Back-seating of rotary valve stem

A rotary valve assembly comprising a valve body having a stem passageway in communication with the valve body cavity which contains a closure member for selectively closing or opening the fluid flow passageway intersecting the valve body cavity. A valve operator consisting of a reciprocatable and rotatable stem passing through the stem passageway is connected to the closure member so that when the stem rotates, the closure member rotates together with the stem. The stem is provided with a back-seat and the valve operator reciprocates the stem to unseat and reseat the stem onto the stem seat located on the valve body surrounding the stem passageway in order to seal the stem passageway from the valve body cavity. Sealing of the stem passageway isolates the stem packing from the fluid in the valve body cavity, prevents fugitive emissions related to stem leakage and prolongs the useful life of the stem packing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to valve assemblies of the rotary type in 
which the stem is provided with a mechanically loaded back-seat with 
externally variable stem seating force so as to prevent fugitive emissions 
by isolating the stem packing from the fluid in the valve body cavity and 
thus prolonging the useful life of the stem packing. 
2. Brief Description of Prior Art 
Valves are used in large numbers in the process industry handling fluids of 
all kinds and they are the major contributor to overall fugitive emissions 
in the industry. Fugitive emission is referred to any fluid, hazardous or 
otherwise, leaking through any part of a closed piping system. Leakage 
around the valve stem through the stem packing is a significant cause of 
fugitive emissions. The Clean Air Act establishes stringent guidelines for 
control of fugitive emissions. 
A common method of controlling leakage around the valve stem is to provide 
a stem seal that includes the use of a stuffing box that is packed with 
material such as graphite or fluoropolymers. The bolted gland of the 
stuffing box exerts compressive force on the packing material which in 
turn exerts radial thrust around the stem periphery to seal the stem 
passageway. When the stem packing is newly installed, the leakage around 
the stem is minimal. But when the valve is used, the stem reciprocates 
and/or rotates inside the packing material which eventually wears out and 
the radial thrust around the stem periphery relaxes. The decreased radial 
thrust reduces the sealing effectiveness around the stem, thereby 
permitting fluid in the valve body cavity to leak along the stem 
passageway. In order to reduce fluid leakage, the stuffing box packing is 
tightened axially in order to increase the radial sealing thrust around 
the stem. The stuffing box packing is also replaced periodically with new 
packing material. Another method to reduce fugitive emissions around the 
stem is to put stem packing under "live loading" with springs which 
provides a constant compressive force on the stem packing. 
The above method of stem packing only controls fugitive emission and does 
not prevent it. Fugitive emission around the stem can be prevented only by 
isolating the stem packing from the fluid in the valve body cavity. 
In valves that are in use today, only non-rotary valves with reciprocating 
stems are provided withback-seats that can be loaded with externally 
variable stem seating force. So far it has been found very difficult and 
elusive to provide back-seats on rotary valve stems that can be loaded 
with externally variable stem seating force that automatically adjusts to 
wear of the seating surfaces. Some current rotary valves like plug and 
ball valves are provided with stems that have back-seats which are either 
fluid pressure energized or loaded with springs which provide a constant 
seating force and do not automatically self-adjust for wear. 
Therefore, there exists a need today in which rotary valves could be 
provided with back-seats for the stem whereby the back-seating force 
automatically self-adjusts for wear of the seating surfaces independent of 
fluid pressure. 
Prior art Blevans U.S. Pat. No. 2,719,022 of Sep. 27, 1955 does show a 
rotary valve in which the stem passageway is sealed from the valve body 
cavity. But this sealing is not effective because of stem back-seating and 
the sealing force is not automatically externally variable. The sealing of 
the stem passageway is caused by plastic packing injected under pressure 
around the outer periphery of a stem sealing ring located in the valve 
body around the stem in the stem passageway. This method is not foolproof 
by any means. The method is not a positive way to seal the stem passageway 
from the valve body cavity. The sealing integrity around the stem will be 
compromised, if there is a drop in the pressure of the injected plastic 
packing material and this is bound to happen sooner or later. Secondly, 
there is no automatic self-adjustment for wear of the seating surfaces. 
Also the plastic packing will have to be injected under such a high 
pressure that resistance to stem rotation will be encountered. Blevans 
rotary valve is extremely complex and expensive for manufacture and 
sealing around the stem in the stem passageway cannot be assured. 
