Low pressure rupture disk and assembly

An improved low pressure reverse buckling rupture disk and assembly are provided. The rupture disk comprises a concave-convex reversible member having a thickness and a configuration such that said member reverses when a predetermined fluid pressure is exerted on the convex side thereof and having one or more reinforcing embossments disposed therein. The rupture disk assembly includes the above-described rupture disk and knife blade means for severing the disk upon its reversal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to safety pressure relief apparatus, and 
more particularly, to an improved low pressure rupture disk and assembly. 
2. Description of the Prior Art 
A variety of safety pressure relief apparatus of the rupture disk type have 
been developed. Generally, such apparatus include a rupturable member 
supported between a pair of complimentary supporting members or flanges 
which are in turn connected to a relief connection in a vessel or system 
containing fluid pressure. When the fluid pressure within the vessel or 
system exceeds the design rupture pressure of the rupture member, rupture 
occurs causing fluid pressure to be relieved from the vessel or system. 
Rupture disk assemblies including concave-convex reverse buckling rupture 
disks have been developed and used heretofore. Such disks have thicknesses 
and configurations such that they reverse when predetermined fluid 
pressures are exerted on the convex sides thereof. Prior to reversal, a 
reverse buckling rupture disk is in compression which allows the operating 
fluid pressure exerted on the disk to be relatively close to the pressure 
at which the disk is designed to reverse. Upon reversal, the disk ruptures 
thereby relieving pressurized fluid from the vessel or system being 
protected. 
In order to prevent the formation of loose pieces upon rupture, reverse 
buckling rupture disk assemblies have heretofore included knife blades 
upon which the disk impales when reversed. One such knife blade assembly 
is described in U.S. Pat. No. 3,294,277 to Wood which is assigned to the 
assignee in the present invention. Another knife blade assembly is 
described in U.S. Pat. No. 4,236,648 to Wood et al., which is also 
assigned to the assignee of this present invention. The disclosures of the 
foregoing patents are incorporated in this description of the present 
invention by reference. 
While the heretofore developed and used reverse buckling rupture disks and 
assemblies have operated successfully in many applications, problems have 
been encountered in their use in some low pressure applications. For 
example, in low pressure applications where vacuum conditions can exist in 
the vessel or system being protected but the reverse buckling rupture disk 
must still reverse and relieve pressure when a positive low pressure is 
exerted thereon, the material from which the disk is formed must be very 
thin, e.g., a 1 inch in diameter reverse buckling rupture disk designed to 
be subjected to vacuum conditions but rupture at a positive pressure below 
about 25 psig must be formed of stainless steel or the like having a 
thickness in the range of from about 1 to about 2 thousandths of an inch. 
As a result of the thin material from which the disk is formed, the 
reverse pressure brought about by the vacuum quickly causes deformation of 
the disk which in turn brings about premature failure or improper 
operation thereof. 
By the present invention, improved low pressure rupture disks and rupture 
disk assemblies are provided wherein the rapid distortion and weakening of 
the disks when subjected to high heat, vacuums or other reverse or cyclic 
pressure conditions are prevented. 
SUMMARY OF THE INVENTION 
An improved low pressure reverse buckling rupture disk is provided 
comprising a concave-convex reversible member having a thickness and a 
configuration such that said member reverses when a predetermined fluid 
pressure is exerted on the convex side thereof. The rupture member 
includes one or more reinforcing embossments disposed therein which impart 
resistance to damage during handling and installation and to distortion 
and weakening when the member is subjected to a vacuum or other reverse or 
cyclic pressure condition. 
In a preferred embodiment the rupture disk includes a plurality of 
embossments which are equally spaced in end-to-end relationship on a 
centrally positioned circular line. 
A rupture disk assembly of the present invention includes the 
above-described rupture disk and a knife blade member positioned adjacent 
to the rupture disk whereby the disk is severed by the knife blade member 
upon the reversal thereof. 
