GB2111593A - Pressure relief apparatus - Google Patents

Abstract

A pressure relief panel comprising a-pair of frames (16) surrounding a bursting sheet (26), the sheet being provided with slots (32-35) to control the burst pressure of the sheet and to enable the sheet to petal on bursting. The slots extend from the corners of the frames to a central region, there being provided on one side of the sheet of a pressure damping apparatus in the form of a central support carried by legs (17-20) extending from the corners of the frame towards a central boss (25), the support being screwed through the boss and into contact with the central region of the panel. A vacuum support in the form of a metal mesh may be located on the other side of the sheet. <IMAGE>

Description

SPECIFICATION Pressure relief apparatus This invention relates to pressure relief panels and has particular but not exclusive reference to pressure relief panels operating under cyclic pressure conditions.

It is known to provide pressure relief panels essentially comprising a metal sheet supported by and located between a pair of frames of the general shape of picture frames. The sheet is normally rectangular, but other shapes such as circular or trapezoidal can be manufactured as required. The sheet is clamped between the frames and is normally grooved or otherwise provided with zones of weakness. The grooves are frequently in the form of slots extending from the corner regions of each corner of a four sided frame towards the central region. Under pressure the panel relieves by blowing outwardly and the four triangular portions petal outwardly to open up a space through which fluid can escape to relieve pressure.Such pressure relief panels are frequently of a significant size, typically 120cm x 1 OOcm. Clearly, the larger the panel the more the panels will flex during cyclic pressure conditions.

They are designed to operate at relatively low burst pressures, down to 0.07 bar.

The term "outwardly" as used herein as intended to indicate the side of the panel which is normally at a lower pressure compared to the pressure acting to burst the panel. Thus in the case where there are no pressure cycles the outward side of the panel is always at a lower pressure than the inner side. On bursting the panel moves towards the outward side under the influence of pressure from the inner side.

By the present invention there is provided a pressure relief panel comprising a sheet located between a pair of frames disposed around the periphery of the sheet, the sheet having one or more zones of weakness formed therein, the panel being adapted and arranged to relieve pressure by the sheet blowing outwardly under the influence of a pressure above a predetermined level, there being provided a support for the sheet on the outer side thereof.

The support is preferably provided in the central region thereof. The sheet may be a composite sheet. Each sheet may comprise at least two layers, one at least of the layers being of metal.

Preferably the sheet is formed of three layers. The zones of weakness are preferably in the form of slots or grooves in the outer layer of the sheet. The support may be bridged from one of the frames by legs substantially coincident with but spaced from one or more of the slots or grooves. rhere may be provided a vacuum support on the inner side of the panel. The panel may be rectangular with four grooves in the outer layer of the sheet, one extending from the region of each corner towards a central region. Each groove may terminate in a hole. The four holes may be arranged at unequal distances one from the other. The layer on the outer side may be provided with slots throughout its entire thickness. The inner layer may be a plastics material or thin metal membrane supported by and spacing the outer layers. The support may be provided with pressure damping means.The support may be a bolt screw threaded through a boss supported by the legs. The pressure damping means may comprise a resilient facing member located on the end of the bolt adjacent the sheet.

The vacuum support may be in the form of rods or a wire mesh located adjacent the inner surface of the sheet. The vacuum support may be sandwiched together with the sheet between the pair of frames.

The support may extend over an area of less than the area between the four holes of an equal area to that between the four holes or may extend over a greater area than that of the four holes. In a preferred form the area of the support is less than or equal to the area between the four holes.

By way of example embodiments of the present invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a perspective view of a pressure relief panel; Figure 2 is a perspective view of a sheet and adjacent vacuum support; Figure 3 is a perspective view of a panel on one face and being provided with a support; Figure 4 is an enlarged view of the boss and support of Figure 3; Figure 5 is a part sectional view of a support and central region of the panel; and Figure 6 is a perspective view of discs attached to the panel to tie the segments together.

Referring to Figure 1 this shows a perspective view of a conventional form of burst panel. The panel is made up of a three layer sheet 1 clamped between a pair of picture frame members 2 and 3.

The panel is provided with a set of slots 4, 5, 6, and 7. Each slot such as slot 4 extends from a hole in the region of one of the corners such as corner 8 of the panel towards a central region where it terminates in a hole 9. It can be seen that there are four central holes and one of the holes, hole 1 0, is so positioned that the distance between each of the holes is unequal.

In use the panel is used as a safety provision in such pieces of equipment as conveyors or electrostatic precipitators where there is a danger of transient high pressures from small explosions etc which might otherwise cause damage to the entire assembly. The panel is so designed that when the pressure on the inner side of the panel exceeds a given level the sheet is burst outwardly selectively failing along the zones of weakness 4, 5, 6 and 7. Because the space between the holes 9, 10 is unequal the central region 11 of the panel stays attached to one of the triangular petals which are formed when the panel relieves.

In certain circumstances the panel can be subjected to vacuum conditions caused by the pressure on the inner side of the panel falling below that on the outer side. Because the panel is frequently designed to resist pressure in one direction only it is conventional practice to provide a vacuum support for the panel in such a circumstance.

Figure 2 illustrates schematically such a support. The support essentially comprises a wire mesh 12 which is formed from a series of wire strands welded to one another where they cross such as at points 13. The ends of the wires such as ends 14 are firmly held between the picture frame members 2, 3 and one side of the sheet 1.

