GB2139888A - Flame arrester - Google Patents

Abstract

A flame arrester suitable for vent-pipes which has a cover protecting the element. The cover is mounted to one side of the flame arrester body by a leaf spring, whilst the other side of the cover is held by a heat fusible linkage to the body. On ignition of vapour on the exterior of the element, the linkage parts and the cover swings away under the influence of the leaf spring. <IMAGE>

Description

SPECIFICATION Flame trap or flame arrester This invention relates to flame traps or flame arresters. These devices are designed to stop the unrestricted propagation or spread of flame through flammable gas or vapour mixtures in pipelines. They prevent flame from entering or leaving plant and can confine the passage of flame to certain equipment.

When a flame trap is mounted on eg a vent pipe, it is typically arranged vertically, so that the flame trap element would be exposed to dust and the weather if it were not protected by a cover.

The employment of such covers does however lead to a particular problem with flame traps. When gas or vapor mixtures ignite, eg from a lightning strike, on the outward side of the flame trap, propagation of the flame back into the vent pipe or pipeline is prevented by the flame trap element absorbing and dissipating heat from the burning gas or vapour. This is achieved as the hot gases give up their heat to the cell walls as they pass through the metal flame trap element. With the use of a cover however, the heat generated by the flame may be conducted through the element and cause reignition on the other side of the element, which is effectively a failure of the flame trap. Alternatively, the heat may cause distortion of the element which permits the flame front to pass back through the element.

This deterioration in flash-back resistance is particularly a problem with low flows of vapour through the trap.

The only apparent way to significantly reduce this problem with the use of covers is to remove the cover from the flame trap before heat can damage the element, and thereby permit improved heat dissipation from the flame.

According to the invention we provide a flame trap or arrester comprising a body carrying a flame trap element, said body being adapted at one end to be connected to a line from which flammable vapours or gases may emanate, and a cover mounted on the end of the body remote from the line, said cover being connected to the body at one side by resiliant means and at a spaced position from the resilient means by a linkage which at normal operating temperatures is adapted to hold the cover in position against the action of the resilient means, but which is broken at higher temperatures resulting from the incidence of burning vapours, thereby resulting in the cover being sprung away from the end of the body.

The flame trap is typically generally cylindrical in shape with a circular removable element employed.

The linkage preferably comprises a heat-fusible solder or adhesive, such solder or adhesive being selected for any particular application according to the temperature at which it melts. The linkage is preferably connected to the body at a position diametrically opposite the resiliant means. The linkage may comprise a unit which is releasably secure to the body eg by means of a threaded bolt, and the cover may be releasably secured to the linkage to permit inspection of the element without damaging the linkage.

The resilient means may be in the form of a leaf spring, and preferably the curved portion ofthe leaf spring (when it is in its compressed condition) is adjacent the end of the leaf which is attached to the body. This feature permits the active part of the leaf spring to be relatively unaffected by hot gases emanating from under the cover when the trap is mounted substantially vertically, since the hot gases will rise on leaving the perimeter of the cover. The spring should be sufficiently long to enable its curved portion to be spaced from the perimeter of the cover to ensure that hot gases do not impinge directly on the curved portion.

The cover is preferably of generally U-shaped cross-section with the sides of the U spaced from the body. The linkage between the cover and the body may be located inwardly from the sides of the U and be secured in an end face of the body. The means for releasably securing the linkage to the body may also be employed as one of a plurality of means for holding the element in place within the body eg by means of a washer overlapping the end of the element, said washer being held in place by a threaded bolt which holds the linkage to the body.

The present invention will now be described, by way of example only, with reference to the accompanying drawings of which Figure 1 is an end elevation of a flame trap according to the invention, and Figure 2 is a side elevation partly in cross-section of the flame trap of Figure 1.

The flame trap or arrester comprises a body 10 with flanges 11 adapted to be connected to mating flanges (not shown) on a vertical vent line. Body 10 is generally cylindrical and its inside wall is stepped to provide location for a flame trap element 12. Element 12 is typically cylindrical and is of crimped metal construction which is designed to prevent a flame on the side of trap remote from the line from passing back into the line.