It is, therefore, a general object of the present invention to provide an 
improved low pressure rupture disk and assembly. 
A further object of the present invention is the provision of a low 
pressure reverse buckling rupture disk which has increased resistance to 
distortion and premature failure as a result of heat, reverse pressure or 
other condition to which the disk is exposed. 
Other and further objects, features and advantages of the present invention 
will be readily apparent to those skilled in the art upon a reading of the 
description of preferred embodiments which follows when taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the drawings and particularly to FIGS. 1 and 2, one form 
of the improved low pressure rupture disk of the present invention is 
illustrated and generally designated by the numeral 10. The rupture disk 
10 is comprised of a concave-convex reversible member 12. In the preferred 
form illustrated in FIGS. 1 and 2, the member 12 includes a circular 
concave-convex portion 14 connected to an annular flat flange portion 16. 
As is well understood by those skilled in the art, the rupture disk 10 is 
formed of a material, generally metal, having a thickness and a 
concave-convex configuration such that when a predetermined fluid pressure 
differential is exerted on the rupture disk 10 by way of the convex side 
thereof, the concave-convex portion 14 reverses itself and ruptures. In 
order to prevent fragmentation, the disk is preferably severed by knife 
blades as will be described hereinbelow. 
As mentioned above, in very low pressure applications, the material from 
which the rupture disk 10 is formed must be very thin, e.g., stainless 
steel having a thickness in the range of from about 0.001 inch to about 
0.002 inch. As a result, the rupture disk 10 is highly susceptible to 
damage when being handled and installed, e.g., exposed to high 
temperatures when being welded, and to distortion in operation, any one of 
which can bring about a rapid premature failure of the rupture disk. In 
order to strengthen the rupture disk and to reduce or prevent such damage 
and/or distortion, the concave-convex portion 14 of the rupture disk 10 is 
reinforced by one or more embossments formed therein. In a presently 
preferred embodiment illustrated in FIGS. 1 and 2, the concave-convex 
portion 14 of the rupture disk 10 includes a plurality of embossments 18 
which are equally spaced in end-to-end relationship on a line defining a 
centrally positioned circle in the concave-convex portion 14. The location 
of the circular line on which the embossments are positioned can vary, but 
generally it is positioned about half-way between the periphery of the 
concave-convex portion 14 and the center of the rupture disk 10. 
The embossments -8 are conveniently formed in the rupture disk 10 by 
conventional die stamping equipment. The particular location, length, 
width, height and spacing of the embossments 18 can vary over a wide range 
and are determined by trial and error to provide a reverse buckling 
rupture disk 10 having the desired reversal pressure and strength 
characteristics. 
An example of a reinforced low pressure reverse buckling rupture disk of 
the present invention is formed of stainless steel having a thickness of 
0.00125 inch. The diameter of the concave-convex portion 14 is 1.460 
inches and the concave-convex portion has a crown height, i.e., a height 
from the bottom surface of the disk to the apex of the inside surface of 
the concave-convex portion of 0.335 inch. The annular flat flange portion 
16 connected to the concave-convex portion 14 is 1.750 inch wide. The 
embossments 18 are each 0.180 inch long, 0.030 inch wide and 0.050 inch 
high and are positioned on a centrally positioned circular line having a 
diameter of 1.100 inch. The spacing between the ends of adjacent 
embossments 18 is 0.108 inch. 
The above-described reinforced low pressure rupture disk has resistance to 
damage and will withstand full vacuum and the reverse pressure created 
thereby without distortion. When the force exerted on the rupture disk 10 
changes from vacuum to positive pressure, the rupture disk will reverse 
and rupture at a positive pressure of about 10 psig. The term "reverse 
pressure" is used herein to mean a pressure differential exerted on the 
rupture disk whereby the pressure on the concave side thereof is higher 
than the pressure on the convex side thereof. 
