Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
1998-12-01
2001-02-20
Larkin, Daniel S. (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S046000, C340S605000
Reexamination Certificate
active
06189369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a casing, in which a gas container is to be accommodated, i.e. a cylinder cabinet. More specifically, the present invention relates to a gas leakage detecting apparatus provided with such a cylinder cabinet.
2. Description of the Prior Art
A special material gas for use in the manufacture of semiconductors is usually used as stored in a portable gas container which is called a gas bomb or gas cylinder. As to such special material gases for use in the manufacture of semiconductors, there are many dangerous gases having combustibility (explosiveness), toxicity, corrosiveness or combustion-supporting properties, and hence they must be given with thoughtful consideration in safety when used. Accordingly, a gas container filled with a dangerous special material gas has been hitherto accommodated in a casing, which is referred to as a cylinder cabinet, thereby coping with an unforeseen gas leakage.
The cylinder cabinet itself functions as a closed box for preventing a gas from spreading to the atmosphere, the inside of which is normally ventilated so that a leaked gas can be diluted and exhausted. Its design is such that air is taken in by an air take-in port in the lower portion of the cylinder cabinet and the same air is discharged to the atmosphere through an exhaust duct in the upper portion thereof. Furthermore, said exhaust duct has a gas leakage detecting apparatus connected thereto, whereby it is possible to monitor for leaked gas.
Although one is obligated to carry out normal exhaust in a cylinder cabinet in accordance with the related laws, it is very important for safety reasons that such normal exhaust is carried out at a proper ventilation ratio or ventilation quantity depending on the kind of a gas. In the case of a combustible gas such as monosilane, for instance, it is necessary to carry out ventilation by introducing air in an amount equal to 10 times the volume of the cylinder cabinet every minute. When such a large volume of air is used, it becomes difficult to detect a gas leakage even if it takes place.
On the other hand, it is known from experience that a gas leakage seldom takes place during the usual supply of a gas, rather it takes place, in many cases, upon the exchange of a gas container or just after the exchange. Namely, the gas leakage will take place where the closing of the valve of a gas container (which will be hereafter called “a container valve”) is unsatisfactory during the separation of a container valve and a pipe is carried out in order to exchange a gas container, or where the actual gas purge is started up in spite of the fact that the connection of the container valve and the pipe is unsatisfactory after the gas container exchange is completed. Also as to the place where a gas leakage occurs, it is known that such place is generally a specific given place, for example, a removable pipe joint between a gas container and a pipe, or a valve or a pressure reduction valve in a pipe.
Although the time when a gas leakage can occur and the location where it takes place are roughly understood, according to the gas leakage detecting apparatus of the prior art, a good detection result may not be obtained because the apparatus is constructed such that a gas leakage is detected by sampling air in an exhaust duct.
In consideration of this problem, it is an object of the present invention to provide a gas leakage detecting apparatus, by which the accuracy of detecting gas leaks can be improved.
SUMMARY OF THE INVENTION
In order to achieve the aforementioned objective, the present invention is characterized by a gas leakage detecting apparatus for detecting a gas leakage in a casing accommodating a gas container, which comprises: a gas sensor for detecting a leaked gas; a first air take-out pipe for taking out air from the inside of an exhaust duct provided in said casing and leading the same air to said gas sensor; a second air take-out pipe for taking out air at a given position in said casing and leading the same air to said gas sensor; a first shut-off valve and a second shut-off valve respectively provided in said first and second air take-out pipes so that air from said first and second air take-out pipes is selectively and controllably led to said gas sensor; and a control means for controlling the opening and closing operation of said first and second shut-off valves.
Although a gas leakage can be monitored, in normal operation, by sampling air in the exhaust duct from the first air take-out pipe as in the prior art, the present construction also enables one, on demand, to monitor a gas leakage locally by taking out air at an optional selected position, for example in the vicinity of a pipe joint in the casing of the second air take-out pipe.
It is preferred that a flexible portion be provided in the second air take-out pipe, whereby an end on the air take-in side of the pipe can be disposed at an optional selected position in said casing. If a to-be-connected member, to which the end of said second air take-out pipe on the air take-in side is detachably connected, is provided in said casing, and a connection detecting means for detecting whether said end on the air take-in side is connected with said to-be-connected member, the switching control of the first and second shut-off valves by the control device can be carried out on the basis of a detection result of the connection detecting means.
Furthermore, the apparatus may be designed such that the end of said second air take-out pipe on the air take-in side is fixed at a given position in said casing and said first and second shut-off valves are simply periodically opened and closed, alternately.
REFERENCES:
patent: 4294106 (1981-10-01), Gevaud et al.
patent: 5293771 (1994-03-01), Ridenour
patent: 5563335 (1996-10-01), Howard
patent: 6029503 (2000-02-01), Sumioki
patent: 64-84127 (1989-03-01), None
Burns Doane , Swecker, Mathis LLP
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Larkin Daniel S.
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