IE45220B1

IE45220B1 - Diaphragm safety valve

Info

Publication number: IE45220B1
Application number: IE1225/77A
Authority: IE
Inventors: F Cassali; M Montagnani; U Buzzi
Original assignee: Euratom
Priority date: 1976-06-18
Filing date: 1977-06-15
Publication date: 1982-07-14
Also published as: DE2727935A1; GB1580849A; FR2355226A1; LU77560A1; NL7706680A; IE45220L; FR2355226B1; IT1061768B; BE855792A

Abstract

The invention refers to the field of the valves of safety to membrane. [FR2355226A1]

Description

The object of the present invention is the provision of a diaphragm safety valve for pressurised media and having a predetermined failure point at which pressure is released. la the normally used diaphragm type safety valves, the valve opens because the diaphragm itself fails. Failure of the diaphragm due to a rise in pressure does not however always happen at the same level of pressure but ip .subject ta about 10 ta 20% uncertainty. The consequence of this is that there nay be a fairly wide divergence between the level of pressure which the diaphragm must safely withstand without failing and the level of pressure at which the diaphragm must reliably fail.

This means that the pressure reservoirs have to be over-aiaed, which is a'great eeo'nomio disadvantage. The lack of certainty of failure is due to the influence of a large number of difficultly controllable parameters on the strength of the diaphragm and any defects therein, the curvature of the diaphragm and any defects therein, the surrounding weld, faults in the material which may be very numerous in a large diaphragm, the system of railing, working, etc.

In the appended drawings, any corresponding elements bear the same reference, numeral.

Kg. 1 shows diagrams of two industrially produced types of valve.

In the first, type A, the element intended to fail is a diaphragm 1 with its concave side towards the pressurised ambient 2. The diaphragm made frora thin stainless steel sheet, is fixed by being welded along its periphery to an outer ring 3 which is in turn gripped between two flanges 4 provided uith seals 5· - 2^3330 la the second type, type B, shown at the bottom of rig. 1, the diaphragm 1 is disposed with its convex side towards the pressurised ambient 2. Thus, in an endeavour to determine the resistance of the diaphragm, another parameter (peak load collapse due to elastic failure), based on a more clearly defined characteristic such as the modulus of elasticity of the material, was introduced as a way of determining more satisfactorily the level of pressure at whieh the valve would fail. In reality, however, the degree of uncertainty still remains high '.a to the actual complexity of the element intended to fail and due at the same time to the influence of too many parameters on its resistance capacity. It should be said that in some valves of the more economical type, the diaphragm is not welded to the sealing ring, but that the seal is achieved by directly clamping the diaphragm, ths principles of resistance and failure as previously recalled remaining unaltered.

In order to obviate the aforesaid disadvantages, new concepts of diaphragm safety valves are proposed, the intention of these being to minimise to the gr&steob possible extent any uncertainty concerning 1die level of pressure at which the valve will fail.

According to the main characteristic feature of the invention, the valve comprises in the diaphragm structure whioh is affected by the pressure, a calibrated test bar arranged to support, tinder compression or tension, the diaphragm and resist rupture thereof, the test bar being calibrated to fail when a predetermined pressure is applied to - the diaphragm structure.

According to a further characteristic feature of the invention, the diaphragm comprises on its periphery two annular elastic plates 3 3 0 mechanically connected to a rigid ring fixed to the valve supporting structure and constituting the base of a cylinder coaxially aligned with the annular plates, the diaphragm being provided on the side opposite the pressurised ambient with a cylindrical support coaxial with the cylinder and connected mechanically to the said cylinder through a calibrated test piece fixed to a cross-member rigid with the cylinder itself.

The basic idea employed is that of introducing into the resistant structure an element, the resistance of which on the one hand is essential to the resistance of the structure itself but the failure of which on the other hand occurs at a clearly determined level of the pressure applied. The simplest and most practically usable resistant elements which have a clearly determined failure point are: - cylindrical test pieces which are stressed by traction and which are made from ductile material (steel) with a small rupture elongation limit (ia which case failure occurs by rupture) - slender test bars stressed by axial corcression (so that failure occurs by elastic instability due to a peak loading).

In the first case*, rupture occurs at levels of stress comprised within a margin of uncertainty of 1 to while in the second case the margin of uncertainty is reduced to In fact, in the first case, rupture depends not only on the stress applied but also on a few clearly defined parameters: - diameter of the test bar which may be defined with a high degree of accuracy and a minimum of error - composition and treatment of the material, factors which are also ·, easily definable -Λ45220 - micro deiecte in tho material; these are the only pammaters which cannot be clearly defined and they are in fact the main cause of the residual uncertainty, hut their incidence ia far less than in « the case of the diaphragm due to the lesser length of the resistant 5 element.

In the second case, then, failure depends practically only-on two types of clearly defined parameter; - geometrical characteristics of the element (length and diameter) - modulus of elasticity of the material, a very stable parameter whieh is insensitive to tne presence of micro defects.

