GB2048524A

GB2048524A - Rupture-sheet safety valve

Info

Publication number: GB2048524A
Application number: GB8010176A
Authority: GB
Original assignee: Phoenix Armaturen Werke Bregel GmbH
Current assignee: Phoenix Armaturen Werke Bregel GmbH
Priority date: 1979-04-04
Filing date: 1980-03-26
Publication date: 1980-12-10
Also published as: DE2913463B1; DE2913463C2; JPS55135276A; NL8001143A; ES489351A1; FR2453343A1; IT8021217A0; IT1141514B; BE882588A

Abstract

The valve is used for safeguarding a vessel by limiting the maximum pressure therein and comprises a housing (1) with a removable cover (2). Within the housing there is a spring- biased valve closing member (6) and a rupture-sheet assembly (4) disposed in the discharge direction downstream of the valve closing member. A duct (16) interconnects the interior of the vessel to be safeguarded with a space (22) between the valve closing member and the rupture-sheet and an auxiliary valve (17) is located in the duct and is mechanically operable by the rupture-sheet to maintain the auxiliary valve in an open position while the rupture-sheet is intact. <IMAGE>

Description

SPECIFICATION A rupture-sheet safety valve.

The present invention relates to a rupture-sheet safety valve.

A rupture-sheet safety valve is known of the type comprising a combination of a spring-loaded safety valve, which opens a pipe line or such like counter to the action of its spring when there is a specific excess pressure in a vessel to be protected, and a rupture-sheet arrangement involving a rupturesheet of specific size and strength which breaks or is sheared off when a specific excess pressure is reached in the protected vessel.A safety vessel of this type avoids the disadvantages associated with the two elements individually: a spring-loaded safety valve has the advantage of remaining open only until a dangerous excess pressure in the vessel has been reduced and of then closing so that the entire contents of the vessel are not discharged and it also has the advantage of being able to respond as frequently as required without destroying any components thereof, but it does therefore have the disadvantage that even before the blowing-off pressure is reached, as a result of the decreasing force of the closing element on its valve seat, this force becoming less as the vessel pressure increased, this valve seat starts to become untight.

Rupture-sheet arrangements, however, have the advantage of being absolutely sealed until they respond, i.e. the rupture-sheet is sheared off, but the rupture-sheet is then destroyed and has to be replaced, making reclosure impossible so that the vessel empties completely.

A rupture-sheet safety valve is known from the design 4 JQ of the Chlorine Institute Inc., maintenance instructions for this being provided in the 2nd Edition of 1st Nov. 1967. In this known construction, the rupture-sheet arrangement is arranged in the discharge direction upstream of the safety valve, i.e.

the rupture-sheet lies next to the vessel interior and the safety valve is screwed on externally. The chamber between the rupture-sheet and the safety valve is therefore closed in the normal state so that there is a pressure in this chamber which cannot be exactly determined and which can fluctuate between the ambient pressure and the pressure at which the safety valve responds. This pressure, which is dependent on contingencies and subject to fluctuations, in the space between the safety valve and the rupture-sheet acts on these counter to the action of the internal pressure of the vessel, so that the response of the rupture-sheet arrangement and thus of the rupture-sheet safety valve always takes place under changing and inaccurately defined pressures.

A further disadvantage of the known valve cont sists in that at the time of the operation and blow-out, fragments of the rupture-sheet may be caught in the safety valve, particularly between its closing member and seat and may prevent its reclosure after the excess pressure has been dispersed. As a consequence, permanent leakage may result causing the vessel to empty slowly.

It is also a disadvantage that when the rupture sheet is replaced, as is required after the rupture sheet safety valve has operated or also as may be required for maintenance reasons, it is necessary firstly for the safety valve to be removed which means that prior to this operation the vessel has to be depressurized.

Similar disadvantages apply for a further rupture sheet safety valve which is known as the applicants' design PAW 3384. With this design, the rupturesheet is clamped directly over, i.e. in the discharge direction downstream of the valve closing element, so that when this opens it causes the sheet to shear off. The force of the spring holding the valve closing element in the closed position acts from outside through the rupture-sheet.

It is also to be considered a disadvantage with this construction that there is rather a great difference between the response pressure at which the opening of the rupture-sheet safety valve beings and its closure after the excessive over-pressure has been dispersed, which is explained by the fact that for operation the shear strength of the rupture-sheet has to be overcome at the same time as the force of the closing spring of the safety valve, while for closing only this last force of the closing spring is then available. As a result of regulations, at least in Germany, the difference between the response pressure and the closing pressure may not be greater than 10% and this cannot always be achieved with the known rupture-sheet safety valve under consideration.

