GB2148115A

GB2148115A - A fastening arrangement

Info

Publication number: GB2148115A
Application number: GB8404061A
Authority: GB
Inventors: Roger Carr
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-10-21
Filing date: 1984-02-16
Publication date: 1985-05-30
Also published as: GB2148115B; GB8328199D0; GB8404061D0

Abstract

A cap 10 is fastened in the neck 12 of a pressure vessel such as a fire extinguisher by a fastening arrangement which makes use of a key with two parallel arms and which is inserted laterally through two parallel passages 16, 18 through the neck, to prevent axial movement of the cap relative to the neck. <IMAGE>

Description

SPECIFICATION A fastening arrangement Field of the Invention The invention relates to a fastening arrangement for fastening a first object in a neck of a second object. A typical application is the fastening of a head fitting, or cap, in the neck of a fire extinguisher casing. The invention also has particular suitability to use in connection with pressure vessels generally. The invention also relates to a fire extinguisher.

Background to the Invention It is known to fasten a first object in the neck of a second object by using a screw-threaded joint between them. This type of joint is expensive to manufacture and, unless a separate pressure relief valve is provided, unscrewing a cap subjected to pressure from below can be dangerous.

It is necessary to provide considerable mechanical strength to joints of this sort, both to resist any pressure tending to separate the objects and also to allow any seal between the objects to be held stably in position.

Summary of the Invention According to the present invention, there is provided a fastening arrangement for fastening a cap within a neck of a pressure vessel, wherein two parallel slots are provided in each of the cap and the neck such that when the cap is assembled within the neck, two parallel passages exist through the assembly, the passages extending symmetrically relative to a centre line of the neck, the arrangement including a fastening member having two parallel arms rigidly joined together at one end and adapted to extend one along each of the passages to prevent relative axial movement between the objects.

Locking means can be provided to prevent accidental or unauthorised withdrawing of the member.

The fastening member may be a single key with arms which extend right through the passages. In this case, the locking means can attach to a free end of one (or both) arms. Alternatively, the fastening member can be two keys each of which has arms extending part of the way along each passage, the ends of the arms engaging with one another in the middle of the passages to prevent accidental withdrawal.

This fastening arrangement lends itself to combination with a pressure relief valve, and accordingly the fastening arrangement may include a pressure relief valve which is held closed by the fastening member, but which opens as soon as the fastening member is moved in the direction of withdrawal, to release pressure inside the vessel before the fastening between the cap and the vessel is released.

The pressure relief valve may be spring loaded into a closed position, with a plunger which, in the closed position protrudes into one of the passages through the cap/vessel assembly, and which can be depressed to open the valve on movement of an arm of a fastening member.

The invention extends to a fire extinguisher in which the cap and the pressure vessel are held together by an arrangement as set forth above.

The fastening member may include holes for receiving coloured indicating pegs which indicate the condition of the extinguisher.

Brief Description of the Drawings The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded view of the neck of a pressure vessel and a cap therefor; Figure 2 is a plan view of a fastening member; Figure 3 is a section through a portion of the cap of Figure 1; Figure 4 is a section through the fastening member of Figure 3 on the line IV-IV; Figure 5 is a perspective view of part of the cap shown in Figure 2, illustrating an alternative form of fastening in accordance with the invention; and Figure 6 is a view, corresponding to Figure 2, of an alternative form of fastening member.

Description of Preferred Embodiments In Figure 1, a cap 10 is shown above a neck 12 of a pressure vessel 14 into which it is to be fitted. The vessel can for example be a fire extinguisher. A seal (not shown), such as an O-ring, will be provided between the cap and the neck to make this pressure tight.

The cap has two opposite grooves 16 in its circumference. These grooves are bounded by surfaces which lie on parallel chords. The neck has two pairs of rectangular openings 18 through its wall. Lines joining the openings of each pair would lie on chords parallel to those bounding the surfaces of the grooves 16.

When the cap 10 is placed in the neck 12, a flange 20 lies on top of the neck. The flange includes a lug 22 which fits into a recess 24 on the neck to ensure that the cap is correctly oriented on the neck with the grooves 16 lining up with the openings 18.

A fastening member 26 is used to secure the two parts together. The member has two parallel arms 28 joined together by a shoulder 30. To secure the joint between the assembled cap 10 and neck 12, the arms 28 are pushed into the openings 18 on one side until they project out of the openings on the other side of the neck 12. In Figure 2, the neck 12 is indicated in dotted lines. The part of the shoulder 30 that lies adjacent the neck is shaped so as to fit snugly against the neck. To guard against accidental or unauthorized withdrawal, a lock or a seal which is unable to pass through the openings 18 can be fixed in an opening 32 at the end of one arm 28. This arrangement, whilst being very simple to manufacture and to install, provides excellent support for the cap in the neck.The cap is supported against the neck at four points arranged roughly equidistantly around the neck, by the substantial arms of the fastening member.

Fire extinguishers are a particular class of pressure vessels to which this type of fastening can be applied. Fire extinguishers have to be serviced regularly to maintain their efficiency, and the type of fastening described makes it easy to remove and reassemble the head cap. Some pressure vessels of fire extinguishers are not pressurised until the extinguisher is operated. However, it does happen that, for one reason or another, the vessel is pressurised at service time. It then becomes dangerous for the service engineer to open the vessel and this applies also to permanent pressure vessels.