Prior art Gray U.S. Pat. No. 2,124,334 shows a gate valve wherein the stem 
is back-seated in both opened and closed positions of the valve. However, 
Gray U.S. Pat. No. 2,124,334 applies to a reciprocating gate valve wherein 
the closure member reciprocates between open and closed positions of the 
valve. Also during Gray's times there was no pressing need for the 
prevention of fugitive emissions. The instant patent application refers to 
rotary valves only in which the closure member rotates during open and 
closed positions of the valve. 
BRIEF DESCRIPTION OF THE PRESENT INVENTION 
This invention is concerned with prevention of fugitive emission associated 
with leakage around the valve stem of a rotary valve. The fugitive 
emission is prevented, rather than contained, by isolating the stem 
packing from the fluid in the valve body cavity and is achieved by 
providing a back-seat on the stem which seals the stem passageway from the 
valve body cavity. The back-seat on the stem is located just below the 
stuffing box , that is between the stem packing and the valve body cavity. 
The stem back-seat is mechanically loaded with automatically 
self-adjusting seating force that is externally variable. 
A rotary valve comprising a valve body cavity and a fluid flow passageway 
therethrough intersecting the valve body cavity, has a stem passageway in 
communication with the valve body cavity. A flow control member is 
disposed in the valve body cavity for selectively closing or opening the 
fluid flow passageway. A valve operator is connected to the flow control 
member for selectively moving the flow control member to a flow closed 
position or to a flow open position. The valve operator consists of a 
movable stem that reciprocates in the stem passageway and is connected to 
the flow control member so that when the stem rotates, the flow control 
member rotates with the stem. 
The stem passageway has a stem seating surface surrounding the stem 
passageway. The stem has a stem sealing surface disposed around the stem 
complementary to and facing the stem seating surface surrounding the stem 
passageway. When the stem sealing surface is forced against the stem 
seating surface by the valve operator, the stem sealing surface sealingly 
engages the stem seating surface and thus prevents fluid in the valve body 
cavity from communicating with the stem packing located above the stem 
seating surface. The stem seating surface is located between the stem 
packing and the valve body cavity. The valve operator provides the 
externally variable seating force needed to achieve effective sealing at 
the stem back-seat. The valve operator automatically self-adjusts the stem 
seating force as needed. 
When the valve operator is moved in one direction, the stem sealing surface 
moves a limited extent away from the stem seating surface just enough to 
facilitate stem rotation, the stem then rotates with the flow control 
member through a predetermined interval of rotation. Continued further 
movement of the valve operator in the same direction causes the stem 
sealing surface to move along the stem axis towards the stem seating 
surface to sealingly engage the stem seating surface. Thus the stem 
passageway is sealed from the valve body cavity. This sequence of stem 
movement of unseating, turning and reseating the stem is generally called 
"Lift-Turn-and-Reseat" means. 
The "Lift-Turn-and-Reseat" sequence of stem movement is repeated when the 
valve operator is moved in the opposite direction to selectively close or 
open the fluid flow passageway. Thus the stem passageway is sealed from 
the valve body cavity when the flow control member is in flow closed 
position as well as in flow open position. When the stem sealing surface 
moves a limited extent away from the stem seating surface to facilitate 
stem rotation, some little quantity of fluid might escape from the valve 
body cavity to the stem packing which provides a back-up seal for the very 
short duration during the stem rotation until the stem is reseated onto 
the stem seating surface. This type of back-seating of the rotary stem 
with just above described "Lift-Turn-and-Reseat" type stem movement is 
useful particularly for Ball, Butterfly and Plug types of rotary valves 
for preventing fugitive emissions of hazardous chemicals. 
In some rotary valves, the stem passageway is not required to be sealed in 
the fluid flow closed position, particularly when the valve remains closed 
for very short periods and remains in fluid flow open position most of the 
time. In such instances, another sequence of stem movement called 
"Lift-and-Turn" is adopted to seal the stem passageway in the valve open 
position. "Lift-and-Turn" sequence is really a partial sequence of 
"Lift-Turn-and-Reseat" means. When the valve operator is moved in one 
direction, the stem sealing surface moves a limited extent away from the 
stem seating surface along the stem axis to facilitate stem rotation. With 
continued further movement of the valve operator in the same direction, 
the stem rotates together with the flow control member through a 
predetermined interval of rotation to close the fluid flow passageway. 