According to the present invention there is provided a rupture-sheet safety valve comprising: a valve closing member subjected, in use, to the pressure within a vessel to be safeguarded; a spring biasing the closing member towards its closed position; a rupture-sheet disposed in the discharge direction downstream of the valve closing member, which rupture sheet is clamped about its edge; a duct issuing from a point which, in use, is in communication with the interior of the vessel and opening into a space between the valve closing member and the rupture-sheet; and an auxiliary valve located in the duct and mechanically operable by the rupture-sheet to maintain the auxiliary valve in an open position while the rupturesheet is intact.

Thus, the space between the valve closing mem- ber and the rupture-sheet which is positioned further downstream is normally under the internal pressure of the vessel so that only the shear strength of the rupture sheet must be opposed for the response and thus the response is achieved at an exactly fixed pressure prescribed by the parameters of the rupture sheet arrangement. The closure is effected at a final pressure which is exactly prescribable by the parameters of the safety valve.

When the rupture-sheet is sheared, no fragments of the rupture-sheet reach the safety valve to impair its operation. The rupture-sheet is easily changed, it being merely necessary to ensure that, during the operation, the vessel pressure cannot exceed the response pressure of the safety valve.

Moreover, the safety valve according to the inven tion produce the further advanta9e that, as result of the buffer effect of the space which is in connection with the vessel interior via the auxiliary valve, held in the open position and thus acting as a throttle point, short pressure surges still cannot lead to the response because the pressure in the space only equalises with the internal pressure of the vessel after a certain delay.

For a better understanding of-the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows a cross-section through one embodiment of a rupture-sheet safety valve according to the present invention; Figure 2 shows a partial cross-section through a second embodiment of a rupture-sheet safety valve according to the present invention; Figure 3 shows a partial cross-section through a third embodiment of a rupture-sheet safety valve according to the present invention; Figure 4 shows a section through a rupture-sheet arrangement with an adjustable push rod position; Figure 5 shows a section according to Figure 4 with a bellows seal of the push rod; Figure 6 shows the arrangement of a blocking valve in an auxiliary valve duct;; Figure 7shows a cross-section through an embodiment similar to that shown in Figure 1, butwith another method of keeping the rupture-sheet arrangement open after its bursting; and Figure 8 shows a further spring-loaded rupturesheet arrangement.

A rupture-sheet safety valve shown in Figure 1 comprises a housing 1 closed by a cover 2, in which a safety valve 3 and a rupture-sheet arrangement 4 are housed.

Appertaining to the safety valve is a valve seat 5 onto which a valve closing member 6 is pressed by a closing spring 7. The other end of the closing spring 7 bears against a cross-member 8 fixed to the housing and on which a guide sleeve 9 for the valve closing member 6 is also attached.

The housing has a flange 10 by means of which it may be attached to a vessel or such like which has to be protected against excess pressure. The duct issuing from this flange 10 on the vessel side is blocked at first by the safety valve 3 described above.

Placed in the flow direction downstream of the safety valve is the rupture-sheet arrangement 4 having a rupture-sheet 11 which is clamped at its outer edge between rings 12. In the case of the present embodiment, the rupture sheet is not formed as a circular disc, but is annular and its inner edge is clamped between plates 13. The two plates 13 are mutually braced by means of a thread connection 14, the screw having an elongation in the form of a push rod 15 which projects towards the safety valve 3.

In the valve closing member 6 of the safety valve there is a duct 16 which extends in the axial direction and in which an auxiliary valve 17 is housed. The auxiliary valve 17 consists of a mushroom-shaped closing element 18 and a spring 19 urging the element 10 ;n the direction to close the valve 17. In the normal operating position, the closing element 18 is lifted a small way from its seat, counter to the effect of its spring 19, by the push rod 15.

A circumferential projection 20 is formed on the upper plate 13 and is positioned to co-operate with arresting arms 21, which are fixed to the housing, in such a way that when the rupture-sheet arrangement 4 moves upwards in order to open, the arresting arms 21 engage behind the projection 20 and hold the rupture sheet arrangement in the open position.

During operation, the rupture-sheet safety valve described above operates as follows: In the normal state, when the pressure in the interior of the protected vessel has not reached the response pressure at which the blow-off should begin, the components are in the position shown in Figure 1. The pressure within the vessel also exists in a space 22 between the safety valve 3 and the rupture sheet arrangement 4 via the auxiliary valve 17 which is held open by the push rod 15. The rupture sheet 11 withstands this pressure, but is subjected to shearing forces on the circular line between the rings 12 and the plates 13.

When the pressure within the vessel rises above the value which can be withstood by the rupture sheet, this sheet is sheared off along the aforementioned circular line and the rupture sheet arrangement 4 springs upwards, so that the arresting arms 21 engage behind the circumferential projection 20 and restrain the arrangement. In this way the closing element 18 of the auxiliary valve 17 is released and moves into the closing position due to the spring 19 and the internal pressure of the vessel.

