JPH11211604A - Helium leak detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide detector for detecting leakage of helium from an objective container stably with high sensitivity utilizing counter flow of a turbo molecular pump. SOLUTION: An analyzing chamber 3 is disposed on the suction port 6a side of a turbo molecular pump section 4 having a delivery port 6b coupled with a container 2 to be inspected and a screw seal part 5 is disposed on the delivery port 6b. The screw seal part 5 is formed as an auxiliary pump exhibiting a small conductance to the turbo molecular pump section 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a helium leak detector which is most suitable for inspecting a container or the like which requires airtightness for leakage.

[0002]

2. Description of the Related Art Helium leak detectors are used for inspection of the hermeticity of containers in nuclear facilities and the like in which a very small amount of leakage is not allowed.

FIG. 8 shows an exhaust system diagram of a typical counter flow type helium leak detector.

That is, the container V to be inspected is placed in a helium gas atmosphere, and a turbo molecular pump a and an auxiliary vacuum are used to check whether the surrounding helium gas is leaking and entering the container V to be inspected. The pump b and the analysis chamber c are connected to form a helium leak detector.

[0005] The turbo-molecular pump a exhausts gas from the analysis chamber c toward the auxiliary vacuum pump b. As a characteristic of the turbo-molecular pump, there is a counter flow which flows in a direction opposite to the exhaust direction. If helium gas has leaked into the container V to be inspected, the leaked gas enters the analysis chamber c along this counter flow. So this analysis room c
If helium is detected in the container, it is known that there is a leakage point in the container V to be inspected.

In order to further increase the detection sensitivity of this conventional helium leak detector, a flow control valve is interposed between the exhaust side of the turbo-molecular pump a and the auxiliary vacuum pump b to provide a back pressure side of the turbo-molecular pump a. There is known an example in which a very small conductance is provided to the horn. This is to increase the flow rate of the counter flow by making the exhaust speed of the auxiliary vacuum pump b extremely small.

In general, an oil rotary vacuum pump is used as the auxiliary vacuum pump b.

[0008]

When the conductance on the back pressure side of the turbo molecular pump a is to be obtained by the throttle action of the flow control valve, there is a fact that the conductance of the throttle is inversely proportional to the square root of the molecular weight of the flowing gas. .

When a mixed gas of air and helium passes through the flow control valve, the conductance of helium having a molecular weight of 4 becomes approximately 2.7 times the conductance of air having a molecular weight of 29, and the auxiliary vacuum passes through the flow control valve. Since the proportion of helium gas flowing to the pump b increases, the proportion of air, which is a noise source, in the gas sent to the analysis chamber c on the counter flow increases, which lowers the sensitivity of the helium leak detector. .

When the conductance is to be obtained by the throttle function of the flow control valve, it is necessary to keep the throttle setting value of the flow control valve unchanged in order to keep the conductance constant. However, there is a problem that it is very difficult to finely adjust the aperture value and keep it constant.

Further, the oil rotary vacuum pump generally used as the auxiliary vacuum pump has a structure in which a part of the oil is introduced into the cylinder, so that the helium gas in the exhaust gas dissolves in the oil, When the dissolved helium gas gradually or suddenly departs from the oil, the background pressure in the analysis chamber c fluctuates, and the measured value of the detector becomes unstable.

An object of the present invention is to solve these problems and to provide a helium leak detector capable of measuring helium leak with high sensitivity and stability.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a helium leak detector for inspecting leakage of a container or the like using a counter flow of a turbo molecular pump. An analysis chamber is installed on the mouth side, the outlet side of the turbo-molecular pump is connected to the container to be inspected, and a screw seal is installed on the outlet side, and the screw seal has a small conductance with respect to the turbo-molecular pump. It is characterized by being formed in an auxiliary pump having.

[0014]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIGS.

In the exhaust system diagram of the first embodiment shown in FIG. 1, reference numeral 1 denotes a helium leak detector, and 2 denotes a container to be inspected.

The helium leak detector 1 has an analysis chamber 3,
It comprises a turbo molecular pump section 4, a screw seal section 5, and the like.

Since helium is used as a probe gas for inspecting the container 2 to be inspected for leakage, a helium detector (not shown) is installed in the analysis chamber 3.

The analysis chamber 3 is connected to a turbo molecular pump section 4.
And the outlet 6b of the turbo molecular pump unit 4 is connected to the container 2 to be inspected.

The turbo-molecular pump section 4 and the screw seal section 5 are integrally combined to form a pump assembly 6. .

FIG. 2 is a longitudinal sectional view of the pump assembly 6.

That is, the turbo molecular pump section 4 comprises a number of moving blades 4a and a number of stationary blades 4b, etc.
Is fitted and fixed to a rotating shaft 4d by a rotating body which is attached to the periphery thereof. Further, a thread groove 5a is installed on the rotating shaft 4d following the rotating body 4c, and the screw sealing portion is formed together with a discharge port 6c described later. 5 are formed.

