VENTING ASSEMBLIES FOR FLUID CONTAINERS

Abstract: A venting assembly (1) for a container such as a road tanker comprises a closure member (5), for example a lid member, spring (15) biased into sealing engagement over an aperture (4) for example a filling aperture (4), of the container, and adapted to be displaced upon the internal pressure rising above a certain critical value in emergency conditions to allow gas (6) to escape from the container. Damping means (12) are provided for the closure member (5) and are arranged to prevent opening of the aperture (4) in response to momentary pressure increases to values substantially higher than the critical value, such as may occur in the event of a tanker rolling over, whereby to avoid sudden release of fluid. In an alternative arrangement, the closure member (23) is not damped, and the arrangement is such that the member is urged into a second closed condition (23', 23'') in response to pressure increases substantially higher than the critical value.

Description: Venting assemblies for fluid containers This invention relates to venting assemblies for fluid containers, and particularly but not exclusively to a venting assembly which is associated with the filling aperture of a road tanker. It is known to provide a road tanker with a filling aperture closure assembly wherein, in the closed position, a lid member is spring biased against the aperture so as to prevent spillage of the contents of the tanker therefrom. With such an arrangement, in the event of a potentially dangerous increase in gas pressure within the tanker in an emergency such as a fire, the lid member is urged away from the filling aperture, against the spring bias, allowing the rapid escape of gas from within the tanker. Such emergency venting avoids the risk of an explosion. In a typical such arrangement, the spring biasing of the lid member is chosen such that the critical internal pressure for the release of gas via the filling aperture in an emergency is something in the order of 3.5 psi, and tests show that this form of emergency venting allows extremely rapid gas escape, typically equivalent to 6,000 m per hour, which is very important if safety standards are to be maintained. However, problems can arise with known closure assemblies of this type in the event of the tanker rolling over in a road accident into a condition where the filling aperture is below the level of the liquid within the tanker. In such circumstances, although the pressure on the lid member resulting from the weight of the liquid alone when in a static condition will generally be insufficient to displace the member against the bias of the springs, at the instant of, .and for a period immediately after, OMPI roll over, high pressure surges occur owing to the impact force and to the inertia of the liquid moving within the tanker. The force exerted on the lid member as a result of these surges, during which the pressure may reach 50 psi or more, may be sufficient to cause momentary displacement of the member and opening of the filling aperture. The result of this is that during and following roll over of the tanker, sudden gushes of liquid at a very high pressure, often in the form of a fine spray,, escape from the filling aperture as the lid oscillates between open and closed conditions in response to the sharply fluctuating liquid pressure, and this of course can be extremely dangerous particul- arly in the case of inflammable or toxic substances. It is therefore an object of this invention to provide a venting assembly for a fluid container whereby this disadvantage may be overcome. Viewed from one aspect the invention provides a venting assembly for a fluid container comprising a spring biased closure member effective in use to seal an aperture in said container in the closed condition of said assembly and displaσeable upon the internal pressure rising above a certain critical value to allow gas to escape from wittiin the container, wherein means are provided whereby the closure member is also adapted to seal the aperture upon any momentary increase in pressure to a value substant¬ ially higher than said critical value. Thus, in accordance with the invention, in the context of a movable container such as an oil tanker, the closure member is displaceable to provide emergency venting upon an increase in internal pressure above a certain value, typically approximately 3.5 psi, for example in the event of a fire. However, in the event of tanker roll-over, during any momentary increase in pressure to a value substantially higher than the critical value, e.g. above 8 psi, to the displacement of the liquid within the tanker, the filling aperture is sealed and liquid is prevented from escaping. The manner in which the closure member is adapted to seal the aperture both under normal circumstances in the closed condition, and in the event of a momentary increase of pressure in the event of a tanker rolling over, may vary. In one preferred arrangement damping means are provided for the closure member such that displacement of the closure member only occurs if the internal pressure remains above the critical value for longer than a certain response time of the member, for example 2 seconds. The response time is chosen so as to be longer than the length of the high pressure surges which may be expected in the event