At the same time, the pressure in the space 22 suddenly falls to a counter pressure which is the ambient pressure or the pressure in the blow-off line, so that the difference between the internal pressure of the vessel and the counter pressure is across to the safety valve 3 enabling the valve 3 to fulfil its normal function. When the valve 3 is dimensioned and adjusted so that it opens at a pressure which is somwhat below the response pressure of the rupture-sheet arrangement 4 or which has just reached this pressure, then the valve closing member 6 is raised directly after the rupturesheet arrangement has operated and remains open until the internal pressure of the vessel falls to the blow-off pressure.

After a permissible pressure has been reestablished in the vessel and it is certain that the pressure cannot rise again, the sheared off rupturesheet 11 is simply replaced by a new one after the cover 2 has been removed.

Figure 2 shows an embodiment in which an angled duct 27 is constructed in a valve closing member 26, so that the auxiliary valve 17 is housed in a section of the duct 27 extending at right angles to the axial direction of the closing member 26. The closing element 18 is held open in the normal state by a rupture sheet arrangement 4 placed at the side in a blow-off connecting piece 28 and with a push rod 15 pressing on a pin-shaped projection of the closing element 18.

The valve closing member 26 is urged onto its valve seat 5 by a pressure rod 30 via a ball 31.

Figure 3 shows the most essential components and their mutual arrangement in an embodiment in which a duct 34 incorporating the auxiliary valve 17 is housed at the side in a wall of a valve seat 35 of the safety valve. The valve closing member 36 has no duct here. In this embodiment too, the closing element 18 is held open by a laterally arranged rupture-sheet arrangement.

When a rupture sheet has to be replaced in the case of the previously considered designs, it may be that when an intact rupture-sheet is removed and in each case when a new rupture-sheet is put into place, a small amount of the contents of the vessel may escape because, during the removal, the auxiliary valve is still at first open when the rupture-sheet arrangement is detached and is not closed until the rupture-sheet arrangement is being removed and because the auxiliary valve is already pressed into the open position during fitting, before the rupturesheet arrangement is securely screwed down and therefore sealed.

Figure 4 shows how this possible difficulty can be overcome. Here, a push rod 40 is not rigidly connected with the rupture-sheet arrangement but is guided in a projection 41 of an inside clamping plate 43 in an axially displaceable manner, two seals 42 in the form of O-rings being provided for the mutual sealing of the aforementioned components. The axial position of the push rod 40 relative to the rupture sheet arrangement may be adjusted by a set screw 44 and is shown in the screwed down state in Figure 4, so the push rod 40 is therefore in the extended position. In orderto keep the push rod 40 securely in contact with the end of the set screw 44, a spring 45 is provided which urges the push rod, via a collar 46 provided thereon, against the set screw 44.

If a rupture-sheet arrangement/push rod combination of this type is used in one of the previously considered rupture-sheet safety valves, then, before an intact rupture-sheet arrangement is removed from the housing, the set screw is firstly slackened, so that the push rod is retracted and the auxiliary valve is able to close. Now when the rupture-sheet arrangement is removed, not even a small volume of the contents of the vessel will be able to escape.

It is obvious with this arrangement that the fitting is effected at first with the set screw slackened so that when the rupture-sheet arrangement is screwed securely in the housing the auxiliary valve is still not pushed into the open position and the valve is not opened until after the set screw 44 is screwed down in order to open the auxiliary valve.

Figure 5 shows how the push rod 40 can be sealed against the projection 41 by means of a bellows 46.

Figure 6 also shows how, in order to overcome the aforementioned possible difficulty, a small blocking valve 51 can be built into a duct 50 between an end of the duct exposed to the vessel internal pressure, and the auxiliary valve 17. In this embodiment, the blocking valve 51 can be closed before the rupturesheet arrangement 4 is removed, thereby eliminating the risk of a small amount of the vessel contents escaping.

In the embodiments according to Figures 1 and 2, the arresting arms 21 serve to hold the rupture-sheet arrangement in the open position. Figure 7 shows another possibility, a spring 55 being provided here which acts upon the rupture-sheet arrangement 4 in the opening direction. In order to limit the opening stroke, catchers 56 are provided evenly distributed over the periphery. After the rupture-sheet arrange ment has operated, the spring 55 presses the arrangement against the catchers 56 and holds it thus in the open position, even when the discharge of the vessel contents has ceased, so that the auxiliary valve cannot open accidentally. It is thus possible for the contents of the vessel to flow out again unhindered if the safety valve operates again.

