Seal for turning valve bodies, in particular for valves in nuclear-engineering plants

The seal for turning valve bodies, in particular for valves in radioactive lants, is composed of a molded element of flexible graphite which is coated with a thin, flexible tantalum layer. The tantalum enclosure surrounds the graphite molded element, preferably all around. The tantalum layer is sufficiently thin so that it remains flexible.

The present invention relates generally to a seal for turning valve bodies 
and more particularly to valves used in nuclear-engineering plants. 
From DE-OS No. 2,748,135 it is known to use a flexible graphite laminate as 
one of the materials for sealings and packings, whereby the laminate is 
applied to other materials for example a suitable metal. DE-OS No. 
2,612,296 and DEP No. 2,039,355 also describe the use of flexible graphite 
material in the fabrication of seals. 
Flexible graphite materials are generally known according to the state of 
the art and are described, in addition to the aforecited publications, in 
DE-OS No. 2,855,408 and DE-OS No. 3,117,567. The essential advantages of 
flexible graphite materials may be found in the following properties: 
The materials are liquid- and gas-tight: 
they are highly temperature-resistant; 
they are resistant to radiation; 
They are resistant to most chemicals; and 
they have great flexibility and good elasticity and, in some applications, 
they also act as a self-lubricating seal 
The latter property, however, is coupled with the disadvantage that in a 
frequently actuated valve, the graphite material is relatively quickly 
worn off. In general terms, the useful life of such a seal is relatively 
short. In valves employed in radioactive plants, e.g., in plants for the 
reprocessing of nuclear fuel, the useful life of the valve is of special 
importance inasmuch as the replacement of worn-off parts in radioactive 
plants is very costly because the operation of the plant must be 
temporarily stopped, which naturally is extremely undesirable. 
Sealing materials of polytetrafluoroethylene plastics have not been found 
satisfactory since PTFE, even though chemically one of the most stable 
plastics, has very low radiation resistance and also has little 
resilience. In addition, various copolymers have been developed but their 
chemical stability, however, is small. For these reasons, it may be said 
that for the fluidized currents of the Purex process, no plastics are 
available for seals with a calculable useful life. 
It is the purpose of the invention to improve the seal of the type 
described in such a manner that its useful life is increased. 
This purpose is attained by the distinguishing features indicated in the 
appended claims. Advantageous embodiments and further refinements of the 
invention also become apparent from the appended claims. 
In short, in accordance with the present invention, the seal composed of 
flexible graphite materials is coated with a thin, flexible layer of 
tantalum. Tantalum has excellent ductility which is highly desirable for 
the intended purpose. Tantalum also has very good sliding or lowfriction 
properties so that a seizing or jamming of the valve body does not occur. 
In acccordance with the present invention, the tantalum coating layer is 
sufficiently thin to remain flexible so that the good flexibilty 
properties of the graphite covered by tantalum are preserved. 
It should also be stressed that the seal according to the present invention 
is likewise well suited for chemical plants in that tantalum is chemically 
very stable.