of a tanker rolling over, and thus the closure member is not displaced from its sealing condition in response to such surges. Experience shows that the high pressure surges which may occur are in fact extremely short lived and are in the order of milliseconds. In the event of a fire, however, the internal pressure quickly rises to and remains at values greater than the critical value, whereupon emergency venting will occur after the response time has lapsed, i.e. within a matter of a few seconds. In such an arrangement, the closure member advantageously constitutes a lid member of a filling aperture of the container and in the closed condition of the assembly is spring biased into sealing engage¬ ment with a peripheral wall defining said aperture. The lid member may be carried by a cover arm, and the biasing springs for the lid member preferably act therebetween. The cover arm may be pivotably mounted so as to enable manual opening of the aperture for filling purposes, means being provided to lock the arm in a closed condition. Alternatively the closure member may be associated with an aperture separate from the filling aperture. The damping means for the closure member preferably comprises a dash pot, i.e an oil filled cylinder having a piston disposed therein which includes a restricted orifice such that relative movement between the piston and the cylinder may only occur upon the oil being forced through the orifice. Where the closure member is carried by a cover arm as discussed above, the dash pot preferably acts therebetween, and in a preferred embodiment the cylinder is secured to or forms part of the closure member and the piston extends from and - is fixedly secured to the cover arm. In an alternative arrangement the closure member is not damped, but rather means are provided whereby in response to any increase in pressure (not only of a momentary nature) which is substantially higher than the critical value for emergency venting, typically any increases above approximately 8 psi, the closure member is displaced further into a second condition where sealing of the aperture is also effected. Thus, in the event of an increase in internal pressure to values above the critical value the closure member is displaced such that emergency venting occurs? however, upon increases in pressure to values substantially higher than the critical value such as may occur in the event of a tanker rolling over, the closure member is displaced further against the spring biasing into its second sealing condition such that liquid is prevented from escaping. In a preferred such arrangement the closure member is movable between the apertured side walls of a housing. In the normal, closed condition, the closure member is spring biased against an inner one of the side walls so as to seal the aperture or apertures therein and thereby prevent spillage O PI from the container via the apertures. In the event of an increase in internal pressure to above the critical value, e.g. above 3.5 psi the closure member is displaced against the biasing springs away from the inner wall, and emergency venting occurs since gas can escape via the housing. Maximum venting preferably occurs at approximately 5 psi. However, in the event of the high pressure surges which can occur following a tank rolling over, the increased force on the closure member causes it to be further displaced outwardly against the spring biasing such that at e.g. 8 psi it engages the outer wall of the housing and seals the aperture or apertures therein thus preventing fluid leakage. In this embodiment it will be seen that the biasing -force of the springs must be carefully selected such that on the one hand emergency venting occurs in response to pressures which might be expected in the event of a fire, while on the other hand the closure member is displaceable into its second sealing condition in response to the higher pressures occuring in the event of a tanker rolling over. With such an arrangement, it will be appreciated that a very small amount of leakage may occur as the closure member is displaced into its second sealing condition, although such leakage will be minimal. In a preferred embodiment the outer wall of the housing forms part of a lid member for the filling aperture of the container which is sealingly engageable with a peripheral wall defining the aperture in the closed condition of said assembly. As in the alternative embodiment discussed above the assembly preferably includes a pivotably mounted cover arm which carries the lid member and housing and is lockable in the closed condition. Alternat¬ ively, as before, the closure member may be associated with an aperture separate from the filling aperture. As is conventional, a closure assembly in accordance with the invention may additionally be provided with a breather valve adapted to maintain the interior of the container within desired pressure and vacuum limits and to accommodate small changes in pressure due to changes in temperature in non- emergency conditions. In the embodiment discussed above incorporating a dash pot, the breather valve may convenientl * y be mounted in a common assembly with the dash pot, and in a preferred such embodiment the breather valve includes an annular closure member mounted σoaxially with and surrounding the dash pot cylinder, the closure member being arranged to prevent release of fluid via the breather valve in emergency conditions. Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side elevation, partly in cross- section, of a venting assembly; Figure 2 illustrates on an enlarged scale the assembly of Figure 1 in the emergency venting condition; Figure 3 is a view similar to Figure 1 illustrat- ing an alternative embodiment of venting assembly; and Figure 4 illustrates part of a modified version of the embodiment shown in Figure 1. Referring firstly to Figure 1, a venting assembly 1 is associated with a filling aperture 4 of a road tanker (not shown) and includes a base plate 2 which is secured in use to an upper wall of the tanker and which includes a neck portion 3 extending around the outer periphery of the aperture 4. A cover arm 6 carrying a closure member in the form of lid member 5 is pivotably mounted to the base plate 2 and suitable latch means 7 are provided such that the assembly may be locked in the closed condition shown in Figure 1 and , upon release of the latch means 7, the assembly of cover arm 6 and lid member 5 may be pivoted in the direction of the arrow A so as to open the aperture 4 for 5 filling purposes. As is conventional, the lid member 5 carries a breather valve in the form of a pressure/vacuum breather vent 8 which will not be described in detail but which is effective to maintain the internal pressure of the tanker at 10 a desired value and to accommodate slight changes in pressure due to temperature variations under normal conditions. The lid member 5 is secured to the cover arm by means of a piston rod 9 the upper end of 15 which extends through a central aperture in the member 5 and is retained by means of a nut 10 and- a collar 20. Secured to or integral with the lower end of the piston rod 9 is a piston 11 which forms part of an oil filled dash pot 12 the cup-shaped 20 cylinder 13 of which is formed integrally with the lid member 5. An annular piston rod guide 14 is threadedly engaged in the upper part of the cylinder 13, and biasing springs 15 act between the cover arm 6 and the lid member 5. In the open 2.5 condition of the assembly, engagement at the lower end of the piston rod between an upper part 16 of the piston 11 and the piston rod guide 14 and, at the upper end, between the nut 10 and the cover arm, holds the cover arm and lid member together 30 against the biasing effect of the springs 15. The depth to which the piston rod guide 14 is screwed down into the cylinder is chosen such that when the latch means is locked in the fully closed condition of the assembly as shown in Figure 1 the nut 10 5 becomes upwardly slightly spaced from the surface of the cover arm, and therefore in this position the springs 15 are effective to urge the lid member 5 firmly against the neck 3 such that the 4 is tightly sealed be means of a resilent sealing member 17 secured to the lid member. As shown in Figure 2, in the event that the pressure within the tanker rises above a certain critical value, for example 3.5 psi such as may occur during a fire, the lid member is displaced upwardly against the spring biasing to allow the rapid escape of gas from inside the tanker, as shown by the arrow G. However, as the lid is raised, the cylinder 13 of the dash pot moves relative to the piston 11, which is restrained from moving upwardly by the collar 20, and this causes oil to be forced through a narrow orifice 21 in the piston 11 thus imparting a delay of for example two seconds between an increase in internal pressure above the critical value and raising of the lid sufficiently to permit emergency venting. While such a delay in the order of seconds does not represent a reduction in safety in the event of a fire, it is sufficient to prevent unwanted opening of the aperture and the release of fluid owing to. high pressure surges which can occur should the tanker roll over, which surges are considerably shorter than the response time of the lid member. In a modified arrangement, the orifice 21 may comprise or be replaced by a suitable valve means adapted to provide suitable flow resistance in the opening direction to impart the required delay, but providing lesser resistance in the opposite sense whereby to ensure that the lid can close fully if the internal pressure returns to a normal value, Referring now to Figure 3, an alternative embodiment of venting assembly is illustrated. In this embodiment a lid member 24 is fixedly secured to the cover arm 6 by means of a shaft 25 which threadedly receives a nut 26 at its upper end; a suitable spring loading 27 is provided between the cover arm 6 and the lid member 24 such that φJ A OMPI in the closed position a peripheral resilient sealing member 28 secured to the lid member is tightly clamped against the neck portion 3 such that the aperture is sealed. The lid member 24 also forms one side wall of a housing 29 in which is disposed a closure member 23 slidably mounted to the lower part of the shaft 25. As illustrated, in the closed position the closure member 23 is biased by springs 35 extending between the cover arm 6 and the member 23 through apertures 32 in the lid member so that the closure member engages a peripheral sealing member 30 extending around an aperture 31 in the lower side wall of the housing such that a seal is effected. In the event of a fire, the rise in internal