The screw shaft 5 is provided on the rotating shaft 4d.
Subsequently, a journal bearing 7 using a herringbone dynamic pressure type gas bearing and a thrust bearing 8 using a spiral groove dynamic pressure type gas bearing are sequentially installed.

Reference numerals 6a and 6b denote an inlet and an outlet of the turbo molecular pump section 4, respectively. The inlet 6a is connected to the analysis chamber 3, and the outlet 6b is connected to the container 2 to be inspected. I have.

Reference numeral 6c denotes a discharge port, which discharges a small amount of exhaust gas from the screw seal portion 5, and discharges a part of the atmosphere supplied to the gas bearing from the air supply port 6d through the discharge port 6c.

The screw seal portion 5 also serves to prevent the air flowing into the gas bearing from entering the housing 6h.

Reference numeral 6e denotes a cylindrical body which forms the screw seal portion 5 and the journal bearing 7 on the bush side.

Reference numerals 6f and 6g denote thrust receiving surfaces before and after the thrust bearing 8, respectively.

Reference numeral 9 denotes a motor, and 10 denotes a fixing nut.

FIG. 3 shows an example of the structure of the shaft portion of the herringbone dynamic pressure type gas bearing constituting the journal bearing 7 and an example of the structure of the spiral groove dynamic pressure type gas bearing constituting the thrust bearing 8. Is shown in FIG.

That is, in FIG. 3, reference numeral 7a denotes a large number of grooves formed in a C-shape in the rotation direction. In FIG. 4, reference numeral 8a denotes a number of spiral grooves formed on the upper surface of the thrust bearing 8, and a number of similar spiral grooves are also formed on the lower surface of the thrust bearing 8.

The turbo molecular pump unit 4 sets the compression ratio with respect to helium gas in the range of 10 to 1000 and sets the pumping speed of the screw seal unit 5 to 0.001.
To 0.1 L / s, the screw seal portion 5
Was formed to be an auxiliary vacuum pump having sufficiently small conductance with respect to the turbo molecular pump section 4.

Next, the operation and effects of the first embodiment will be described.

In the helium leak detector 1 shown in the drainage system diagram of FIG. 1, when the pump assembly 6 having the structure in which the turbo molecular pump section 4 and the screw seal section 5 are integrated is operated, the turbo molecular pump section 4, the inside of the analysis chamber 3 is evacuated by the evacuation action, and the exhaust port 6b of the turbo-molecular pump section 4 becomes negative pressure by the evacuation action of the screw seal part 5 as an auxiliary pump. The pressure in the connected container 2 also becomes a negative pressure.

Therefore, when the container 2 to be inspected is placed in a helium gas atmosphere, if there is a leak portion in the container 2 to be inspected, the helium gas entering therefrom is discharged to the discharge port side of the turbo molecular pump unit 4. And a part of it reaches the analysis chamber 3 by the counter flow of the turbo molecular pump section 4.
And the container 2 to be inspected is detected by the helium detector.
Is detected with high accuracy.

The reason is explained by the following logical expression.

Q: Amount of gas released from the inner wall of the container 2 to be inspected
[P a · L / s] q: the amount of gas released from the inner wall of the analysis chamber 3 and
Leak amount [P a · L / s] M: leak amount to the container 2 to be inspected [Pa · L / s] C: between the container 2 to be inspected and the helium leak detector 1
Pipe conductance [L / s] S: Pumping speed [L / s] of turbo molecular pump unit 4 S ': Pumping speed [L / s] of screw seal unit 5 R: Compression ratio of turbo molecular pump unit 4 ₁: Pressure [Pa] P in the container 2 to be inspected_Two: Back pressure [Pa] P of turbo molecular pump unit 4_Three: Pressure [Pa] in the analysis chamber 3

The relationship between each parameter of S, S ', R, C, Q, and q and each pressure P ₁ , P ₂ , P ₃ is governed by Equation 1.

[0038]

(Equation 1)

The solution of this simultaneous linear equation is given by Equations 2 to 4.

[0040]

(Equation 2)

(Equation 3)

(Equation 4)

Here, since the leak amount M is composed of helium and air, whereas helium is not contained in Q and q, the first term on the right-hand side of the equation (4) should be more dominant than the second term. of the pressure P ₃ in the analysis chamber 3, it can be seen that to improve the partial pressure of helium gas. For this, S is large,
It is better that RS 'is smaller.

However, in order to increase the counter flow effect of the turbo-molecular pump, the compression ratio R
Is desirably increased, so that the pumping speed S ′ of the screw seal portion 5 needs to be a very small value.

Thus, in the helium leak detector 1 of the present invention, the compression ratio of the turbo molecular pump section 4 is increased, and the exhaust speed of the screw seal section 5 as an auxiliary pump is extremely reduced. The portion 4 was formed to have a small conductance.

Unlike a throttle mechanism such as a flow control valve, a screw seal stably generates a minute pumping speed and generates a substantially constant pumping speed irrespective of the type and molecular weight of gas. It has the feature to make it.

