GB2316450A

GB2316450A - Pressure relief device

Info

Publication number: GB2316450A
Application number: GB9717896A
Authority: GB
Inventors: Mark Hayles
Original assignee: Elfab Ltd
Current assignee: Elfab Ltd
Priority date: 1996-08-23
Filing date: 1997-08-22
Publication date: 1998-02-25
Anticipated expiration: 2017-08-22
Also published as: GB2316450B; GB9717896D0; GB9617679D0

Abstract

A pressure relief device comprises a domed reverse bursting disc (2), a support member (8) having an annular flange portion (10) and flexible arm portions (14) extending from circumferentially spaced regions of said flange portion (10) to support the concave surface of the dome portion (6) of the disc (2), and a knife blade member (18) having an annular flange portion (20) and substantially rigid knife blade portions (24) extending from circumferentially spaced regions thereof to underlie the dome portion (6) of the disc (2), each knife blade portion (24) including a cutting edge (26) disposed substantially on a common line of latitude of the dome portion (6) of the disc (2), whereby initial reversal of the dome portion (6) of the disc (2) causes the arm portions (14) of the support member (8) to snap through the knife blade member (18) to positions axially inwardly of said line of latitude, the unsupported dome portion (6) of the disc (2) reversing into forcible engagement with, to be ruptured by, said cutting edges (26) of the knife blade portions (24).

Description

PRESSURE RELIEF DEVICE This invention relates to safety pressure relief devices, and more particularly to reverse bursting disc assemblies incorporating knife blades or the like for rupturing the reversing disc.

It is established practice to provide reverse bursting disc assemblies for detecting, for example, very small pressure differentials, as low as 1 inch water gauge, the assemblies incorporating knife blades arranged, on reversal of the disc, to puncture the disc and relieve the associated system.

However, the known assemblies suffer from a number of disadvantages. The knife blades are invariably welded into, to be integral with, the outlet holder ring of the assembly, which is therefore a substantial, relatively expensive component. If the knife blades corrode or become blunt and require replacement, this can be a costly matter.

In very low pressure situations, the disc tends to roll through from its normal condition to its reversed condition, and there is very little energy associated with reversal. Although the knife blades are arranged to provide an initial pin-hole burst centrally of the disc, subsequent tearing of the disc to give sufficient relief cannot always be ensured.

It would be desirable to be able to provide a pressure relief device incorporating means for bursting the disc on reversal which are more efficient in operation, particularly in low pressure situations, and more economical to manufacture than heretofore.

According to the present invention there is provided a pressure relief device comprising a reverse bursting disc having an annular flange portion and a central concave/convex dome portion, a support member for the disc having an annular flange portion and a plurality of flexible arm portions extending from circumferentially spaced regions of said flange portion of the support member to underlie and support the concave surface of the dome portion of the disc, and a knife blade member having an annular flange portion and a plurality of substantially rigid knife blade portions extending from circumferentially spaced regions of said flange portion of the knife blade member to underlie the concave surface of the dome portion of the disc between the arm portions of the support member, each knife blade portion including a cutting edge disposed substantially on, to extend along an extent of, a common line of latitude of the dome portion of the disc, the arrangement being such that, when a predetermined pressure differential exists across the dome portion of the disc equal to the bursting pressure of the disc, initial reversal of the dome portion causes the arm portions of the support member to snap through the knife blade member to positions axially inwardly of said line of latitude, the unsupported dome portion of the disc reversing into forcible engagement with, to be ruptured by, said cutting edges of the knife blade portions.

Thus it will be appreciated that use of the energy from the fluid acting upon the disc is optimised in that, on snap through of the arm portions, all the energy in the fluid is available to cause reversal of the now unsupported dome portion of the disc which therefore impacts violently onto the cutting edges of the knife blade portions to form tears in a plurality of circumferentially spaced positions in the dome portion around said line of latitude, thereby relieving the undesirable pressure conditions in the associated system.

Conveniently the arm portions of the support member, of which there are preferably three, are symmetrically disposed about the support member and each extends from the flange portion to a common junction piece which, on assembly of the device, underlies the central regions of the dome portion of the disc.

In one embodiment of the invention, particularly suited to low pressure situations, the support member and the knife blade member comprise separate components, with the arm portions of the support member being of thinner gauge material than that of the knife blade member.

In an alternative embodiment of the invention, particularly suited to higher pressure situations where more energy is available from the fluid under control, the support member and the knife blade member may be integrated into a single component comprising an annular flange portion from which extend, alternately and symmetrically about said flange portion, a plurality of flexible arm portions and a plurality of knife blade portions.