When the valve operator is moved in the opposite direction, the said 
sequence of stem movement is reversed. That is, first the stem rotates 
together with the flow control member through a pre-determined interval of 
rotation and then the stem reseats on the stem seating surface to 
sealingly close the stem passageway from the valve body cavity. 
In the present invention, the stem passageway is sealed and unsealed by the 
reciprocating movement of the stem caused by the valve operator, and the 
sealing of the stem passageway does not depend on the fluid pressure in 
the valve body cavity. However, fluid pressure in the valve body cavity 
aids in the sealing function. The valve operator reciprocates the stem and 
provides the automatic externally variable stem seating force needed to 
maintain effective sealing of the stem passageway. 
"Lift-and-Turn" means and "Lift-Turn-and-Reseat" means are mechanisms by 
which a rotary valve stem is reciprocated along the stem axis followed by 
rotary motion of the stem. Some "Lift-and-Turn" means are taught in prior 
art of Heggem U.S. Pat. No. 2,076,841/Hodgeman et al U.S. Pat. No. 
4,234,157/Hilker U.S. Pat. No. 2,383,549/Nevrekar U.S. Pat. No. 5,205,535. 
Some "Lift-Turn-and-Reseat" means are taught in prior art of Reed U.S. 
Pat. No. 2,392,880 and Snyder U.S. Pat. No. 2,443,995. 
The phrases "Lift-and-Turn" and "Lift-Turn-and-Reseat" means are normally 
used as applied to unseating and reseating of a rotary valve closure 
member onto the valve body seats surrounding the fluid flow passageway. 
The instant invention teaches new uses for the "Lift-and-Turn" means and 
"Lift-Turn-and-Reseat" means. The new uses refer to unseating and 
reseating of the rotary valve stem, rather than the closure member, the 
sequence of motion being very similar. 
"Lift-and-Turn" and "Lift-Turn-and-Reseat" means refer to the stem sealing 
surface being lifted off--moving away from, the stem seating surface. The 
stem sealing surface needs to be lifted off the stem seating surface just 
enough to facilitate stem rotation along with the flow control member. 
This lifting of the stem is generally very small, just enough to relieve 
stem seat load to facilitate stem rotation with less torque of the valve 
operator. The lifting of the stem is required to reduce the valve operator 
torque that is needed to rotate the flow control member, so that the valve 
operator size can be kept small. The valve operator needs torque to 
overcome resistance to rotation of the flow control member and also to 
overcome resistance to rotation of the stem at the stem seating surface in 
the stem passageway. By lifting the stem sealing surface off the stem 
seating surface before stem rotation, the torque required to overcome 
resistance to stem rotation at the stem seat can be greatly reduced. 
The lifting and reseating of the stem occurs when the stem reciprocates 
along the stem passageway. The flow control member is connected to the 
stem. In rotary valves of the type where the flow control member cannot 
reciprocate together with the stem, such as a ball valve or a butterfly 
valve for example, a flexible connection between the stem and the flow 
control member is called for, whereby the stem can reciprocate relative to 
the flow control member. In a floating ball valve, this flexible 
connection already exists in the form of a tongue at the end of the stem 
sliding in a groove on the ball. The reciprocating movement of the stem 
tongue inside the ball groove is very small--just enough to relieve stem 
seat load to facilitate stem rotation. In a rotary cylindrical plug valve 
with floating side segments or slips, the middle plug can reciprocate with 
the stem. In a rotary tapered plug valve, the tapered plug can reciprocate 
with the stem also. Therefore, in a tapered plug valve and in a 
cylindrical plug valve with side segments, the "Lift-and-Turn" means can 
be successfully used to seal the stem passageway in the valve open 
position. 
The instant invention is a very simple concept. The concept teaches that a 
rotary valve stem is back-seated to seal the stem passageway from the 
valve body cavity, and the valve operator provides the necessary automatic 
externally variable stem force required to seal the stem passageway. Until 
now, a "Lift-and-Turn" means is used for lifting the closure member off 
the valve body seats, and live loading of stem packing is used to contain 
fugitive emission. However, this invention is a NEW USE concept for the 
"Lift-and-Turn" means--to PREVENT fugitive emission, not just to contain 
it--and a novel concept at that. 