pressure above a certain critical value, for example 3.5 psi, causes the closure member to be displaced upwardly such that gas can escape from the tanker via the opening 31 formed in the lower wall of the housing and the openings 32 formed in the lid member 24. The spring biasing is preferably such that when the internal presure reaches 5.2 psi the member is in a position 23' midway between the side walls such that maximum venting occurs at that pressure. However, in the event of the • internal pressure increasing to values which are substantially higher than the critical value, for example above 8 psi as may occur when a tanker rolls over, the closure member 23 is further displaced upwardly against the biasing of the springs 35 so that it engages a peripheral sealing member 36 secured to the underside of the lid member, as shown in broken lines by reference numeral 23". In this position the filling aperture is once again sealed since the flow of gas or liquid though the apertures 32 in the lid member is cut off, and thus the escape of liquid during or after a tanker rolls over is minimised. It will be that a small amount of liquid may be released as the closure member is displaced in response to a surge of high fluid pressure from position 23' to position 23"; howevever, in practice the response time of the member 23 is sufficiently rapid for the volume of liquid which escapes to be minimal. Finally, Figure 4 illustrates a modified version of the lid member assembly shown in Figure 1 in which a breather valve 40 is mounted in a common assembly with the dash pot 12. The valve 40 comprises a housing 41 surrounding the dash pot cylinder 13, and an annular closure member 42 formed e.g. from nylon with a rubber sealing disc 43 on its upper surface. A coil spring 44 acts between the member 42 and the base of the housing 41. Under normal operating conditions, the weight of the closure member 42 overcomes the upward biasing force of the spring 44 and therefore, as shown on the left hand side of Figure 4, the member sits on a ledge 45 provided on the peripheral wall of the cylinder 13. In this position t venting of the container occurs via ports 46, 47 provided in the peripheral wall of the housing 41 and in the lid member 5. However, in the event of the tanker railing over, the downwards force decreases and the action of the spring is then effective to urge the closure member 40 into sealing engagement with ports 47, as shown in the right hand side of Figure 4. Thus, leakage through the breather valve in the event of an emergency is avoided.

Claims: CLAIMS: 1. A venting assembly for a fluid container comprising a spring biased closure member effective in use to seal an aperture in said container in the closed condition of said assembly and displaceable upon the internal pressure rising above a certain critical value to allow gas to escape from within the container, wherein means are provided whereby the closure member is also adapted to seal the aperture upon any momentary increase in pressure to a value substantially higher than said critical value. 2. A venting assembly as claimed in claim 1 wherein damping means are provided for the closure member and arranged such that displacement of the closure member only occurs if the internal pressure remains above the critical value for longer than a certain response time of the member. 3. A venting assembly as claimed in claim 2 wherein the closure member constitutes a lid member of a filling aperture of the container which, in its closed condition, is spring biased into sealing engagement with a peripheral wall defining the aperture. 4. A venting assembly as claimed in claim 2 or 3 wherein said damping means comprises a dash pot. 5. A venting assembly as claimed in claims 3 and 4 wherein the closure member is carried by a cover arm of the assembly and the dash pot acts therebetween, the cylinder of the dash pot being fixedly secured to the closure member and the piston thereof being coupled to the cover arm. 6. A venting assembly as claimed in claim 4 or 5 further comprising a breather valve, such valve being mounted in a common assembly with the dash pot and comprising an annular closure member mounted coaxially with and surrounding the dash pot cylinder, the closure member being arranged to prevent release of fluid via the breather valve in emergency conditions. 7. A venting assembly as claimed in claim 1 wherein means are provided whereby in response to any increase in pressure which is substantially higher than the critical pressure the closure member is displaced further against the spring biasing into a second condition where sealing of the aperture is also effected. 8. A venting assembly as claimed in claim 7 wherein the closure member is mounted within a housing having apertured side walls between which the closure member is movable. 9. A venting assembly as claimed in claim 8 wherein an outer one of the side walls of said housing forms part of a lid member for a filling aperture of the container. 10. A road tanker incorporating a venting assembly as claimed in any preceding claim. 11. A venting assembly substantially as herein described with reference to the accompanying drawings.

Inventors: STOW JOHN RONALD, STOW, JOHN, RONALD
Applicants: EMCO WHEATON, EMCO WHEATON U. K. LIMITED
Application year: 1984
Main classification: B65D90
IPC codes: B65D90