Valve stem packing

A valve stem packing assembly in the form of a stacked array of seal ring elements of generally V-shaped cross-sectional configuration, a plurality of backup-energizing rings of generally Y-shaped cross-sectional configuration interspersed between the seal ring elements, a spring-energized U-shaped lip seal ring adjacent one end of the array, and a T-shaped adapter ring adjacent the other end of the array.

This invention relates generally to fluid seals, and more particularly to 
packings for providing a high pressure fluid seal between a valve stem and 
bonnet or other element surrounding the stem. 
BACKGROUND 
Although valve stem packings constructed of elastomeric materials are known 
to be satisfactory for a variety of conditions, such packings do not 
provide the desired sealing function when subjected to high pressure gas 
environments, their failure being due to the phenomenon known as 
"explosive decompression". Replacing elastomeric materials with 
non-elastomers eliminates the "explosive decompression" problem, but 
non-elastomers creep when subjected to pressure and then do not return to 
their original condition when the pressure is removed, i.e., they have no 
memory. Due to the creep problem and the difference in the coefficient of 
thermal expansion of non-elastomers and the metallic packing gland and 
stem of a valve conventional non-elastomeric stem packings leak after 
subjection to a pressure and temperature cycle. 
In attempts to overcome the foregoing problems non-elastomeric lip seals 
having been provided with spring energizers to bias the sealing lips 
against the opposing metallic surface. Such a design is effective where 
the metallic surface is very smooth, but if the sealing lip is scratched 
or otherwise slightly damaged it will leak. Spring energized seals cannot 
be stacked in series to increase reliability unless a cartridge or other 
carrier is provided to contain them, but the carrier constitutes an 
undesirable additional part that adds to the cost, creates another 
potential leak path in the system, and necessitates enlargement of the 
packing gland and packing chamber. 
SUMMARY OF THE INVENTION 
The foregoing and other problems are solved by the present invention which, 
broadly considered, is embodied in a valve stem packing comprising a 
stacked assembly of V-ring seal elements, special backup energizing rings 
interspersed between the seal elements, and a spring-energized lip seal 
ring that is retained in functional positions by an adapter ring having a 
generally tee-shaped cross-sectional configuration. As the assembly is 
installed in a valve stem packing chamber with the T-adapter ring at one 
end of the assembly and a backup ring for the V-ring seal elements at the 
other end, the lip seal ring and the V-ring seal elements are radially 
compressed to establish an initial seal between the stem and the chamber 
wall. When the assembly is subjected to interval valve pressure the V-ring 
seal elements and the lip seal ring are additionally compressed and 
deformed to fill annular spaces that may still exist between the seal 
elements, their backup/energizing rings and the lip seal ring, thereby 
establishing an essentially void-free dynamic packing between the stem and 
the chamber wall that is capable of withstanding many hundreds of gate 
valve stroke cycles (valve open to closed to open constituting one cycle) 
at unusually high pressures of fifteen thousand pounds per square inch and 
above, and unusually high temperatures of two-hundred and fifty degrees 
Farenheit and above. Furthermore, a stem packing assembly according to the 
present invention is extrusion-free, insensitive to fluctuations in 
pressure and/or temperature, and exceedingly resistant to chemical attack.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In accordance with the present invention, and as illustrated in FIG. 1 of 
the drawings, a valve stem packing assembly 10 can be employed in a rising 
stem gate valve 12 to provide a high pressure, high temperature dynamic 
seal between the valve's stem 14 and bonnet 16. In the valve 12 the 
packing assembly 10 is located in, and confined to, a packing chamber 18 
in the bonnet 16, and a packing gland nut 20 retains the packing assembly 
10 in functional position in the chamber 18. The valve 12 further includes 
a body 22 to which the bonnet 16 is removably secured by a threaded 
retainer sleeve 24, and a gate element 26 connected to the stem 14 for 
translatory longitudinal movement between its illustrated upper or "valve 
open" position and its lower or "valve closed" position (not shown) 
wherein it blocks the flow, represented by arrow 28, through the valve. In 
the conventional manner the gate 26 is suitably connected to the stem 14 
so that it is raised and lowered with the stem when a handwheel 30, or 
other suitable means of operating the valve, is actuated. 