In FIG. 1, the housing and, respectively, the mounting of a valve is 
indicated schematically by the reference character -1-. The housing -1- 
has an inlet opening -2- and an outlet opening -3- whereby the flow path 
can be closed off by a valve cone -4-. The valve cone -4- is provided with 
a passage opening -5- situated in the flow path and effecting an opening 
or closing of the valve by turning of the valve cone about its own 
longitudinal axis. 
Over the valve cone -4- is slid a molded element -6- in the shape of a 
conical cylinder which is provided on either side with recesses -11- (FIG. 
3) opposite the passage opening -5-. 
The molded element -6- is composed of flexible graphite which, in turn, is 
coated with a thin, flexible layer of tantalum. The tantalum layer is 
sufficiently thin so that the flexiblity properties of the graphite are 
not impaired. The flexible graphite layer may also be built-up of a 
plurality of thin layers laminated one on top of the other. Cut-outs may 
be provided in thin, laminated layers of flexible graphite in defined 
locations in order to create relief surfaces for a more balanced pressure 
distribution. 
From FIGS. 2 to 4 it becomes clear that the tantalum coating is of composed 
an inner tantalum sleeve -7- and an outer tantalum sleeve -8- which, 
between them, enclose the graphite molded element -6-. At the end faces, 
and also additionally in the region of the recess -11-, there are provided 
tantalum covers -9- which, in sections, are placed between the sleeves -7- 
and as well as over the end face of the molded element -6-. Complete 
sealing is obtained because the covers -9- are welded (at -10-) together 
with the inner and outer sleeves -7- and -8-. Advantageously, all welding 
seams -10- are produced by the precisely focusable electron beam welding 
process, known in itself. The sealing of the recesses -11- opposite the 
passage openings -5- is obtained in the same manner as the sealing of the 
end faces as shown in FIG. 2. Thus, the graphite molded element -6- is 
hermitically encapsulated within a thin tantalum enclosure. The molded 
element -6- encapsulated in this manner is fixed on the valve cone -4- by 
means of a frame-like holding device -12-. Thereby is thus obtained a 
fixing of the molded element -6- in both the axial direction and the 
direction of turning. Around the passage openings -5- arranged on either 
side of the valve cone -4- extends a groove -13- into which is inserted 
the frame-like holding device -12-. Securing thereof is obtained by a 
press fit. In the embodiment illustrated, the passage openings -5- and 
holding device -12- appear rectangular in plan view. Evidently, circular, 
oval or other openings may be provided. 
In the exemplifying embodiment shown in FIG. 2, the end face cover -9- is 
flanged so that it overlaps the graphite molded element -6-. In the 
embodiment illustrated in FIG. 4, however, the covers are annular disks or 
rings which without any overlapping are welded to the sleeves -7- and -8- 
at the welds -10-. 
In the embodiment represented in FIG. 1 there is also shown in greater 
detail the arrangement of the valve connected with the seal according to 
the present invention. At its smaller diameter front end, the valve cone 
-4- is provided with a cylindrical section -15- which penetrates a 
cylindrical housing opening -20- (!). Starting from the inlet and outlet 
openings -2- and -3-, respectively, housing -1- is provided, in the region 
of the front end of the valve cone -4- with a first conical valve seat 
-17- in which is guided the molded element -6- of the seal in accordance 
with the present invention. This is followed, by way of a transverse step 
or shoulder step -18-, by a second conical valve seat -19- with a smaller 
diameter, the second diameter corresponding approximately to the diameter 
there of the valve cone -4-. Thereafter follows a further step or 
transverse shoulder -20- and, successively, a cylindrical housing recess 
-21-. 
On the other side of the valve cone -4- there is also provided a conical 
valve seat -22- in which is guided the other end of the seal. This is 
followed by a cylindrical opening -23- of the housing -1- whose diameter 
is larger (by approximately the wall thickness of the seal -6-) than the 
diameter of the rear cylindrical portion -16- of the valve cone -4- with 
the seal mounted on it can slide axially (from the right to the left as 
shown in FIG. 1). 
A preferred field of application of the present invention is as a seal for 
cone valves in the fluidized currents of the Purex process whereby the 
operational components are comprised of radiation-resistant, flexible and 
corrosion-resistant materials. By means of the seal according to the 
present invention there can be achieved a definite increase in service 
life and also increased maintenance and replacement intervals. 
Another preferred filed of application of the present invention is the 
utilization of the seal in chemical plants, e.g., in case of chemicals 
which do not attack tantalum. In HNO.sub.3 and many other chemicals, 
tantalum is an absolutely corrosion-resistant material. In contrast to 
plastics, the flexible graphite enclosed by tantalum retains its 
characteristics, even at temperatures exceeding 150.degree. C. It does not 
liquefy and does not change chemically, even on inclusion in tantalum. 
All technical details contained in the patent claims, the description and 
the drawing are essential parts of the invention, each by itself and also 
in any combination whatever.