A cover 13 is provided to the trap to minimise the likelihood of blockage or deterioration of the element 12 by dust or weather conditions. Cover 13 is in cross-section of inverted U-shape and extends beyond the perimeter of the trap so as to permit the escape of vapour or hot gases resulting from a flame around the perimeter of the cover 13.

Element 12 is held in place partly by two bolts 14 entering the end face 15 of body 10 which have washers 16 which overlap the perimeter of the element 12. The position of bolts 14 is seen more clearly in Figure 1 where they are shown in dashed outline.

A leaf spring 17 is attached to the cover 13 at one end and to body 10 at the other. Leaf spring 17 has a straight portion adjacent the cover 13, and a curved portion 18 located adjacent the body end of the spring 17. In its compressed condition spring 17 acts in a direction to tend to remove the cover 13 from the end of the trap.

Diametrically opposite spring 17 is a linkage 19 which is held into the end face 15 of body 11 by means of bolt 20. Bolt 20 also secures washer 21 which overlaps the perimeter of the element 12 and serves a third means for holding element 12 in place.

Linkage 19 comprises a rod 22 held to bolt 20 by heat-fusible solder or adhesive, suitably selected for the particular application, which will melt at a predetermined temperature and thereby permit cover 13 to be removed from the end of the trap under the action of leaf spring 17. The cover 13 will however remain attached to leaf spring 17 and therethrough to body 11 and can be put back in place by the provision of a replacement linkage. The linkage 19 is secured to the cover 13 by a wing-nut 23 and a co-operating thread on rod 22 which permits cover 13 to be separated manually from the linkage 19 to permit inspection of the element and/or the spring 17.

Claims (12)

1. A flame trap or arrester comprising a body carrying a flame trap element, said body being adapted at one end to be connected to a line from which flammable vapours or gases may emanate, and a cover mounted on the end of the body remote from the line, said cover being connected to the body at one side by resiliant means and at a spaced position from the resilient means by a linkage which at normal operating temperatures is adapted to hold the cover in position against the action of the resilient means, but which is broken at higher temperatures resulting from the incidence of burning vapours, thereby resulting in the cover being sprung away from the end of the body.

2. Aflame trap or arrester as claimed in Claim 1 which is generally cylindrical in shape with a circular removable element.

3. A flame trap or arrester as claimed in Claim 1 or Claim 2 in which the linkage comprises a heatfusible solder or adhesive, such solder or adhesive being selected according to the temperature at which it melts.

4. A flame trap or arrester as claimed in any preceding claim in which the linkage is connected to the body at a position diametrically opposite the resiliant means.

5. A flame trap or arrester as claimed in any preceding claim in which the linkage comprises a unit which is releasably secured to the body.

6. A flame trap or arrester as claimed in any preceding claim in which the cover is releasably secured to the linkage so as to permit inspection of the element without damaging the linkage.

7. A flame trap or arrester as claimed in any preceding claim in which the resilient means is in the form of a leaf spring, the curved or active portion of which, when it is in its compressed condition, is adjacent the end of the leaf which is connected to the body.

8. A flame trap or arrester as claimed in Claim 7 in which the spring is sufficiently long to enable its curved or active portion to be spaced from the perimeter of the cover such that hot gases do not impinge directly on to the curved or active portion.

9. A flame trap or arrester as claimed in any preceding claim in which the cover is of generally U-shaped cross-section with the sides of the U spaced from the body.

10. A flame trap or arrester as claimed in Claim 9 in which the linkage between the cover and the body is located inwardly from the sides of the U and is secured in an end face of the body.

11. A flame trap or arrester as claimed in Claim 6 in which the means for releasably securing the linkage to the body is employed as one of a plurality of means for holding the element in place within the body.

12. A flame trap or arrester as hereinbefore described and as shown in the accompanying drawings.