In summary, the invention consists of providing a back-seat for a rotary 
valve stem to sealingly close the stem passageway from the valve body 
cavity, valve operator means to reciprocate the stem, and valve operator 
means for rotating the stem together with the flow control means, the said 
valve operator means providing the externally variable stem force that 
automatically self-adjusts to sealingly close the stem passageway. 
An object of the present invention is to isolate the stem packing of a 
rotary valve from the fluid in the valve body cavity. 
Another object of the present invention is to provide for sealing of the 
stem passageway of a rotary valve stem from the fluid in the valve body 
cavity. 
Another object of the present invention is to prevent fugitive emissions 
caused by leakage around stem of rotary valves. 
Still another object of the present invention is to prolong the life of 
stem packing of rotary valves. 
Other objects and advantages of the present invention will become apparent 
as the following detailed description of the invention is read in 
conjunction with the accompanying drawings and the appended claims.

DETAILED DESCRIPTION 
With reference to FIG. 1, the rotary ball valve assembly 100 is shown as 
constructed in accordance with features of the present invention. 
A valve body 110 includes fluid flow passageways 112 and 114 on opposite 
sides of the valve body cavity 116. The valve body cavity 116 is open to 
the fluid flow passageways 112 and 114, and also opens upwardly to one 
side of the valve body 110 to communicate with the bonnet 142. 
A flow control member 118 is disposed in the cavity 116 to open or close 
the fluid flow passageways 112-114. The flow control member 118 comprises 
a floating ball closure member 119 with a fluid flow conduit 113 
therethrough alignable with the fluid flow passageways 112-114. Two 
sealing rings 134 and 136 are disposed in the valve body 110 surrounding 
the fluid flow passageways 112, 114 to sealingly engage the ball closure 
member 119. 
The ball closure member 119 is rotated by a valve operator 150 which 
comprises a stem 120 that passes through the stem passageway 121 in the 
bonnet 142. The stem passageway 121 communicates with the body cavity 116 
and has a stem seating ring 132 disposed in the recess 133 surrounding the 
stem passageway 121. The upper end 123 of the stem 120 is connected to the 
valve operator 150 through a lift-turn-and-reseat mechanism 152 by which 
the stem 120 is reciprocated and rotated. The lower end 125 of the stem 
120 passes through the stem passageway 121 and has a narrow tongue 124 
that protrudes into an elongated groove 126 in the ball closure member 
119. The depth of the groove 126 is more than the length of the tongue 124 
so that the tongue 124 can reciprocate in the groove 126 to a limited 
extent. The tongue 124 is slidingly connected to the ball closure member 
119 so that when the stem 120 rotates, the ball closure member 119 rotates 
with the stem. The lower end 125 of the stem 120 has an enlarged portion 
with a collar 122 which has a sealing surface 128 complementary to and 
facing the stem seating surface 130 on the stem seating ring 132. The stem 
sealing surface 128 sealingly engages the stem seating surface 130 
surrounding the stem passageway 121 when the ball valve is in flow closed 
or in flow open position. The elongated groove 126 is positioned relative 
to the axis of the conduit 113 so that the floating ball 119 is free to be 
pushed to the downstream sealing ring in the valve body by fluid pressure 
in the valve closed position. 
A packing gland 138 exerts compressive force on the stem packing 140 
surrounding the stem 120. The stem packing 140 in turn exerts radial 
thrust around the stem 120 to effect sealing engagement therewith around 
the stem periphery in order to stop leakage of fluid from the valve body 
cavity. The ball valve is shown in open position in FIG. 1. When the valve 
operator 150 moves in one direction to close the valve, the stem 120 moves 
down a limited extent towards the ball closure member, the groove 126 in 
the ball accommodating this stem movement. The downward movement of the 
stem 120 causes the sealing surface 128 to move away from the stem seating 
surface 130 thereby relieving stem seating load on the seating surface 130 
and facilitates stem rotation with less effort by the valve operator. With 
further movement of the valve operator 150 in the same direction, the stem 
120 rotates together with the ball closure member 119 through a 
pre-determined interval of rotation, in this case 90 degrees, to close the 
fluid flow passageway 112-114 on the downstream side. With continued 
further movement of the valve operator in the same direction, the stem 120 
moves in the opposite direction towards the stem seating surface 130 until 
the stem sealing surface 128 sealingly engages the stem seating surface 
130 thereby sealing the stem passageway 121 from the valve body cavity 
116. This sequence of stem movement of unseating, turning and reseating 
the stem is produced by the lift-turn-and-reseat mechanism 152 referred to 
earlier. 
