torque can be transmitted through the coupler to turn stem  40 . The end portion of shaft  120  has an elongate slot  124  parallel to the shaft length. A spring pin (not shown) passes through a circular radial hole in the coupler wall, through slot  124 , and a circular radial hole in the opposite portion of the coupler wall causing the coupler to be kept on the shaft end, but allowing the coupler to position itself axially along the shaft end. The lost motion allows for some tolerance in length of the valve stem and the extent of stem displacement while turning. The limited displacement travel serves to accommodate axial travel of the valve stem as the stem is being rotated, but it does not allow coupler  118  to lose driving engagement with the valve stem while the system remains installed. 
   The planetary gear drive provides a gear reduction between the motor and the valve stem to amplify the motor torque to proper level for turning the valve stem. The use of a planetary gear drive also contributes to robustness of the motor assembly. 
   Cap  96  has a dome  126  surrounding a circular walled cavity  128 . A push-button switch  130  is mounted on a bottom wall of the cavity. The button actuator  132  is on the outside of the housing interior where it can be depressed by thumb or finger. It does not however protrude above the rim of dome  126 , thereby requiring a person&#39;s thumb or finger to enter the open top of the cavity in order to actuate switch  130 . The mounting is made weather-tight by an O-ring gasket  133  sealing the switch housing to the cap. 
   Electric wires inside a conduit  134  provide power to switch  130  and motor  92 . Switch  130  and motor  92  are arranged in circuit with power supplied by the electric wires such that pressing button  132  to actuate switch  130  causes motor shaft  120  to turn only in a direction that will act to open valve  32 . This assures that the installer will not inadvertently close an otherwise open valve, an important consideration at certain facilities such as water treatment plants. The circuit arrangement provides for the actuation of switch  130  to energize a solenoid that operates contactors through which current is carried to the motor. In that way, the switch carries only a small current because the larger motor current doesn&#39;t pass through the switch. And as mentioned before the actuation of switch  130  causes the motor to operate only in a direction that will open a valve so that an already open valve will not be inadvertently closed by jogging the motor when the coupler is engaged with the valve stem. The solenoid is located in a control panel that is remote from the motor assembly. 
   Conduit  134  is secured in a weather-tight manner to motor assembly  48  via a fitting  136  that tightened in a threaded hole in side wall  94 . In addition, there are electric wires from a remote control panel that will operate the valve closure system to close an open valve in situations where valve closing is called for. 
   Cap  96  has a series of six through-holes  138  in its outer margin. Six screws  140  pass through the six holes  138  and are tightened in tapped holes in the upper end of side wall  94  to fasten cap  96  to the side wall thereby enclosing motor  92  at that end of the motor assembly. An O-ring gasket  142  is received in a circular groove in the radially outer surface of a short cylindrical wall  144  that fits closely to the inside of side wall  94  to make the cap-to-side wall joint weather-tight. 
   An O-ring gasket  146  seals the motor housing to side wall  94  in a similar way at the lower end of the motor assembly. 
   The foregoing description now allows the installation and removal of the valve closure system to be explained. First, with screw  68  backed off, the distance between clamp  72  and side  64  of yoke  52  allows the yoke to be placed over valve  32  until it rests on the gas cylinder (not shown). Then bracket  50  is placed on the valve by aligning hole  82  with port  38  and moving the bracket radially to insert the port into the hole. Although collar  83  has a slightly loose fit around the outside of port  38 , bracket  50  can turn only a very limited amount about the axis of port  38  due to sides  60  and  62  of the yoke presenting interference to the vertical sides of the collar. Once the collar has been placed over and around outlet port  38 , fitting  56  can then be connected. 
   Next yoke  52  is raised off the gas cylinder to the position shown by  FIG. 4 , and screw  68  is tightened to clamp the yoke to the valve body and engage fitting  56  as shown. This also prevents bracket  50  from falling off the valve. Motor assembly  48  is then placed over the valve with its axis generally aligned with valve axis  42  and lowered to telescope tube  102  inside the channel of bracket  50 . In this way, bracket  50  forms a locating part for locating tube  102 , the latter part being the located part. 