The reverse bursting disc may be of a thin, flexible material such as plastic, for example Teflon PFA, or metal, while the support member and the knife blade member are preferably of metal, for example stainless steel.

The device may further include, to the convex side of the dome portion of the disc, a cover member comprising an annular flange portion and an apertured, concave/convex dome portion.

In the event that the device is designed to give two-way relief protection, said cover member may comprise a forward bursting disc the dome portion of which, as well as being apertured, is provided with a plurality of scores or slots therein to determine the forward burst pressure thereof.

If one way relief protection only is required, the cover member can comprise a non-opening vacuum support member the whole of the dome portion of which is provided with a symmetrical array of apertures therein.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which: Fig. 1 is an exploded perspective view of a device according to the invention; Fig. 2 is a plan view from above of the support member of the device of Fig. 1, and Fig. 3 is a plan view from above of the knife blade member of the device of Fig. 1.

Referring to the drawings, there is shown a double-acting pressure relief device according to the invention adapted for connection to a storage vessel or the like to protect the vessel against vacuums such as could be created on emptying fluid from the vessel and against overpressure of fluid within the vessel.

The invention is particularly suited to relieve very low pressure vacuums, for example as low as one inch water gauge.

The illustrated device is arranged to be clamped between inlet and outlet support rings (not shown), and comprises a reverse bursting disc indicated generally at 2 of a thin, flexible plastics material such as Teflon PFA, the disc including an annular flange portion 4 and a concave/convex dome portion 6.

The disc 2 seats on, to be supported by, a snap ring indicated generally at 8 and including an annular flange portion 10, a transitional region 12 conforming with the equivalent region of the dome portion 6 of the disc 2, and three curved arm portions 14 extending symmetrically from circumferentially spaced parts of the transitional region 12 to terminate in a common central junction piece 16.

The curvature of the arm portions 14 conforms substantially with that of the dome portion 6 of the disc 2, and the circular junction piece 16 underlies the central regions of the dome portion 6 of the disc 2.

The snap ring 8 is of a thin flexible material, for example stainless steel, the construction of which is such that, on the application of a downward force, (as viewed in Fig. 1) on the junction piece 16, the downward movement of the junction piece 16 results in the arms 14 becoming stressed under the compressive load applied thereto.

Once a predetermined position of the junction piece 16 is reached, this position being a function of the dome height of the snap ring 8/disc 2, the gauge and type of the material of the arm portions 14, and the overall dimensions of the snap ring 8, the build-up of compressive energy in the arm portions 14 is released by said arm portions 14 snapping through on themselves to positions in which the junction piece 16 is located to the other side of the flange portion 10.

The device further comprises a knife blade ring indicated generally at 18 and including an annular flange portion 20, a transitional region 22 conforming with the equivalent regions of the disc 2 and the snap ring 8, and three equi-spaced knife blade portions 24 forming upward and inward extensions of the transitional region 22 disposed symmetrically about said region 22.

More particularly, each knife blade portion 24 is of curved section corresponding with the curvature of the dome 6 and the arm portions 14, and terminates in a serrated knife blade edge 26, the three edges 26 being located in a common plane parallel with that of the flange portion 20 with the serrations located in the envelope of the dome containing the knife blade portions 24.

The knife blade member 18 is of relatively heavy gauge metal, preferably stainless steel.

The illustrated device, which is designed to provide for two-way pressure relief, is completed by a forward bursting disc indicated generally at 28 and including an annular flange portion 30 and a central concave/convex dome portion 32. The dome portion 32 is formed with an array of apertures 34 symmetrically disposed thereabout, and four equi-spaced longitudinal slots 36 constituting lines of weakness in the dome portion arranged to provide for forward bursting of the disc at a predetermined burst pressure in conventional manner.

The described device operates as follows.

In the presence of a vacuum to the concave side of the dome portion 6 of the disc 2, fluid, for example atmospheric air, to the convex side of said dome portion 6 pressurises the convex side of the dome portion 6 by way of the holes 34 in the disc 28, which, in this condition of the associated system, acts as a cover to the overall assembly.

This pressure is applied to the arm portions 14 of the snap ring 8, which, as detailed above, snap through the flange portion 10 with the dome portion 6 of the disc 2 closely following.

The dome portion 6 of the disc 2 then impacts violently on the relatively heavy gauge knife blade portions 24 of the knife blade member 18 the edges 26 of which instantaneously form holes in three symmetrical positions about the dome portion 6 of the disc 2. The vacuum is thus relieved.

If there is a sufficiently high volume to relieve within the associated vessel, the energy available on reversal may be sufficient to lead to full bore opening of the disc 2. In extreme cases, part of the dome portion 6 may become separated from the remainder, the junction piece 16 of the snap ring serving to hang onto this separated part and prevent it from entering the system to cause potential damage.

