Abstract:
A rotary plug valve actuator comprising a mounting bracket, a ball screw mechanism pivotably mounted to the mounting bracket and a lever pivotably mounted to the ball screw mechanism. The ball screw mechanism includes a ball screw shaft and a ball nut. The ball nut moves axially on the ball screw shaft when the ball screw shaft is rotated. The lever converts the axial movement of the ball nut to rotary motion. In that way, rotation of the ball screw shaft will in turn actuate the rotary plug valve. An associated rotary plug valve assembly and an associated method of actuating a rotary plug valve are also provided.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an actuator for a rotary plug valve (or rotary ball valve) which utilizes a ball screw mechanism. An associated rotary plug valve having the rotary plug valve actuator and an associated method are also disclosed. 
     Rotary plug valves and rotary ball valves are well known and have wide application in the control of fluids in various industrial settings. The construction of the rotary plug valve usually takes the form of a cast valve body that defines an enclosed valve seat having both inlet and outlet ports. In a conventional ball valve, a spherical ball is rotatably placed in the valve seat, the spherical ball having a passageway through its diameter to provide for the flow of fluid from the inlet to the outlet side of the valve. A plug valve is constructed similarly, only the plug is not spherical. See U.S. Pat. No. 4,802,652, the disclosure of which is incorporated by reference herein. 
     The ball or plug is rotated by means of an operator mechanism, sometimes called an actuator. One type of actuator is shown in U.S. Pat. No. 4,802,652 which simply provides a handle for applying torque to the ball or plug. For larger plug or ball valves, a mechanism is typically used to apply the torque. One known mechanism is a worm gear actuator. As is well known, the worm gear mechanism consists of a screw shaft (&#34;worm&#34;) which is engaged by a rotating gear. 
     The worm gear mechanism, while effective in increasing the mechanical advantage of the actuator, has numerous disadvantages. A first disadvantage is that the worm gear mechanism involves sliding motion between the worm and the gear. This means that much of the torque applied to the gear is lost due to friction, thus making the worm gear mechanism, even when new, difficult to turn. Of course, as the worm gear mechanism ages and rusts, it is even more difficult to turn. A second disadvantage is that the worm and gear are often exposed to dust, dirt and moisture, making it difficult to keep lubricant thereon with the attendant greater difficulty in turning the worm gear mechanism. 
     A ball screw mechanism is a known mechanical device that consists of a rotatable shaft having disposed thereon a ball screw nut. See, e.g., U.S. Pat. No. 3,628,397; Warner Electric Catalog (1983); and Noor Industries Catalog (1991), the disclosures of all three of which are incorporated herein by reference. The ball screw mechanism uses rolling contact (similar to ball bearings) instead of the sliding contact utilized in the worm gear mechanism. Thus, the ball screw mechanism is much more efficient than the worm gear mechanism. 
     Despite the long existence of the ball screw mechanism, no one, until now, has suggested its use in association with ball or plug valves. 
     Thus, there remains a need for a rotary valve actuator that is efficient and avoids the problems of the prior art worm gear mechanism. 
     SUMMARY OF THE INVENTION 
     The rotary plug valve actuator disclosed and claimed herein satisfies the above-mentioned needs. The rotary plug valve actuator comprises a mounting bracket, a ball screw mechanism pivotably mounted to the mounting bracket and a lever pivotably mounted to the ball screw mechanism. The ball screw mechanism includes a ball screw shaft and a ball nut. The ball nut moves axially on the ball screw shaft when the ball screw shaft is rotated. The lever converts the axial movement of the ball nut to rotary motion. In that way, rotation of the ball screw shaft in turn actuates the rotary plug valve. 
     The invention also comprehends a rotary plug valve assembly comprising a rotary plug valve having an inlet portion, a valve seat, an outlet portion and a plug valve disposed in the valve seat. The assembly further comprises a rotary plug valve actuator similar to that described above. 
     Finally, a method of actuating a rotary plug valve is disclosed in which a rotary plug valve assembly including a rotary plug valve having mounted thereon a rotary plug valve actuator is provided. The rotary plug valve actuator is similar to that described above. The method further comprises rotating the ball screw shaft to actuate the rotary plug valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full understanding of the invention can be gained from the following description of the preferred embodiment when read in conjunction with the accompanying drawings in which: 
     FIG. 1 is a perspective view of the rotary plug valve actuator mounted on a rotary plug valve. 
     FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1. 
     FIG. 3 is a top plan view of the rotary plug valve actuator showing the different positions of the actuator in phantom lines. 
     FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 3. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIGS. 1-4, a rotary plug valve actuator 10 in accordance with the invention is shown mounted on a rotary plug valve 12. As the rotary plug valve 12 is conventional and well known in the art, it is not shown in full in FIG. 1. It will be appreciated, though, that the rotary plug valve 12 includes a valve body 14 that defines a valve seat (not shown) having an inlet port 16 and an outlet port 18 (FIG. 3). A plug (not shown) defining a transverse passageway is mounted in the valve seat. As is well known, fluid flow through the valve 12 is permitted when the plug is in an open position; i.e., when the passageway is provided between the inlet and outlet port. The valve is closed by rotating the plug to the closed position, i.e., when the passageway is generally perpendicular to the inlet and outlet ports, so that fluid is not able to flow through the passageway. 
     It will be appreciated that although the invention is described as a rotary plug valve actuator that it also can be used in association with a rotary ball valve actuator. Thus, as used herein, the term &#34;rotary plug valve&#34; includes rotary ball valves or any other types of rotary valves having the same function and operation as a rotary plug valve. 
     Referring now specifically to FIG. 1, the rotary plug valve actuator 10 comprises a mounting bracket 30, a ball screw means 34 pivotably mounted to the mounting bracket 30 and a lever means 38 pivotably mounted to the ball screw means 34. The lever means 38 consists of a collar 40 which is secured to a shaft 42 that extends from the valve plug (not shown) through the upper portion of the valve body 14. The collar 40 is aligned to fit over a key 48 and is secured to the shaft 42 by set screws 46, two of which are shown in FIG. 1. It will be appreciated that the rotary motion of the lever means 38 is transmitted through the collar 40 in order to rotate the shaft 42. This in turn rotates the valve plug into different positions (i.e., from fully open to fully closed or positions therebetween) as is explained in further detail below with respect to FIG. 3. 
     The mounting bracket 30 consists of a horizontal flange 50 which is bolted to the valve body 14 by means of bolts, one of which, bolt 52, is shown in FIG. 1. Two spaced apart vertical supports 54 and 56 are secured to the flange 50, as by welding, and cross member 58 is secured to the upper portion of the vertical supports 54 and 56 by means of bolts 60 and 62, respectively. The flange 50, vertical supports 54, 56 and cross member 58 form a space 64 in which the ball screw means 34 is mounted and can be rotated therein. It will be appreciated by those skilled in the art that a variety of structures or types of mounting brackets may be provided. 
     Referring to FIG. 2, the ball screw means 34 includes a bearing housing assembly 70. The bearing housing assembly has two bearings 72 and 74 in which the shaft 76 of the ball screw means 34 is journalled. 
     A handle assembly 80, which is shown in FIG. 1 as a wheel having spokes, is mounted at one end of the shaft 76 by means of a set screw 82. A key 84 is preferably provided to align the handle assembly 80 to the shaft 76. The ball screw shaft 76 is affixed and held in position to the bearing housing by means of a locknut 86. 
     As can be seen in FIGS. 1 and 2, the bearing housing assembly 70 is pivotably mounted to the mounting bracket 30 about a pivot line or axis defined by upper pivot pin 90 and a lower pivot pin 92. This mounting arrangement permits the bearing housing assembly 70 and thus the ball screw means 34 to pivot in space 64 when the valve actuator is operated, as is explained below with respect to FIG. 3. The pivot pins 90 and 92 are disposed along a line or axis generally parallel with the axis of rotation of the rotary plug valve. 
     The ball screw means 34 further consists of the ball screw shaft 76 and a ball screw nut 100, which is shown in phantom in FIG. 3 and in cross-section in FIG. 4. The ball screw shaft 76 and ball screw nut 100 make up a well known mechanical device that converts the rotation of the ball screw shaft 76 into the linear motion of the ball screw nut 100. Such a mechanical device is manufactured by Warner Electric, Troy, Michigan (see Warner Electric Catalog (1983), which is incorporated herein by reference). 