The embodiments discussed above are based on the premise that the parameters of the rupturesheet, more particularly the shear circle diameter and its shear strength, determine the response pressure of the rupture-sheet arrangement. In order now to be able to realise the various response pressures without having to prepare special rupturesheets in each case, Figure 8 shows an embodiment in which the rupture-sheet arrangement 4 is under the effect of a pressure spring 60 which acts counter to the opening movement. The other end of the spring 60 bears against a stop plate 61 which is adjustable in the axial direction by means of a threaded spindle 62 and, in this way, it is possible to predetermine the pressing force of the spring against the rupture-sheet arrangement.

In order that the force of the spring 60 does act continuously on the rupture sheet 11, a shoulder 63 is formed on the lower plate 13 and bears on a circumferential stop shoulder 64 co-operating therewith.

In this construction, the rupture-sheet 11 is selected to be thinner than would otherwise be possible and thus has a smaller shear strength than would correspond to the required response pressure, the deficient resistance force to the opening being produced by the spring 60. It is evident that by preselecting the spring force by means of the axial displacement of the stop plate 61, it is possible to select the response pressure of this rupture sheet arrangement.

Thus, the illustrated embodiments of the present invention provide a rupture-sheet safety valve which during undisturbed operation responds at precisely determinable pressures and closes again. Moreover, it is possible to change or replace the rupture-sheet even at the normal operating pressure of the vessel to be safeguarded.

Claims

1. A rupture-sheet safety valve comprising: a valve closing member subjected, in use, to the pressure within a vessel to be safeguarded; a spring biasing the closing member toward its closed position; a rupture-sheet disposed in the discharge direction downstream of the valve closing member, which rupture sheet is clamped abouts its edge; a duct issuing from a point which, in use, is in communication with the interior of the vessel and opening into a space between the valve closing member and the rupture-sheet; and an auxiliary valve located in the duct and mechanically operable by the rupture-sheet to maintain the auxiliary valve in an open position while the rupturesheet is intact.

2. A valve as claimed in claim 1, wherein the auxiliary valve is maintained in the open position against the action of a spring.

3. A valve as claimed in claim 1 or 2 and including a push rod projecting substantially from the centre of the rupture sheet, the free end of the push rod maintaining the auxiliary valve in the open position.

4. Avalve as claimed in claim 3 and including a plate attached to the central region of the rupture sheet, the plate being formed in one piece with the push rod.

5. A valve as claimed in claim 3, wherein the rupture sheet is annular and at its inner edge is clamped between two plates, the push rod being in the form of an extension of a screw clamping the plates together.

6. Avalve as claimed in claim 3, wherein the mechanical connection between the rupture sheet and the auxiliary valve is separate.

7. A valve as claimed in claim 6, wherein the push rod is mounted on an extension of an inner of a pair of clamping plates, the push rod being axially displaceable by means of an externally operable set screw.

8. A valve as claimed in claim 7 and including a spring acting on a collar of the push rod so as to urge the push rod against the set screw.

9. A valve as claimed in claim 7 or 8 and including at least one seal between the push rod and the clamping plate extension.

10. A valve as claimed in claim 9, wherein the seal is in the form of a bellows seal.

11. A valve as claimed in any preceding claim and including a blocking valve located in the duct between the point in communication with the interior of the vessel and the auxiliary valve.

12. A-valve as claimed in any preceding claim and including a spring for holding the rupture-sheet in the open position after the sheet has sheared off, and a catcher limiting the movement ofthe rupturesheet.

13. Avalve as claimed in any one of claims 1 to 11 and including a circumferential projection around the rupture-sheet assembly and arresting arms for co-operating with the projection so as to retain the rupture-sheet assembly in the open position.

14. Avalve as claimed in any preceding claim and including a spring for biasing the rupture sheet assembly towards its closed position.

15. Avalve as claimed in claim 14 and including means for regulating the force of the spring.

16. Avalve as claimed in claim 14 or 15 and including a shoulder provided on the rupture-sheet assembly and engageable with a stop shoulder provided in the valve for limiting the movement of the rupture-sheet assembly under the influence of the spring.

17. Avalve as claimed in any preceding claim, wherein the duct extends in the axial direction of the valve closing member, the rupture-sheet being arranged coaxially with the valve closing member.

18. Avalve as claimed in any one of claims 1 to 16, wherein the duct extends in an angular manner within the valve closing member, the auxiliary valve being arranged in a portion of the duct that is angled relative to the axis of the valve closing member and the axis of the rupture-sheet arrangement being substantially perpendicular to the axis of the valve closing member.

19. Avalve as claimed in any one of claims 1 to 16, wherein the duct passes through the wall of the valve seatforthe valve closing member.

20. A rupture-sheet safety valve substantially as hereinbefore described with reference to, and as shown in, any one of the accompanying drawings.