JPS6093936A - Leak detector - Google Patents

Abstract

PURPOSE:To enhance the measuring accuracy of a leak amount, by receiving the vacuum system in a leak detector in a housing having a simple air-tight structure and flowing purge gas into said housing. CONSTITUTION:A pressure reducing valve 15 and a stop valve 19 are opened to introduce purge gas into a housing 13 from a purge gas bomb 14 and the introduction of purge gas is also succeeded during measurement. In the next step, a valve 11 is opened while a pump 12 and a diffusion pump 10 are operated to evacuate a vacuum system to a high vacuum degree and liquid nitrogen is further charged into a cold trap 7 and a valve 8 is opened to operate an analytical pipe 9. Subsequently, a body 1 to be tested is attached and a valve 3 is opened to roughly evacuate the body 1 to be tested and, thereafter, the valve 2 is closed while a valve 5 is opened to blow He gas (a) being a probe gas to the body 1 to be tested and He gas flowed into the vacuum system from a leak place is detected and quantitatively analyzed by the analytical pipe 9. As mentioned above, by filling the housing 13 with the purge gas during measurement, He-partial pressure in the housing 13 is lowered and the penetration of He into the housing 13 from the rubber gasket provided to each flange part of a leak detector is reduced to make it possible to enhance the measuring accuracy of a leak amount.

Description

[Detailed description of the invention] (b) Industrial application fields The present invention relates to a mass spectrometry type leak detector.

(b) Prior Art Normally, helium gas is used as a probe gas in a mass spectrometry type leak detector.

However, since the atmosphere also contains several ppm of helium,
Helium in the atmosphere enters the vacuum system of the leak detector due to permeation from the rubber gasket used as a sealing material in the leak detector or backflow from a diffusion pump. The signal due to atmospheric helium that has entered the vacuum system becomes the background of the original detection signal.

For this reason, conventional leak detectors have the disadvantage that they cannot detect the amount of leak with high precision due to the influence of helium in the atmosphere that enters the vacuum system.

In order to eliminate such drawbacks, a method of using a metal gasket as a sealing material has also been proposed and implemented. However, the use of metal gaskets presents a different problem in that it makes maintenance of the device significantly more difficult.

(C) Objective The object of the present invention is to provide a novel leak detector that can prevent atmospheric helium from entering the vacuum system of the leak detector.

(D) Structure The leak detector according to the present invention is characterized by comprising a simple airtight casing that houses the vacuum system of the leak detector, and means for flowing purge gas into the casing.

(E) Embodiment FIG. 1 is an explanatory diagram schematically showing the structure of an embodiment of a leak detector according to the present invention.

In the figure, 1 is a test object sealed with a rubber gasket. This test object 1 is connected to a roughing pump 3 via a roughing valve 2 .

7 and IO are a cold trap and a diffusion pump for high vacuum evacuation, and these are connected to the test object 1 via a test valve 5. 4 is a Virani vacuum gauge connected to the piping on the side of the test object 1, and 6 is a Penning vacuum gauge connected to the cold trap 7.

9 is an analysis tube connected to the cold trap 7 via the analysis tube valve 8; 12 is a forepump connected to the diffusion pump 10 via the forevalve 11.

Reference numeral 13 denotes a housing that houses the valves, pumps, analysis tubes, etc. that constitute the vacuum system of the leak detector described above. This housing 13 has a simple airtight structure.

In addition, a purge gas inlet 18 is provided at an appropriate location in the housing 13.
is provided. Purge gas is introduced into the housing 13 through this injection port 18 . As a purge gas,
For example, nitrogen gas, argon gas, etc. are used. The purge gas is supplied from a purge gas cylinder 14 provided outside the housing 13 via a pressure reducing valve 15 .

At a position facing the purge gas inlet 18, a purge gas exhaust duct 7 for discharging the purge gas is provided. Also,
Inside this duct 17, a pump exhaust duct 16 for the roughing pump 3 and fore pump 12 is installed. Thus, the exhaust purge gas and pump exhaust are exhausted through the containment valve 19.

Next, the operation of the above-described embodiment will be explained.

First, the pressure reducing valve 15 and the confinement valve 19 are opened, and the purge gas is introduced from the purge gas cylinder 14 into the housing 13. During measurement, this purge gas is constantly flowed. By filling the casing 13 with purge gas, the helium partial pressure within the casing is lowered, thereby reducing the permeation of helium from the rubber gasket of each flange portion of the leak detector.

On the other hand, in this embodiment, by integrating the purge gas exhaust duct 7 and the pump exhaust duct 16, the helium partial pressure at the pump exhaust port is lowered and the backflow of helium from the pump is reduced.

Then, the valve 11 is opened, the pump 12 and the diffusion pump 10 are operated to evacuate the vacuum system to a high vacuum, and liquid nitrogen is introduced into the cold trap 7. Valve 8 is opened and analysis tube 9 is activated. The test object 1 is attached, the valve 2 is opened, and the inside of the test object 1 is roughly evacuated, and then the valve 2 is closed and the valve 5 is opened. Helium, which is a probe gas, is blown onto the test object 1, and the helium flowing into the vacuum system from the leak point is detected and quantified by the analysis tube 9.

In the above embodiment, the test object 1, the purge gas cylinder 14, and the like were installed outside the housing 13.

However, the present invention is not limited to this, and these may be housed in the housing 13.

(F) Effect The leak detector according to the present invention houses the vacuum system of the leak detector in a simple airtight housing, and the purge gas flows into the housing, thereby preventing atmospheric helium from entering the vacuum system. can be reduced. Therefore, according to the present invention, it is possible to improve the accuracy of measuring the amount of leakage.

Further, according to the present invention, since rubber gaskets can be used for sealing parts of various parts of the vacuum system, maintenance of the apparatus can be performed more easily than when metal gaskets are used.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram schematically showing the configuration of an embodiment of a leak detector according to the present invention. 1... Test object, 13... Housing, 14... Purge gas cylinder, 17... Purge gas exhaust duct. Patent applicant Shimadzu Corporation Representative Patent attorney Takaharu Ohnishi

Claims (1)

[Claims] (1) A leak detector characterized by comprising a simple airtight casing that houses a vacuum system of the leak detector, and means for flowing purge gas into the casing.