To deal with this problem, a pressure relief valve 34 is provided in the cap 10. This valve is shown in Figure 3 and has a valve plunger 36 with an O-ring seal 38 which seats inside a bore 40. A spring 42 normally keeps the valve closed, preventing pressure from escaping.

The plunger 36 has a domed top end which projects into a groove 16 of the cap. When the fastening member 26 is inserted in the groove, the plunger will be depressed thus opening the valve.

However, as can be seen in Figures 2 and 4, one arm 28 of the fastening member is provided with a hole 44 with chamferededges. This hole is positioned so as to register with the plunger 36 when the fastening member is fully inserted. The plunger is thus able to rise to close the valve in this position.

However, if the fastening member is withdrawn Slightly, the chamfered edges of the hole 44 will act a,s a cam to depress the plunger as the arm 28 moves. The size and position of the hole are preferably chosen so that the valve is opened before the free ends of the arms 28 disengage from the openings 18 on the far side of the neck. In this way, all pressure will be released from the vessel before the mechanical joint between cap and vessel is disturbed. The cap can then be safely removed.

Figures 3 and 5 show an alternative form of the fastening arrangement. These Figures show the pressure relief valve which is mounted in a cylindrical housing 46 on the cap. An abutment 48 is fitted at the bottom of this housing to support the spring 42 and to take up the reaction forces when the spring is compressed. The abutment has a central bore 50 so that the gas can flow past it. To hold this abutment in place against axial forces, parallel grooves 52 are formed at opposite sides of both members. Fastening members 54 are inserted from opposite sides. The arms of these fastening members do not extend right across the joint, but meet in the middle. To prevent them accidentally falling out, they have ends 56 which are shaped so that when the arms are pushed against one another, they engage and hold each other in place.

This arrangement is secure, easy to assemble and cheap to produce in that no accurate machining is required.

The alternative form of fastening member shown in Figure 6 incorporates a facility for indicating externally the service record and the discharge test record of the extinguisher to which it is applied. In Figure 6, the same reference numerals as in Figure 2 are used to denote equivalent parts.

The shoulder 30 has two ears 60 and 62. One of these ears 60 has a shaped hole 64, and a christmas tree plug 66 can be put in this hole. The colour of the plug will indicate the discharge test record of the extinguisher. The plug cannot be withdrawn without destroying it, and thus cannot be tampered with without leaving evidence of the tampering.

Similarly, the opening 32 can be provided with a second christmas tree plug 68. The colour of this plug can be used to indicate the service record of the extinguisher, and of course this plug also continues to function as a safety lock, preventing unauthorised withdrawal ofthefastening member.

Claims

1. Afastening arrangement for fastening a cap within a neck of a pressure vessel, wherein two parallel slots are provided in each of the cap and the neck such that when the cap is assembled within the neck, two parallel passages exist through the assembly, the passages extending symmetrically relative to a centre line of the neck, the arrangement including a fastening member having two arms rigidly joined to one another at one end and adapted to extend one along each of the passages to prevent relative axial movement between the cap and the neck.

2. A fastening arrangement as claimed in Claim 1, wherein locking means are provided to prevent accidental or unauthorised withdrawing of the member.

3. A fastening arrangement as claimed in Claim 1 or Claim 2, wherein the fastening member is a single key with arms which extend right through the passages.

4. A fastening arrangement as claimed in Claim 3, when dependent on Claim 2, wherein the locking means can attach to a free end of one (or both) arms.

5. A fastening arrangement as claimed in Claim 1 or Claim 2, wherein the fastening member comprises two keys each of which has arms extending part of the way along each passage, the ends of the arms engaging with one another in the middle of the passages to prevent accidental withdrawal.

6. A fastening arrangement as claimed in any preceding claim, and including a pressure relief valve which is held closed by the fastening member, but which opens as soon as the fastening member is moved in the direction of withdrawal, to release pressure inside the vessel before the fastening between the cap and the vessel is released.

7. A fastening arrangement as claimed in Claim 6, wherein the pressure relief valve is spring loaded into a closed position and has a plunger which in the closed position protrudes into one of the passages through the cap/vessel assembly, and which can be depressed to open the valve on movement of an arm of a fastening member.

8. A fastening arrangement substantially as herein described with reference to any one embodiment shown in the accompanying drawings.

9. A fire extinguisher in which the cap is held in the cylinder by a fastening arrangement as claimed in any preceding claim.

10. Afire extinguisher as claimed in Claim 9, wherein the fastening arrangement is as claimed in Claim 2, wherein the locking means is an opening at the end of one of the arms of the fastening member, and wherein a peg which cannot be removed from the hole without breaking is placed in the hole.

11. A fire extinguisher as claimed in Claim 10, including a second opening in the fastening member, for receiving a peg which cannot be removed without breaking.

12. A fire extinguisher as claimed in Claim 10 or Claim 11, in combination with a set of pegs of different colours, the pegs being adapted to fit into the openings in the fastening member and to be impossible to remove without destroying the peg.

13. Afire extinguisher substantially as herein described, with reference to any one embodiment shown in the accompanying drawings.