Pressure relieving device

A pressure relieving device having a pressure frame including a first portion and a second portion with a rupture disc clamped therebetween. Each frame portion contains a recess on its inner side which terminates at the sealing surface at the end face and serves to receive cutters, spacer discs, and/or terminating blocks.

This Application claims the priority of German Application P 41 40 088.7, 
filed Dec. 5, 1991. 
The invention relates to a pressure relieving device comprising a two-part 
frame wherein the mutually opposite faces (sealing faces) thereof seal 
when joined together. Each frame part contains, on its inner side, a 
recess which terminates at the face, so that, when the frame parts are 
joined together, a channel is formed around the entire circumference of 
the frame. A rupture disc is clamped between the frame parts and the 
recesses on the inner sides of the frame parts are adapted to receive 
cutters, spacer discs, or terminating blocks (hereinafter sometimes called 
blocks). 
BACKGROUND OF THE INVENTION 
Pressure relieving devices comprising rupture discs and holders are known. 
They are usually fitted as prefabricated units in pipelines, vessels, 
reaction apparatus, and similar technical hollow bodies for protection 
against unacceptable pressure changes. The prefabrication of the 
pressure-relieving devices facilitates and speeds up their exchange in 
lines and apparatus and, in addition, ensures that the sensitive rupture 
discs do not suffer any damage due to improper handling, for example when 
being inserted into the holder. 
It is also known to assist the tearing open of the rupture disc by the use 
of a tearing spike or a group of cutters. To ensure reliable bursting of 
the disc, the tearing device is located in the region of the disc center. 
A precise reaction to the given response pressure is achieved by changing 
the distance between the tearing spike or cutter edges and the plane of 
the disc. In a practical embodiment, the tearing device is set on a 
threaded rod. By variation of the distance between the spike or cutter 
edge and plane of the rupture disc, it is also possible to modify the 
pressure relieving device so it responds to other pressures without the 
necessity of changing the rupture disc. Finally, for special applications, 
the group of cutters can be arranged, not only on one side of the rupture 
disc, but on both sides, so that the pressure-relieving device is 
effective in both directions. 
A disadvantage of the known pressure-relieving devices described above is 
that the hollow body surface area closed by the rupture disc is not 
cleared instantaneously around its entire circumference, even if a tearing 
device is used. If, for example, four cutter edges arranged in the form of 
a cross are used, the rupture disc is cut open segmentally. In particular 
in applications in which relief must take place at relatively low 
pressures, the complete tearing open of the rupture disc may be delayed in 
time and the unhindered flow of the medium leaving or entering may be 
impaired. In addition, the prior art mounting of the tearing device on a 
threaded rod is not always satisfactory, because the device is difficult 
to handle. 
SUMMARY OF THE INVENTION 
It is, therefore, the object of the invention to provide a pressure 
relieving device which, when undesired pressure changes occur, clears the 
entire surface area closed by the rupture disc immediately, without the 
advantages of known devices of the same generic type being lost or 
impaired. 
This object is achieved by a pressure relieving device which comprises a 
two-part frame, with a rupture disc clamped between the parts, wherein 
each frame part contains a recess which terminates at the sealing face and 
is adapted to receive a cutter or a block. If a block is used, it 
preferably terminates at the sealing face. 
The invention is distinguished by the fact that the cutter or cutters which 
initiate or assist the tearing open of the rupture disc act around its 
entire circumference. It is therefore not just scratched and initially 
partially split apart when an undesired pressure change occurs, but rather 
is cut out from the device around its entire circumference, so that the 
relief opening is immediately operative over its entire surface area; 
thus, building-up of a flow resistance by the ruptured rupture disc is 
eliminated. The pressure relieving device is simply adaptable to the most 
varied of requirements, responds to overpressure and/or underpressure, and 
is also quite suitable for use in the low pressure ranges. 
A significant feature of the novel pressure relieving device is the recess 
present in one or both of the two frame parts. It extends around the 
entire circumference of each frame part and serves to receive cutters, 
spacer discs, and/or blocks. The cutters, designed in the shape of the 
frame parts, function to cut out the rupture disc. For setting to a 
certain rupture pressure, the distance of the cutters from the plane of 
the rupture disc can be changed simply by inserting spacer discs. This 
dispenses with the complex and adjustment-sensitive device using a 
threaded rod. 
By using cutters in only one frame half, the pressure relieving device is 
effective only in the event of either a pressure increase or a pressure 
decrease. An embodiment of the device according to the invention in which 
both frame parts are provided with cutters can accordingly be used if it 
is intended to avoid both a certain overpressure and a certain 
underpressure. 
In order to prevent the cut-out rupture disc from being carried away by the 
fluid medium and becoming lodged in the relief line, it may be advisable 
to blunt the cutter edge over a small portion of the circumference. Then 
the relief opening is indeed cleared around the entire circumference, but 
the rupture disc is retained in the pressure relieving device by means of 
a tab formed of the circumferential portion which is not cut through. 
If only one frame half is equipped with a cutter, the opposite half is 
provided with a block. It terminates flush with the sealing face and forms 
a flat surface area therewith. Finally, the recesses of both frame parts 
may also be provided with blocks, so that the device according to the 
invention can also be used if, in a specific case, a tearing device is not 
required. 
The plane defined by the cutter edges preferably runs parallel to the plane 
of the rupture disc, i.e. the edges meet the plane at an angle of 
90.degree.. However, depending on the application, it may be expedient to 
incline the plane of the cutter edges with respect to the plane of the 
rupture disc, so that the angle between plane and cutter edge is greater 
than or less than 90.degree.. 
The rupture disc is clamped between the frame parts. The clamping is 
performed in a known way, for example with the aid of a number of 
screwbolts which are circumferentially disposed at intervals on the frame. 
Rupture discs of the most diverse types and of all materials which are 
usually used for the production of such discs can be used in the novel 
pressure relieving device. If appropriate, allowance can be made for the 
different materials by selection of the cutters, for example with regard 
to material or inclination of the cutter edge. 
In an extreme case, cutting fails to take place due to the material of the 
disc bulging and creeping over the cutter edge. To overcome the problem, 
it has proved particularly successful to provide the rupture discs, 
especially those of plastic, with a predetermined weakened breaking point 
adjacent the periphery of the cutter or cutters. This measure ensures 
that, on contact of the disc by the cutter, the cutting operation is 
performed instantaneously and is not delayed. The predetermined weakened 
breaking point may be impressed in the rupture disc already during 
production; however, it is preferably produced by the cutter itself after 
fitting it into the pressure relieving device.