   Operative engagement of coupler  118  with stem  40  can be attained only when they have proper circumferential registration. If circumferential registration exists as the motor assembly is being placed on the valve, coupler  118  will attain rotatable coupling with stem  40 . If the coupler and stem are out of registration, the coupler will contact the stem  40 , but without attaining rotatable coupling, in which event button  132  can be depressed to jog motor  92  until registration occurs at which time the motor assembly may drop down slightly in a vertical installation as shown. The weight of the motor assembly will be borne by abutment of end plate  104  with ring  100  at the upper ends of the bracket  98  side walls, and resulting transmission of that weight through bracket  50  to port  38  by virtue of collar  83  resting on the port. Weight is not borne through coupler  118  although the coupler&#39;s engagement with the valve stem stabilizes the mounting. 
   For keeping the motor assembly in place on the valve, hitch pin  54  is inserted through hole  84  to pass through aligned holes  148  in opposite sides of tube  102  and then hole  86 . The placement of holes  84 ,  148 , and  86  provides for hitch pin  54  to clear valve  32 . With the hitch pin in place, the motor assembly cannot be removed unless the hitch pin is first extracted. Removal of the valve closure system from the valve can be easily accomplished by lifting the motor assembly off the valve after the hitch pin has been extracted. 
   The telescopic engagement between the channel of bracket  50  and tube  102  keeps substantial axial alignment of the motor assembly to the valve stem as the motor assembly is being placed. Once the motor assembly has been placed, none of its weight is transmitted to yoke  52 , and bracket  50  is free of contact with the yoke. 
     FIGS. 7-13  illustrate brackets  150 ,  198  representing modified forms of brackets  50  and  98 . 
   Bracket  150 , like bracket  50 , comprises three side walls  174 ,  176 , and  178 . It is a formed sheet metal part of suitable thickness. A piece  180  that is shown by itself in  FIG. 9  is welded to bracket  150  to provide a collar  183  containing a circular through-hole  182 . Piece  180  is a machined metal piece. Aligned through-holes  184 ,  186  are present at the upper corners of side walls  178 ,  174  but those two side walls unlike side walls  78 ,  74  are not rectangular in shape because the lower corners have been cut away. 
   Piece  180  differs from piece  80  by having full side walls  185  rather than merely two legs  85 . Certain features of piece  180  have significance in relation to bracket  150  and to valve  32 . The upper portions  185 A of walls  185  have reduced thickness that provides horizontal dimensional clearance to the nuts of certain valves from which the valve stems emerge. Notches  185 B and chamfers  185 C provide clearance and facilitate installation for certain valves. 
   For controlling the horizontal dimension between the inner face of collar  183  and the centerline of through-holes  184 ,  186  so that the inner collar face can be disposed against the portion of the valve body adjoining port  36  and the hitch pin can pass through the telescoped brackets with a desired closeness to the valve body on the side opposite port  36 , a ridge  183 A is present at the top of the side wall containing the collar. A rectangular opening  183 B is also present in that same side wall above through-hole  182  to provide for clearance to the valve. For controlling the vertical dimension between the centerline of through-hole  182  and the centerline of through-holes  184 ,  186 , the height of ridge  183 A is chosen such that the lower surface of the ridge and the lower surface of side wall  176  will be located against a common horizontal surface in a welding jig before the machined and formed pieces are welded together around the outside of the overlapping margins of three side walls. 
   Bracket  198 , like bracket  98 , has a flat circular ring  200 , corresponding to ring  100 , and a square tube  202 , corresponding to tube  102 , joined to and extending downward from, and coaxial with, ring  200 . A face of ring  200  has a shallow recess  201  for locating tube  202  to it prior to the two pieces being welded together. Tube  202  comprises four apertured side walls dimensioned to provide the lower end portion of the tube below a shoulder  203  with a telescopic fit to bracket  150 . One of the apertures  205  allow installer viewing of coupler  118  through the telescoped brackets. Shoulder  203  rests on the upper edge of bracket  150  when the motor is mounted on the valve. Through-holes  248  in opposite side walls align with through-holes  184 ,  186  to provide for passage of the hitch pin through both brackets to pin them together when the motor is in place on the valve. 
   A bent tab  207  containing a threaded through-hole  209  forms a continuation of the one side wall of tube  202  that is opposite collar  183 . A thumbscrew  211  is threaded into hole  209  and can be tightened to cause its tip to bear against the backside of the valve body. In doing so the thumbscrew provides an adjustment for minimizing non-parallelism of the motor axis to the valve stem axis while relieving some of the weight being applied to the valve port on which collar  183  bears. Although it was mentioned in connection with  FIGS. 1-6  that the valve stem doesn&#39;t bear any of the weight of the valve closure system, certain valve stems can bear some or all of the weight. 
   While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.