     The ball screw means 34 further consists of a bellows assembly 110 to protect the ball screw shaft 76 and a shaft cover 112 that receives and protects the shaft 76 when it is in its extend position (see FIG. 3). 
     Referring now to FIG. 4, the ball screw nut 100 is shown mounted to the lever means 38 by means of screw threads 114 disposed on the ball screw nut 100 which are complementary to threads 116 on horizontal member 118 of the lever means 38. The lever means 38 includes a top lever arm 120 and a bottom lever arm 122. The arms 120, 122 are secured by screws, such as screws 124, 126, to a bar 130 which in turn is mounted, as by welding, to the shaft collar 40. The free edge of the arms 120, 122 are pivotably mounted to the ball screw nut 100 by means of pivot pins 140, 142. The pivot pins 140, 142 are disposed on a line generally parallel with the axis of rotation of the rotary plug valve. 
     Referring now to FIG. 3, the operation of the valve actuator is explained. As shown in solid lines, when the plug valve is closed, the lever means 38 is positioned furthest to the left, i.e., in a position furthest from the bearing housing assembly 70. It will be appreciated that the plug valve could be operated in the opposite direction, i.e., open when the lever means is positioned furthest to the left and closed when the lever means is furthest to the right. In order to close the plug valve, the handle assembly 80 is rotated, thus rotating the ball screw shaft 76 which in turn creates linear motion of the ball screw nut 100. As can be seen by the phantom lines in FIG. 3, this motion causes the lever means 38 to rotate about the plug valve shaft axis toward the bearing housing assembly 70 to the middle or half open position. In order to accommodate this movement, the ball screw means 34 rotates about pivot pins 90 and 92 to the position shown in phantom on FIG. 3. This is accomplished because the bearing housing assembly 70 is pivotably mounted to the mounting bracket and the lever means 38 is pivotably mounted to the ball screw means 34. 
     Further rotation of the handle assembly 80 fully opens the plug valve. The lever means 38 is in the furthest right position (i.e., closest to the bearing housing assembly 70) shown on FIG. 3, with the ball screw means position (not shown) being in the same alignment as when the plug valve is in the fully closed position. It will be appreciated that the ball screw means 34 has an axis of rotation disposed in a plane that is generally perpendicular to a plane including the axis of rotation of the rotary plug valve. 
     In order to indicate the position of the plug valve, an indicator 160 is mounted on the shaft collar 40. The indicator 160 points in the direction of the passageway of the plug valve. As shown in FIG. 3, the indicator 160 shows that the passageway is oriented perpendicularly to the fluid flow, thus the plug valve is closed. Once the plug valve is fully opened, the shaft collar 40 and thus the indicator is rotated 90°, as shown in phantom in FIG. 3. In the fully opened position, the passageway is oriented generally parallel to the fluid flow, thus the plug valve is indicated by the position of the indicator to be opened. 
     EXAMPLE 
     In order to illustrate the advantages of the invention, the torque required to rotate a conventional worm gear actuator was compared to the torque required to rotate the rotary plug valve actuator of the invention. A conventional worm gear actuator was separately mounted to three separate valves and the torque required to rotate these valves was measured. Two sets of experiments were run, the first with the gears in a dry or non-lubricated state and the second with the gears being lubricated. The rotary plug valve actuator of the invention was separately mounted to each of the same three valves and the torque required to rotate the valve was measured. 
     The results of the experiment are reported below: 
     
         ______________________________________    Torque (in ft-lbs)    Worm Gear Actuator  Rotary Plug    Dry    Lubed        Valve Actuator______________________________________Valve #1   50-55    30-40         5-10Valve #2   300-350  230-240      75-90Valve #3   65-75    35-45        1-5______________________________________ 
    
     As can be seen from the above results, the rotary plug valve actuator requires on the average from 70-80% less torque to rotate the valve than the conventional worm gear actuator. 
     While the invention has been described in terms of preferred embodiments, the claims appended hereto are intended to encompass all embodiments which fall within the spirit of the invention.