As can be seen in FIG. 4, the pressure relieving device according to the 
invention comprises frame 1, in which rupture disc 2 is clamped by 
screwbolts 3 disposed around the frame. FIGS. 1, 2, and 3 show frame 1 
comprising two frame parts 4 and 5, which are provided with recesses 6. 
Recesses 6 serve to receive cutters 7 and 8 which, as seen in FIGS. 2 and 
3, can be used in connection with spacer discs 9. Spacer discs 9 provide a 
certain cutter advancement, and consequently a certain response pressure, 
to be set. FIG. 3 shows an embodiment of the novel pressure relieving 
device wherein frame part 4 is provided with cutter 7 and frame part 5 
contains block 10. 
The novel pressure relieving device operates as follows: 
In the normal state, rupture disc 2 is in the position shown in FIGS. 1, 2, 
and 3. If, in the case of the embodiments of FIGS. 1 and 2, the pressure 
changes to a value which corresponds to the set response pressure, rupture 
disc 2 bulges in one direction or the other, presses against cutter 7 or 
8, and is cut out around its entire circumference by the cutter edge. In 
FIG. 3, an embodiment is represented wherein rupture disc 2 responds to a 
pressure change on one side, bulges in the direction of frame part 4 and, 
when the response pressure is reached, is cut out by cutter 7. 
While only a limited number of specific embodiments of the present 
invention have been expressly disclosed, it is, nonetheless, to be broadly 
construed and not to be limited except by the character of the claims 
appended hereto.