As seen more clearly in FIGS. 2-4, the packing assembly 10 comprises a 
plurality of V-ring seal elements in stacked array and oriented in an 
inverted attitude toward the valve gate 26, a like plurality of somewhat 
Y-shaped special backup/energizing rings 34 inverted and interspersed 
between and beneath the V-ring seal elements 32, a spring-energized lip 
seal ring 36 beneath the lowermost backup/energizing ring 34a, a lower 
adapter ring 38 having cross-sectional configuration generally resembling 
an inverted tee, and an upper adapter ring 40 with an inverted vee-shaped 
lower wall 40a that provides a backup function to the adjacent V-ring 32, 
a retaining function, in cooperation with the packing gland nut 20 and a 
spacer ring 42 (FIGS. 3 and 4), that prevents the packing assembly 10 from 
moving out of proper position in the chamber 19 during translation of the 
valve gate 26 from closed to open position, and also acts as a guide 
bearing for the valve item 14. 
The preferred composition from which the V-ring seal elements 32 and the 
lip seal ring 36 are made is polytetrafluoroethylene (PTFE) filled with 
glass (fifteen percent), and molybdenum disulfide (five percent), and the 
special backup/energizing rings 34 preferably are composed of PTFE filled 
with carbon graphite (twenty-five percent). In order to preserve the 
functional integrity of the lip seal ring's U-shaped energizing spring 44, 
that spring preferably is constructed from a NACE (National Association of 
Corrosion Engineers)-approved metal such as, for example, ELGILOY which is 
a metallic alloy product of the Welby Clock Division of Elgin National 
Industries. With respect to the upper and lower adapter rings 40, 38, 
their preferred composition is glass-filled PEEK (polyetheretherketone) 
containing forty percent glass and two and one-half to five percent PPS 
(polyphenylenesulfide). 
As shown in FIG. 2, the surfaces 32b of the V-ring seal elements 32 define 
an angle, with respect to the vertical, or greater magnitude than that 
defined by the opposed surfaces 34b of the backup/energizing rings 34, 
thereby establishing relatively small annular spaces or voids 50 between 
the elements 32 and rings 34 before the assembly 10 is installed in the 
packing chamber 18. Similarly, prior to installation the opposed surfaces 
32c, 34c of the elements 32 and rings 34, respectively, define different 
angles with respect to the vertical, thereby also defining small annular 
spaces or voids 52 therebetween. Also as illustrated in FIG. 2, central 
annular spaces or voids 54 exist between the V-ring seal elements 32 and 
the adjacent backup/energizing rings 34, between the uppermost seal 
element 32 and the adaptor ring 40, and between the lowermost 
backup/energizing ring 34 and the lip seal ring 36, before installation of 
the assembly 10 in the valve 12. 
As illustrated in FIG. 3, when the stem packing assembly 10 is installed in 
a properly sized packing chamber 18 surrounding a properly sized valve 
stem 14 the annular spaces or voids 50 and 52 disappear as a result of 
radial compression of the V-ring seal elements 32 and the 
backup/energizing rings 34, whereas the annular spaces or voids 54 remain. 
When installed as shown in FIG. 3, the seal elements 32, backup/energizing 
rings 34 and the adjacent surfaces of the valve bonnet 16 and the valve 
stem 14 define annular spaces or voids 56 of generally triangular shape in 
cross-section. Furthermore, when installed in the valve the lip seal ring 
36 is radially compressed so that the edges 44a of the downwardly-facing 
energizing spring 44 deflect in the direction of the central upstanding 
"leg" 38a of the lower adapter ring 38. 
When the packing assembly 10 is exposed to elevated internal valve pressure 
as shown in FIG. 4, the lips 36a of the lip seal 36 expand radially to 
effect an initial pressure seal with the stem 14 and the packing chamber 
18, thereby facilitating the lip seal to function as a piston that 
transmits an axial force to the backup/energizing rings 34 and the V-ring 
seal elements 32, which force causes these rings and seal elements to 
migrate toward the backup ring 40. This migration causes deflection or 
deformation of the V-ring seal elements 32 which tend to fill the annular 
spaces 54, 56 and thus produce a voidless relationship between the seal 
elements, the backup/energizing rings 34, the lip seal ring 36, the upper 
adapter ring 40, the valve stem 14 and the wall of the packing chamber 18. 
As pressure increases the axial force transmitted to the V-ring sealing 
elements increases, thereby resulting in an increase in the sealing force 
exerted by the V-ring sealing elements against the valve stem and packing 
chamber wall, and providing a fluid-tight, dynamic seal that will 
withstand many hundreds of translatory cycles of the stem, at temperatures 
of at least 250 degrees F. and pressures of at least 15,000 psi. 
Although the best mode contemplated for carrying out the present invention 
has been herein shown and described, it will be apparent that modification 
and variation may be made without departing from what is regarded to be 
the subject matter of the invention.