With respect to the general values of Q, q, and M shown in Table 1 of FIG. 5, the calculation results of Equations 2 and 3 for the exhaust system of the conventional general counter-flow helium leak detector are shown in FIG. In addition, Table 2 in FIG. 5 shows the calculation results for the exhaust system of the helium leak detector of the present embodiment.

The partial pressure of helium of P _{3 in} the exhaust system of the present embodiment is nearly 100 times that of the conventional exhaust system, and the residual pressure in the container becomes a noise when detecting leakage. Since the ratio of the partial pressure of water, which is the main component of air and the gas released from the inner wall of the container, to the partial pressure of helium is much smaller than in the past, it can be seen that high sensitivity can be obtained by the leak detection.

In the present embodiment, a dynamic pressure type gas bearing is adopted for the turbo molecular pump section 4 and an oil rotary vacuum pump such as a conventional auxiliary vacuum pump is not used. Since no liquid such as oil is used, there is no problem that the background pressure of the analysis chamber 3 fluctuates.

Further, in the present embodiment, the turbo molecular pump section 4 and the screw seal section 5 are integrated, and the screw seal section 5 is connected to the housing 6h from the gas bearing.
Since it was formed so as to also serve to prevent gas from entering into the inside, the size of the apparatus including the pump assembly 6 could be reduced.

In this embodiment, the turbo molecular pump section 4 employs a dynamic pressure type gas bearing, but it may be a ball bearing or a magnetic bearing type.

A second embodiment of the present invention will be described with reference to the exhaust system diagram of FIG.

In this embodiment, a turbo molecular pump 11 is provided between the helium leak detector 1 and the container 2 to be inspected.
Is different from the first embodiment.

Since the outlet side of the turbo-molecular pump 11 is connected between the turbo-molecular pump section 4 and the screw seal section 5 as described above, the exhaust of the container 2 to be inspected is performed by the operation of the turbo-molecular pump 11. The helium leak detector 1 can improve the responsiveness of the helium leak detector 1 as compared with the first embodiment, since the minute exhaust action by the screw seal portion 5 can be supplemented.

A third embodiment of the present invention will be described with reference to an exhaust system diagram of FIG.

In this embodiment, a vacuum pump 12 for roughing the container 2 to be inspected is additionally provided in the second embodiment.

The vacuum pump 12 for roughing may be a turbo molecular pump or an oil rotary vacuum pump, and the container 2 to be inspected is evacuated in advance by the vacuum pump 12 so that the helium leak detector 1 rises. Can be hastened.

[0056]

As described above, according to the present invention, it is possible to stably measure helium leakage with high sensitivity and to provide a small and compact helium leak detector.

[Brief description of the drawings]

FIG. 1 is an exhaust system diagram of a first embodiment.

FIG. 2 is a vertical sectional view of the pump assembly.

FIG. 3 is an explanatory diagram of a shape of a main part of a herringbone dynamic pressure type gas bearing.

FIG. 4 is an explanatory view of a shape of a main part of a spiral groove dynamic pressure type gas bearing.

FIG. 5 is a table comparing the results of performance calculations of the helium leak detector.

FIG. 6 is an exhaust system diagram of a second embodiment.

FIG. 7 is an exhaust system diagram of a third embodiment.

FIG. 8 is an exhaust system diagram of a conventional helium leak detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Helium leak detector 2 Container to be inspected 3 Analysis room 4, 11 Turbo molecular pump 4c Rotating body 4d Rotary shaft 5 Screw seal 6a Inlet 6b Outlet 6h Housing 7 Journal bearing 8 Thrust bearing 12 Vacuum pump for roughing

Claims (5)

[Claims] In a helium leak detector of a type in which a leak of a container or the like is inspected by utilizing a counter flow of a turbo-molecular pump, an analysis chamber is provided on a suction port side of the turbo-molecular pump, and the turbo-molecular pump is discharged. Connect the outlet side to the container to be inspected and install a screw seal on the outlet side,
A helium leak detector wherein the screw seal is formed in an auxiliary pump having a small conductance with respect to the turbo molecular pump. 2. The turbo-molecular pump has a rotating body that rotates at a high speed in a housing, forms the screw seal on a rotating shaft of the rotating body, and integrates the turbo-molecular pump and the screw seal into the housing. The helium leak detector according to claim 1, wherein the helium leak detector is built in the helium leak detector. 3. The compression ratio of the turbo molecular pump to helium gas is set in the range of 10 to 1000, and the pumping speed of the screw seal is 0.001 to 0.1 L.
The helium leak detector according to claim 1, wherein the helium leak detector is set in a range of / s. 4. The helium leak detector according to claim 1, wherein a second turbo molecular pump is interposed between the discharge side of the turbo molecular pump and the container to be inspected. 5. The helium leak detector according to claim 4, wherein a vacuum pump for rough evacuation is provided in the container to be inspected.