Fluid handling – Destructible or deformable element controlled – Destructible element
Reexamination Certificate
2000-03-16
2001-09-11
Buiz, Michael Powell (Department: 3753)
Fluid handling
Destructible or deformable element controlled
Destructible element
C137S072000, C137S079000
Reexamination Certificate
active
06286536
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application Serial No. 199 11 530.3, filed Mar. 16, 1999, the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a safety device for an apparatus under gas or vapor pressure such as a vessel, in particular for use in road vehicles.
Regulations require that vessels under gas pressure should safely withstand expected loads during operation. Moreover, safety devices, such as flow rate limiters and safety devices to protect against excess pressure are required in case of fire. According to technical standards for pressure gases TRG 381, vessels under gas pressure should be equipped with a fuse-type safety device or equivalent safety device to prevent excess pressure in case of fire and thereby protect against rupturing of the vessel. Larger vessels require application of several such trigger units, to ensure a sufficient pressure relief.
The use of fuse-type safety devices suffers, however, shortcomings because the employed solders are fairly expensive and progressively deform plastically over time when subject to a continuous load. Thus, so-called creeping, leads to an alteration of the response characteristic of the safety device, so that the condition of the fuse-type safety device cannot be assessed from outside.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an improved safety device for an apparatus under pressure, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved safety device for a vessel under gas pressure, which has an improved response characteristic and yet has a compact configuration.
These objects, and others which will become apparent hereinafter, are attained in accordance with one aspect of the present invention by providing a thermal trigger unit which includes a rupture element, and a closure member moveable from a ready position, in which the closure member is so acted upon by the rupture element that a guide shaft of the closure member projects into and seals an overflow channel from an outlet port of the housing, to a release position, in which the overflow channel is cleared for fluid communication with the outlet port.
The rupture element exhibits a rapid response characteristic when exposed to heat and is not subject to any plastic deformations. Therefore the closure member is securely held in place, and creeping, as encountered with solders, is eliminated. The response characteristic of the safety device thus remains substantially constant over time.
Suitably, the closure member is sealed about its circumference with respect to the overflow channel, for example, by sealing elements in the form of O-rings.
According to another feature of the present invention, the closure member includes a support plate which is wider than the guide shaft, so that the closure member has a substantially T-shaped configuration, thereby axially securing the closure member in place. The support plate is pressed in tight contact against a housing area that surrounds the overflow channel, so that the overflow channel is fluidly sealed in conjunction with incorporation of a sealing element. Certainly, the sealing element may also be disposed in a transition zone between the guide shaft and the support plate. The sealing element may be supported in the housing as well as in the closure member.
When exposed to heat, the rupture element bursts and the closure member is displaced from the overflow channel, as a consequence of the interior pressure in the vessel, acting against the proximal end face of the guide shaft. Thus, gas can escape the vessel through the overflow channel and the cleared outlet port.
According to another feature of the present invention, the closure member may interact with the rupture element and at least one restraining member, so that the pressure force, generated by the interior pressure in the vessel and applied against the end face of the closure member, will not act solely on the rupture element but is also transmitted onto at least one restraining element. Suitably, the rupture element and the restraining element are fixed in place on a shaft-distal side by an abutment plate. Advantageously, one rupture element and two restraining elements are provided and placed in a circular arrangement at an angular distance of 120°. In this manner, when the rupture element bursts upon exposure to heat, only the restraining elements remain to interact with the closure member. The closure member can be pushed out of the overflow channel by the inner vessel pressure which is applied in the overflow channel, thereby establishing a fluid communication to the outlet port. A reduction of the force applied on the rupture element enables the use of smaller rupture elements that are quicker to respond.
Suitably, the abutment plate is so supported in the housing as to permit a tilting movement thereof so that the restraining elements, positioned between the abutment plate and the closure member, allow a jam-free displacement of the guide shaft from the overflow channel.
According to another feature of the present invention, the housing has an open top which is closeable by a lid, whereby a central coupling member is incorporated as abutment between the abutment plate and the lid. The coupling member may have a spherical surface so as to establish a single-point bearing for the abutment plate in the housing, and to allow freely swingable movement of the abutment plate. The trigger unit is secured in the housing via the lid, which may be designed as screw cap. Suitably, the coupling member is arranged at a central location so as to prevent interference with the rotary movement of the lid, when being threaded into position upon the housing. The coupling member can be configured in many different ways. However, a point contact with the abutment plate is preferred. Apart from a substantially spherical configuration, the coupling member may also have a conical configuration of cylindrical configuration.
According to another embodiment of the present invention, the overflow channel is subdivided in three passageways of different diameters. A first one the passageways is positioned distal to the pressure vessel and receives the guide shaft of the closure member. This passageway has a smallest diameter so that only small forces act on the rupture element which is secured to the closure member. Extending axially inwardly of the first passageway is a second, central passageway which has a greatest diameter and sealingly guides a differential piston which is loaded by a spring in the direction of the vessel and formed interiorly with a longitudinal channel. The differential piston has a sealing stub for engagement in a third one of the passageways positioned adjacent the gas pressure vessel. Thus, the differential piston is sealingly guided in the third passageway as well as in the central passageway. When the rupture element bursts, the closure member clears the upper, first passageway of the overflow channel, so that gas can escape from the central passageway of the overflow channel through the upper passageway, whereby no gas can flow through the longitudinally channeled differential piston for neutralizing the pressure drop. The differential piston is so sized that the vessel-confronting sealing stub is acted upon by a sufficiently high static and dynamic pressure to displace the differential piston in opposition to the spring force in the direction of the first passageway. In this manner, the fluid communication between the housing outlet port and the central passageway is cleared for escape of gas. As a consequence of the small diameter of the vessel distal passageway of the overflow channel, forces acting on the rupture element are independent from the cross section of the other passageways. Thus, it is possible, to use small rupture elements which are quick to respond, while at the same time realizing high flow rates
Kamp Franz
Rottger Konstantin
Buiz Michael Powell
Feiereisen Henry M.
Krishnamurthy Ramesh
VTI Ventil TechnikGmbH
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