It has now been found that unexpectedly failures are occurring in certain circumstances, even where vacuum supports are provided, although the over pressure within the chambers protected by the pressure relief panels do not exceed those which the panel is designed to withstand. It has now been found that these failures can be reduced considerably by the provision of a support on the outer or pressure side of the relief panel as is shown, for example, clearly in Figure 3.

By way of explanation it is believed that the failures are caused by pressure cycling and the pressures, although not exceeding those which the panel is designed to withstand, can cause some form of harmonic vibration in the panel which can give rise to premature failure.

Referring to Figure 3 this shows, on the outer side, a framework indicated generally by 1 5 which is attached to one of the frames 1 6. The framework is in the form of legs 17, 18, 19, 20 which are supported by feet 21, 22, 23, 24. The feet are permanently attached to the frame 1 6. By means of the legs 1 7 to 20 a central boss 25 can be provided over the central region of the sheet 26. A bolt 27 (Figure 4) is screwed through the central boss and in contact with the central region of the sheet 26. The bolt 27 is provided with a hexagonal recess 28 so that it can be screwed into contact with sheet 26. At the lower end of the bolt 27 there is provided a bearing 29 to the lower end of which is attached a plate 30 and a thin sheet of rubber 31. The rubber 31 acts as a damper to restrict vibration of sheet.It is believed that the mechanism damps vibration in the sheet thus permitting normal operation of the panel even where there are cyclic pressure conditions within the container to which the panel is associated. It will be seen that the legs 17 to 20 are located over and spaced slightly from the grooves 32, 33, 34, and 35. By this means the sheet is able to petal outwardly and the triangular portions between the grooves 32 to 35'open up without contacting the legs 17 to 20. Thus the support does not interfere with the bursting of the panel but it does resist the cyclic pressure vibrations and thus enable the panel to operate in a static mode at pressures nearer its ultimate bursting pressure.

There may be provided a lock nut to secure bolt 27 to the boss.

It will be appreciated that if the feet 21 to 24 were of sufficient length the legs 1 7 to 20 need not coincide with the slots 32 to 35 but the embodiment illustrated in Figure 3 is a particularly advantageous embodiment.

As can be seen in Figure 5 the sheet comprises a composite sheet having an outer layer 36 and an inner layer 37 spaced by a plastics membrane layer 38. The grooves 32 to 35 and the holes would thus extend completely through the sheet 36 but not through sheet 37 and the central region would correspond to the uncut portion 39 of the sheet.

In order that the segments of the sheet may be more firmly held together to resist flexing there may be provided discs spot welded on one side or the other of the groove or slit in the sheet. Thus as illustrated in Figure 6 a pair of discs 41,42 are secured to the panel indicated generally by 43.

The disc 41 is spot welded at 44 to one side of the slit 45, the other side being unrestrained. Similarly disc 42 is spot welded at 46 whereas the side 47 is unrestrained. These discs tie the segments together but permit them to separate on bursting.

Obviously a single strip could be used in place of the multiple discs.

Claims (18)

1. A pressure relief panel comprising a sheet located between a pair of frames disposed around the periphery of the sheet, the sheet having one or more zones of weakness formed therein, the panel being adapted and arranged to relieve pressure by the sheet blowing outwardly under the influence of a pressure above a predetermined level, there being provided a support for the sheet on the outer side thereof.

2. A panel as claimed in Claim 1 in which the support is provided in the central region.

3. A panel as claimed in Claim 1 or Claim 2 in which the zones of weakness are in the form of slots or grooves in the sheet.

4. A panel as claimed in Claim 3 in which the support is bridged from one of the frames by legs substantially coincident with, but spaced from, one or more of the slots or grooves.

5. A panel as claimed in any one of Claims 1 to 4 in which there is provided a vacuum support on the inner side of the panel.

6. A panel as claimed in any one of Claims 1 to 5 in which the sheet is a composite sheet.

7. A panel as claimed in Claim 6 in which the sheet includes at least two layers, one at least of the layers being of metal.

8. A panel as claimed in Claim 7 in which the sheet is formed of three layers, the layer on the outer side being provided with slots throughout its entire thickness.

9. A panel as claimed in Claim 8 in which the inner layer is of plastics material or is a thin metal membrane supported by and spacing the outer layers.

10. A panel as claimed in any one of Claims 7, 8 or 9 in which the panel is rectangular with four grooves, one extending from the region of each corner towards a central region.

11. A panel as claimed in Claim 10 in which the grooves are formed in the outer layer and terminate in a hole.

12. A panel as claimed in Claim 11 in which the four holes are arranged at unequal distances one from the other.

13. A panel as claimed in any one of Claims 1 to 1 2 in which the support is provided with pressure damping means.

14. A panel as claimed in Claim 4 in which the support is a bolt screw threaded through a boss supported by the legs.

15. A panel as claimed in Claim 14 in which there is provided pressure damping means comprising a resilient facing member located on the end of the bolt adjacent the sheet.

16. A panel as claimed in any one of Claims 1 to 1 5 in which there is provided a vacuum support in the form of rods or a wire mesh located adjacent the inner surface of the sheet.

17. A panel as claimed in Claim 1 6 in which the vacuum support is sandwiched together with the sheet between the pair of frames.

18. A panel as claimed in Claim 13 when appended to Claim 11 or Claim 12 in which the support extends over an area less than or equal to the area between the four holes.

1 9. A pressure relief panel substantially as herein described with reference to and as illustrated by Figures 1 to 5 of the accompanying drawings.