This explains the precise detenainability of the level of stress at which failure of the resistant element occurs.

The diaphragm safety valves which are the object of the present invention are then conceived in such a way that one of the firstly described elements contributes in a clearly defined manner to the strength of the diaphragms when such an element fails, rupture of the diagrapha and openi.. of the valve follow immediately.

The invention will be better understood and the secondary characteristics and their advantages will become more readily manifest from the ensuing description of embodiments given by way of example.

It is understood that the description and the drawings are given solely by way of indication and imply no limitation.

The possible ways of constructing the safety valves proposed are illustrated in tiie longitudinal sectional views of Figs. 2 to 7.

Jig. 2 illustrates the valve with diaphragm supported by a traction - 5 4'ύ83° stressed sample located externally of the pressurised ambient.

Fig. 3 shows a more economical version of .Kg. 2 .

Kg, 4 shows the diaphragm supported by a traction stressed sample and located, inside the pressurised ambient.

. Kg. 5 shows a more economical verstion of that shown in the preceding figure.

Fig. 6 shows a valve with a diaphragm supported by an element subject to peak load and Kg. 7 shows a more economical version of this 'Kg. 2 shows the diaphragm 1 connected by heing welded to two peripheral annular sheets. 6 connected in turn to the rigid ring 3 whioh is clamped between the flanges 4 by means of bolts 14 and with interposed seals 5. The diaphragm 1 and the annular plates 6 constitute a diaphragm-bellows assembly which is deformable and which by itself is incapable of resisting even a very low pressure (so that it will certainly be ruptured by the calibrated pressure). The resistance of the diaphragm-bellows assembly to the operating pressure is then possible by virtue of the cylindrical support 7 acting on the diaphragm. The said support 7 is held by the test bar'8 and the cross-member 9 which is rigid with the cylinder 3' end thus with the flanges 4. It ie clear then that the force produced by the internal pressure acting - on the diaphragnis almost completely absorbed by the traction stressed test bar 8.

When this force exceeds the breaking load of the test bar, which has a clearly defined value (to between 1 and 2%) and which corresponds to the calibration value of the valve, the valve itself will obviox\sly - 6 open immediately. To prevent any lateral displacements or misalignments of tha cylindrical port 7, this latter is provided with aa outer circumferential shoulder 10.

Fig. 3 shows a more economical version of the previously described 5 valve. The diaphragm 1 is a simple flat sheet clamped in sealingtight fashion between the rigid ring 3 and the flanges 4 by means of the gasket 5 and the circular rib 15- The latter is supported and held slightly convex towards the pressurised ambient by the support 7 which, as in the cr ceding case, is connected to the ring 3 and thus to the flanges 4 by the test bar 8 and the rigid cross-member 9 iu the cylinder 3'. As ia the previous case, the test bar 8 is traction stressed by the pressure acting on the diaphragm and rupture of the test piece is immediately followed by failure of the diaphragm· Hg, 4 illustrates the val’.e with a diaphragm supported by a test bar which is traction stressed hut which is however located inside the pressurised ambient, This arrangement, simpler than the previous one, is advantageous, particularly if the pressurised gas is not yet subject to high tea culture or to fluctuations of temperature. In this case, tho diaphragm 1 and the annular plates 6 constituting an f assembly which is deformable and incapable of itself offering resistance, can be held directly in the centre of a welded core 11 by the test piece 8 which is traction stressed and also by the rigid ring 3 and thus by the flanges 4, Also in this case it is evident that upon failure of the test bar 8 by reason of traction, rupture of the diaphragm-bellows and therefore opening of the valve will follow immediately, A more economical version of the arrangement shown in Fig. 4 is I - 7 4 5 2 3 0 illustrated in Kg. 5· lu this case, the diaphragm is a simple sheet hold between the flanges 4 of the tube and subjected tc a slight tension by the test bar 8 through the central core 11. The mechanics of failure of the test piece and opening of the valve are similar to those previously described. fig. 6 shows the valve with the diaphragm supported by a peak load element. In the said drawing, reference numeral 1 denotes the diaphragm which is connected by welding to two annular sheets 6, connected in turn to the rigid ring 3, which is clamped between the flanges 4 through interposed gaskets 5· As in the ease shown in Fig. 2, the diaphrngnl end the annular plates 6 constitute a diaphragm-capsule assembly which is deformable and incapable of itself resisting even a very small pressure (so that it will reliably rupture under the calibrated pressure) The resistance of the diaphrags-bellows assembly to the operating pressure is then possible by reason of the presence of the cap 12 which is pressed against the diaphragm by the rod 8 which thus represents the element which is subjected to peak load and which is therefore subject to the phenomenon of elastic instability when the load acting on it exceeds the predetermined critical level. The rod 8 ie supported in that its upper end is rigidly connected to the cylinder 3* through a threaded bush 13 which permits of fine adjustment of the length of free inflexion of the rod and therefore the accurate calibration of the valve. Indeed, the force produced by the internal pressure acting on the diaphragm is almost completely absorbed by the rod 8 which is compression stressed at a peak loading. When the said loading exceeds the critical loading, so that the element 8 is subjected to ,the phenomenon of elastic instability, a loading which - -.· «ink* '.Γ, - 8 4522 has a clearly determined level (to within 0.5^), ana which corresponds to the calibrated rating of the valve, obviously the valve itself will open immediately. Fig. 7 shows a more economical version of Jig. 6 as previously described. Ihe diaphragm 1 is a simple flat sheet clamped in sealing-tight fashion between the rigid ring 3 and the flanges 4.