When the valve operator is moved in the opposite direction to open the ball 
valve, the said sequence of stem movement is repeated. That is, the stem 
120 moves down to relieve stem seat load at stem seating surface 130, 
rotates through 90 degrees together with the ball closure member 119 and 
then the stem 120 moves up until the stem sealing surface 128 sealingly 
engages the stem seating surface 130 to seal the stem passageway 121 from 
the valve body cavity 116 in the valve open position. Thus, the stem 
passageway 121 is sealed from the valve body cavity 116 when the valve is 
in fluid flow closed as well as in fluid flow open position. This sealing 
is achieved by using the lift-turn-and-reseat mechanism 152 for the stem 
movement during the opening and closing movement of the valve operator 
150, and the stem packing 140 is isolated from the fluid in the valve body 
cavity 116. Fugitive emissions caused by leakage around the stem are 
therefore prevented. This also increases the life of the stem packing 140. 
The automatically externally variable seating force needed for stem 
sealing is provided by the valve operator 150 through the 
lift-turn-and-reseat mechanism 152. 
Any generic lift-turn-and-reseat mechanism can be used by which the stem is 
unseated, rotated and then reseated in order to seal the stem passageway. 
In FIG. 1, the lift-turn-and-reseat mechanism 152 that is shown, is 
constructed similar to the one disclosed in U.S. Pat. No. 2,392,880, Jan. 
15, 1946 by I. N. Reed which is designed for unseating and reseating a 
tapered plug onto the valve body seats. 
The bonnet 142 extends into a yoke 154 to house the packing gland 138. The 
yoke 154 supports a housing 156 inside which is disposed the 
lift-turn-and-reseat mechanism 152 which consists of a cage 158 that is 
connected to the upper end 123 of the stem 120 by means of a cross pin 
160. An operative screw 162 with separated external threads 164 
(left-hand) and 166 (right-hand), is journaled at 168 in the cage 158. The 
screws 164, 166 co-act with complementary internally threaded collars 172, 
174 respectively. The collars 172, 174 have diametrically opposed pins 170 
which protrude through the elongated slots 176 opposite each other and 
formed in the walls of the cage 158. The slots 176 are parallel to the 
operating screw 162 axis. For facilitating assembly, the pins 170 are 
screwed into the collars 172, 174. 
The ends of the pins 170 are guided in spirally disposed grooves 178, 180 
formed in the housing 156. FIG. 1A shows the disposition of the grooves 
178, 180 when looked in the direction of arrow "A" towards the housing 
156. The grooves 178, 180 have small vertical portions 182, 184 and 
inclined portions 186, 188 respectively. FIG. 1A shows the position of the 
pins 170 in the valve open position, when the stem sealing surface 128 
sealingly engages the stem seating surface 130. When the valve operator 
150 is turned in one direction to close the valve--in this case clockwise 
looking from top, the operating screw 162 rotates clockwise. The lower pin 
170 being at the end of the groove 180, cannot move down. Therefore the 
operating screw 164 pushes the collar 172 down along the vertical portion 
182 of the groove 178, and this in turn pushes the whole stem 120 down so 
that the sealing surface 128 moves away from the seating surface 130. With 
further movement of the valve operator in the same direction, the pins 170 
are forced to travel along the inclined portions 186, 188 of the grooves 
178, 180 respectively, until the pins 170 reach the end of the inclined 
portions of the grooves. The guided movement of the pins 170 along the 
inclined portions of the grooves 178, 180, forces the cage 158 to rotate 
through a like angle, which again causes the stem 120 and the ball closure 
member 119, to rotate through a like angle, in this case 90 degrees. With 
continued rotation of the valve operator 150 in the same direction, the 
upper pin 170 cannot travel further. The operating screw thread 166 
therefore pushes the lower collar 174 upwards along the vertical portion 
184 of the groove 180. This in turn pushes the stem 120 upwards so that 
the sealing surface 128 sealingly engages the seating surface 130 when the 
valve is in fluid flow closed position. When the valve operator 150 is 
moved in the opposite direction, in this case counterclockwise looking 
from top, the sequence of stem movement is repeated--namely, the stem 120 
lifts off the stem seating surface 130, rotates through 90 degrees and 
then reseats onto the stem seating surface 130 to seal the stem passageway 
121 from the valve body cavity 116. 