When used to protect a vessel or the like against overpressure, the device of the invention functions in relatively conventional manner. In this situation, the dome 2 serves to provide an airtight seal and, on the application of pressure to the concave side thereof, the dome portion 2 transfers this pressure in the form of a tensile load onto the pre-weakened dome portion 32 of the disc 28. When the pressure on the dome portion 32 reaches the predetermined burst pressure, the dome portion 32 fails and pressure is relieved.

In the event that the device is not required to provide two way relief protection, but only to provide for low pressure relief in one direction, the disc 28 can be dispensed with and replaced by a non-opening vacuum support comprising an annular flange portion and concave/convex dome portion the whole of which is provided with a symmetrical array of apertures therein, thus allowing for more pronounced opening of the disc 2 under low volume/energy conditions because of the greater percentage free flow area therethrough.

Clearly the precise construction and materials of the components of the device can vary from those described and illustrated depending upon the particular application of the device.

For example, particularly in higher pressure situations, the snap ring and the knife blade member may be integral with one another with knife blade portions and arm portions extending alternately and symmetrically from a common flange portion, while the number of arm portions and knife blade portions may be other than three.

It will be appreciated that the material of the disc 2 is chosen to suit burst pressures in the low magnitude direction, and may be metal or plastic, the material and construction of the snap ring 8 is chosen to tune the low pressure snap mechanism and control the failure of the disc 2 towards burst in the low magnitude direction, and the heavier gauge metal knife blade 18 is designed to create multi-hole failures of the disc 2 which, on relief, will spread to connect with each other and hence lead to full bore relief conditions across the low pressure relief system.

It will be appreciated that the knife blade member of the device of the invention is of relatively simple construction and is relatively economical to manufacture. Replacement is a simple matter not involving other components of the device and is relatively inexpensive. The multitude of knife blade portions is such as to ensure effective relief of the associated vessel even in extremely low pressure situations.

Claims

1. A pressure relief device comprising a reverse bursting disc having an annular flange portion and a central concave/convex dome portion, a support member for the disc having an annular flange portion and a plurality of flexible arm portions extending from circumferentially spaced regions of said flange portion of the support member to underlie and support the concave surface of the dome portion of the disc, and a knife blade member having an annular flange portion and a plurality of substantially rigid knife blade portions extending from circumferentially spaced regions of said flange portion of the knife blade member to underlie the concave surface of the dome portion of the disc between the arm portions of the support member, each knife blade portion including a cutting edge disposed substantially on, to extend along an extent of, a common line of latitude of the dome portion of the disc, the arrangement being such that, when a predetermined pressure differential exists across the dome portion of the disc equal to the bursting pressure of the disc, initial reversal of the dome portion causes the arm portions of the support member to snap through the knife blade member to positions axially inwardly of said line of latitude, the unsupported dome portion of the disc reversing into forcible engagement with, to be ruptured by, said cutting edges of the knife blade portions.

2. A pressure relief device as claimed in claim 1 in which the arm portions of the support member are symmetrically disposed about the support member and each extends from the flange portion to a common junction piece which, on assembly of the device, underlies the central regions of the dome portion of the disc.

3. A pressure relief device as claimed in claim 2 in which there are three arm portions of the support member.

4. A pressure relief device as claimed in any one of claims 1 to 3 in which the support member and the knife blade member comprise separate components, with the arm portions of the support member being of thinner gauge material than that of the knife blade member.

5. A pressure relief device as claimed in any one of claims 1 to 3 in which the support member and the knife blade member are integrated into a single component comprising an annular flange portion from which extend, alternately and symmetrically about said flange portion, a plurality of flexible arm portions and a plurality of knife blade portions.

6. A pressure relief device as claimed in any one of claims 1 to 5 in which the bursting disc is of a thin flexible material, and the support member and knife blade member are of metal.

7. A pressure relief device as claimed in any one of claims 1 to 6 and further including, to the convex side of the dome portion of the disc, a cover member comprising an annular flange portion and an apertured, concave/convex dome portion.

8. A pressure relief device as claimed in claim 7 in which the cover member comprises a forward bursting disc the dome portion of which, as well as being apertured, is provided with a plurality of scores or slots therein to determine the forward burst pressure thereof.

9. A pressure relief device as claimed in claim 7 in which the cover member comprises a non-opening vacuum support member the whole of the dome portion of which is provided with a symmetrical array of apertures therein.

10. A pressure relief device substantially as described with reference to and as illustrated by the accompanying drawings.