It is supported and held slightly convex towards the pressurised ambient by the cap 12 which ie subject to the thrust of the rod 8.

Also in this case, the greater part of the force produced by the internal pressure ?-. ,ing on the diaphragm will be discharged through the element 8, subjecting it to a peak loading. When the said force exceeds the value envisaged by calibration of the valve, the valve itself will open immediately.

Claims

1. A diaphragm safety valve for pressurized media, in whieh the diaphragm structure which is exposed to the pressure of the media comprises a,test bar arranged to support, under compression 5 or tension, the diaphragm and resist rupture thereof, the test bar being calibrated to fail, thereby allowing rupture of the diaphragm, when a predetermined pressure is applied to the diaphragm structure.

2. A valve according to Claim 1 in which the test bar is 10 mechanically connected by rigid supports to the structure which is subject to the pressure.

3. A valve according to Claim I or Claim 2 wherein the diaphragm has on its periphery two elastic annular plates the outer edge of one plate being connected to the periphery of the 15 diaphragm, the inner edge of the plate being connected to the inner edge of the other plate and the outer edge of the other plate being connected to a rigid ring fixed to the valve supporting structure and constituting the base of a cylinder coaxially aligned with the annular plates, the diaphragm having 20 on the side opposite the pressurized ambient, a cylindrical support coaxial with the cylinder and connected mechanically to the cylinder through the calibrated test bar fixed to a cross-member rigid with the cylinder itself.

4. A valve according to Claim 1 or Claim 2, wherein the 25 diaphragm, fixed mechanically at its periphery to the valve supporting structure by a rigid ring comprising the base of a cylinder, has on the side opposite the pressurized ambient and acting thereon, a cylindrical support coaxial with the cylinder and connected mechanically to the cylinder by the calibrated test - 10 4 523 0 bar fixed to a cross-member rigid with the cylinder itself,

5. A valve according to Claim 1 or Claim 2, wherein the diaphragm has on its periphery two elastic annular plates, the outer edge of cne plate being connected to the periphery of the 5 diaphragm, the inner edge of the plate being connected to the inner edge of the other plate and the outer edge of the plate being connected to a rigid ring constituting the base of a support cylinder and fi-.:-0 to tho structure supporting the valve, the diaphragm having on the pressurized side, the calibrated test 10 bar mechanically connected to it and supproted by a cross-member rigid with the support cylinder.

6. A valve according to Claim 1 or Claim 2 wherein the diaphragm is mechanically fixed at its periphery to the structure supporting the valve by a rigiu ring constituting the base of a 15 support cylinder, the diaphragm having on the pressurized side, and acting thereon, the calibrated test bar mechanically fixed to it and supported by a ross-member rigid with the cylinder.

7. A valve /cording to Claim 1 or Claim 2 wherein the diaphragm has on its periphery two elastic annular plates, 20 the outer edge of one plate being connected to the periphery of the diaphragm, the inner edge of the plate being connected to the inner edge of the other plate and the outer edge of the other plate being connected to a rigid ring fixed to the supporting structure of the valve and constituting the base of a support 25 cylinder, the diaphragm having on the side opposite the pressurized ambient, a cap which is acted upon by the calibrated test bar fixed by a threaded bush to a cross-member rigid with the support cylinder.

8. A valve according to Claim 1 or Claim 2 wherein Mie diaphragm Is mechanically fixed at its periphery to the supporting structure of the valve, hy a ring constituting the hase of a support cylinder, tlie diaphragm having, on the side . 5 opposite the pressurized ambient, a cap which is acted upon hy the calibrated test bar fixed by a threaded hush to a cross-member rigid with the support Oylinder.

9. O A valve according to any one of the preceding Claims, wherein the valve, supporting structure comprises two flanges

10. Fixed hy holts with interposed sealing-tight gaskets. 10, A valve according to Claim 9, wherein the valve supporting structure comprises two flanges fixed hy bolts with an interposed sealing-tight gasket and a circular rib. il. A diaphragm safety valve for pressurized media

11. 15 constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figures 2 to 7 of the accompanying drawings.