The two grooves 178 and 180 together with their respective threaded collars 
172 and 174 represent a "lift-turn-and-reseat" mechanism by which the stem 
is unseated, rotated and reseated onto the same seat when the valve 
operator is moved in one direction. The sequence is repeated when the 
valve operator is moved in the opposite direction. However, each of the 
grooves 178 and 180 individually represents a "lift-and-turn" mechanism by 
which the stem is unseated and rotated when the valve operator is moved in 
one direction, and the sequence of stem movement is reversed when the 
valve operator is moved in the opposite direction. 
FIG. 2 shows another embodiment of the rotary ball valve assembly 200 which 
has features of the present invention. Since FIG. 2 is very similar to 
FIG. 1, for the sake of brevity, only important features will be 
described. FIG. 2 shows a novel construction of the stem by which the stem 
passageway is sealed in the valve open and in the valve closed position by 
a "lift-and-turn" mechanism represented by a single groove 278 together 
with a threaded collar 272. FIG. 2A shows the disposition of the groove 
278 as seen in the direction of arrow "A". The groove 278 consists of two 
vertical portions 282, 284 connected by an inclined portion 286. As in 
FIG. 1, the stem passageway carries a seat ring 232. A second seat ring 
231 is placed below the first seat ring 232 but in opposite configuration. 
The stem has two sealing surfaces oppositely disposed to each other to 
co-act with the corresponding seat rings 232,231. The valve is shown in 
open position with the stem passageway sealed at the upper seat ring 232. 
A sturdy clamping plate 241 is screwed into the bonnet 242 to hold the 
seat rings 232, 231 in place. When the valve operator is moved in one 
direction to close the valve, the stem is lifted off the first seat ring 
232, rotated 90 degrees and with further movement of the valve operator in 
the same direction, the stem seats on the lower seat ring 231 to seal the 
stem passageway in the valve closed position. When the valve operator is 
moved in the opposite direction to open the valve, the stem is lifted off 
the lower seat ring 231, rotated 90 degrees and with further movement of 
the valve operator in the same direction, the stem seats on the upper seat 
ring 232 to sealingly close the stem passageway from the valve body 
cavity. Thus the stem passageway is sealed from the valve body cavity by 
the movement of the valve operator in both directions by the 
"lift-and-turn" mechanism represented by a single groove. It should be 
clearly understood here that the seat rings 232, 231 can be suitably 
placed anywhere along the stem passageway, and not necessarily at the 
bottom of the stem passageway as shown in FIG. 2. Also, the left-hand 
threaded collar 272 can be replaced by a right-hand threaded collar with 
the corresponding mirror image groove of groove 278. The grooves can be 
constructed with different combinations of vertical, inclined and 
horizontal portions to obtain a desired sequence of stem movement, and 
this will be apparent to anyone skilled in the art. 
In FIGS. 1 and 2, the Lift-and-Turn means shown are as taught in Reed U.S. 
Pat. No. 2,392,880. There are many other variations of Lift-and-Turn means 
that can be used for the instant invention. Nevrekar U.S. Pat. No. 
5,205,535 shows a lift-and-turn mechanism that is spring activated and can 
also be used on the instant invention, although it may not be obvious to 
those skilled in the art. 
From the above description it is clear that the present invention is well 
adapted to carry out the objects and to attain the ends and advantages 
mentioned herein as well as those inherent in the invention. While 
presently preferred embodiment has been described for purposes of this 
disclosure, it will be understood that numerous changes may be made which 
will readily suggest themselves to those skilled in the art and which are 
accomplished within the spirit of the invention disclosed and as defined 
in the appended claims.