Referring now to FIGS. 3-6, a rupture disk assembly of this invention 
including the rupture disk 10 described above is illustrated and generally 
referred to by the numeral 20. The assembly 20 is comprised of a 
cylindrical inlet support and protection member 22 attached to the annular 
flat flange portion 16 of the rupture disk 10 such as by a continuous weld 
24. The inlet support member 22 is in turn welded or otherwise attached to 
a connection in a vessel or system containing pressurized fluid to be 
protected from over pressure. Positioned adjacent to the concave side of 
the rupture disk 10 and welded thereto by means of the weld 24 is a knife 
blade member 26. The knife blade member 26 has an annular flat flange 
portion 28, a partially circular serrated cutting edge 30 and a 
non-cutting interior edge 32. The annular flat flange portion 28 of the 
knife blade member 26 is of a size corresponding to the size of the 
annular flat flange portion 16 of the rupture disk 10. As best shown in 
FIG. 4, the partially circular serrated cutting edge 30 is positioned 
interiorly of the annular flat flange 16 of the rupture disk 10 whereby 
the transition connection between the concave-convex portion 14 and the 
annular flange portion 16 of the rupture disk 10 is supported thereby. 
Further, the serrations of the cutting edge 30 are formed in the shape of 
triangle-shaped teeth 34 with rounded notches 36 therebetween. The teeth 
34 are preferably inclined toward and into the concave side of the 
concave-convex portion 14 of the rupture disk 10 at an angle in the range 
of from about 30.degree. to about 45.degree. from the plane of the flange 
portion 28. 
The non-cutting interior edge 32 of the knife blade member 26 comprises a 
chord of the circle partially defined by the serrated cutting edge 30. The 
non-cutting edge 32 is defined by an integral channel shaped portion 
formed in the member 26 having a substantially vertical side. 
When the fluid pressure exerted on the convex side of the concave-convex 
portion 14 of the disk 10 reaches a predetermined level, the 
concave-convex portion reverses. Upon reversal, the part of the 
concave-convex portion 14 which reverses into the serrated cutting edge 30 
is severed thereby. The severing of the concave-convex portion 14 
continues until the cut reaches the non-cutting interior edge 32 at which 
point the partially severed part 40 of the concave-convex portion 14 bends 
inwardly about the non-cutting interior edge 32 of the member 26 as shown 
in FIG. 6. The unsevered integral hinge of the concave-convex portion 14 
adjacent the non-cutting interior edge 32 retains the partially severed 
part 40 to prevent it from being carried downstream by the escaping 
pressurized fluids. 
Referring now to FIGS. 7-10, an alternate form of the improved rupture disk 
assembly of the present invention is illustrated and generally designated 
by the numeral 50. The assembly 50 includes a cylindrical inlet support 
and protection member 52 and an outlet support and knife blade member 54 
between which a reverse buckling rupture disk 56 of the present invention 
is clamped by means of a continuous weld 58. The rupture disk 56 includes 
a single continuous embossment 60 defining a centrally positioned circle 
in the concave-convex portion 62 thereof. The concave-convex portion 62 is 
connected to an annular flat flange portion 64 which is seal welded by the 
weld 58 to both the inlet and outlet support members 52 and 54. 
The embossment 60 functions in the same manner as described above in 
connection with the disk 10 to reinforce the rupture disk 56 and prevent 
its deformation, premature failure, etc. Attached within the outlet 
support member 54 of the assembly 50 are a plurality of sharpened blade 
legs 66. The interior ends of the blade legs 66 are connected together and 
the exterior ends are connected to the interior walls of the outlet 
support member 54 such as by welding. When the rupture disk 56 reaches its 
design rupture pressure, the concave-convex portion 62 reverses and is 
severed by the sharpened knife blade legs 66 as shown in FIG. 10. 
Thus the present invention is well adapted to carry out the objects and 
attain the ends and advantages mentioned as well as those inherent 
therein. While numerous changes in the construction and arrangement of 
parts can be made by those skilled in the art, such changes are 
encompassed within the spirit of this invention as defined by the appended 
claims.