RU2313772C2 - Mode of control of insulation - Google Patents

Abstract

FIELD: the invention refers to the field of testing equipment and is directed on increasing sensitiveness of the control of insulation and accuracy in measuring of the size of leakage.

SUBSTANCE: the controlled article is placed in an insulated testing chamber from which air is removed. The cavity of the controlled article is filled with test substance (gas, vapor or liquid) under pressure of testing, after that the pumping of the chamber with the aid of a high-vacuum pump is stopped. In such condition the controlled article is hold during a definite period of time. Then the test substance (gas, vapor of liquid) accumulated in the chamber or in the volume of the article is pumped with the aid of the high-vacuum pump into a preliminary vacuum treated control chamber of a smaller volume then the volume of the test chamber. The leakage of the controlled article is estimated by measuring the reaction of a recording device (a leak detector) on content of test substance (gas, vapor of liquid) in the cavity of the control chamber.

EFFECT: increases sensitiveness of control of insulation.

2 dwg

Description

The invention relates to the field of testing products for leaks.

A known method of monitoring the tightness (patent of the Russian Federation No. 2187085, published on 08/10/2002), in which the product is placed in a sealed chamber, air is removed from the chamber, then the volume of the product is filled with a test substance and the chamber is kept for the accumulation of test substance. The leakage of the product is evaluated by measuring the content of the test substance in the chamber volume with a recording device (leak detector). In the case when the recording device has an atmospheric sensor capable of operating at atmospheric pressure, atmospheric air is let into the chamber before measurements.

When controlling the tightness of large-sized products, the method is inefficient, because requires too long a build-up of test substance. In addition, for products of complex spatial configuration, after the atmospheric air is poured into the chamber, it is not possible to ensure a uniform concentration of the test substance in the free volume of the chamber, as a result, large errors are made in the measurement, and in especially unfavorable cases, the presence of the test substance in the chamber may not show up.

Closest to the proposed invention is a method carried out using a device for monitoring tightness according to ed. testimonial. USSR No. 1395965, publ. 05/15/88, in which the product is placed in a sealed chamber, air is removed from the chamber, the product is filled with a test substance, kept for a certain time, then pumped through a cryochamber storage coil, on the cold walls of which the test substance condenses, and control is carried out after defrosting the coil.

The disadvantages of the method include the following:

- it is practically difficult to implement if hardly condensable gases are used as test substances: helium, argon, hydrogen;

- The use of cryogenic fluids is required.

The aim of the present invention is to increase the sensitivity of the tightness control due to the accumulation of test substances in a sealed chamber; improving the accuracy of measuring leaks.

The goal is achieved in the method of tightness control, in which the product is placed in a sealed chamber, the chamber cavity is evacuated, the product is filled with a test substance at a test pressure, disconnected from the pumping means and kept under these conditions for a certain time to accumulate a test penetrating through the leak in the chamber substances and determine the amount of leakage of the product by comparison with the response of the device to the reference concentration; Before measurements, the test substance accumulated in the chamber is pumped by the high-vacuum pump into the previously evacuated control chamber, the volume of which is less than the volume of the test chamber.

For each value of the volume of the control chamber, the necessary accumulation time of the test substance in the volume of the test chamber is determined by the ratio:

,

,

where V _to - the volume of the control chamber, m ³ ;

P _CR - the final discharge pressure of the high vacuum pump, Pa;

Q _Σ is the total leakage of the test chamber (leakage and gas flow of structural materials), m ³ Pa / s,

the value of the achievable sensitivity of the tightness control corresponds to:

,

,

where P _min - the minimum (threshold) partial pressure of the test substance (gas, steam), reliably recorded by the device, Pa.

The difference between the proposed method and similar methods is the compression of the accumulated test substance (gas, liquid vapor) in the volume of the control chamber when pumping the accumulated amount of it with a high vacuum pump, which is performed before the measurement of leakage by comparison with the reference concentration.

This method is applicable both to control the tightness of the entire product when it is placed in the test chamber, and to control the tightness of the product element when the accumulation of the test substance is carried out in the volume of the product itself.

Possible schemes for implementing the method are shown: in Fig. 1, with the accumulation of test substance in a sealed chamber, and in Fig. 2, with the accumulation of test substance in the volume of the product.

Prior to the test, the test substance is pumped and accumulated in the control chamber 6 from the reference leak 7 using a high-vacuum pump 5. Before that, the cavity of the control chamber is pumped out to high vacuum by a pump 4 through valve V4, then by a high-vacuum pump 5 through valves V3, V7 (valves V4-V6 are closed). For accumulation, open valve V8 of control leak 7 and valve V6 (valves V2-V5, V7 are closed) and in this state they withstand for a time t _n . Valves V8 and V6 are closed. Open valve V5 and let atmospheric air into the control chamber, providing a uniform concentration of the accumulated test substance in the volume of the control chamber. Open the cover of the control pipe and a sampling device of the recording device 8 take a sample of the analyzed gas medium. The reaction α _{et of the} recording device 8 to the content of the test substance in the control chamber is determined.

The sealed chamber 2 with the product 1 (figure 1) or the cavity of the product 1 (figure 2) is connected to the pumping system. The pumping system of the chamber (product) includes forvacuum 4 and high vacuum 5 pumps. As high-vacuum can be used, for example, steam jet, turbomolecular, molecular, twin-rotor pumps. From the chamber 2 (FIG. 1) or the cavity of the product 1 (FIG. 2), air is removed by the foreline pump 4, then it is pumped out to a residual pressure of less than 10 ^-4 mm Hg. high-vacuum pump 5. From the remote control 3 through the valve V1 into the cavity of the product 1 (figure 1) or the controlled element 2 of the product 1 (figure 2) serves a test substance at elevated pressure. Stop pumping by closing valve V2 and hold the chamber (product) to accumulate a test substance penetrating through leaks during t _n . In the process of exposure, air is removed from the cavity of the control chamber 6 by pump 4 through valve V4 (valves V3, V5-V7 are closed); pump it out with a high-vacuum pump 5 through valves V3, V7 (valves V4-V6 are closed). At the end of the accumulation of the test substance in the chamber 2 (Fig. 1), the cavities of the product 1 (Fig. 2) pump the accumulated amount by the high-vacuum pump 5 into the control chamber 6 through valves V2 and V6 (valves V3-V5, V7 are closed). By opening valve V5, atmospheric air is poured into the control chamber 6 (valves V3, V4, V6 are closed), ensuring a uniform concentration of the accumulated test substance in the volume of the control chamber. Open the cover of the control pipe and a sampling device of the recording device 8 take a sample of the analyzed gas medium. The reaction of α _{and the} recording device 8 to the content of the test substance in the control chamber is determined.

The leakage of the controlled product is estimated by the ratio

,

,

where Q _et - the magnitude of the flow of the test substance of the reference leak, m ³ PA / s;

α _and - the reaction of the recording device to the content in the control chamber of the test substance accumulated from the leakage of the product;

α _et - response of the recording device to the content in the control chamber of the test substance accumulated from the reference leak.

Experimental verification and testing of this method according to the scheme of figure 2 using sulfur hexafluoride (SF ₆ ) as a test gas showed the possibility of monitoring and measuring leakage with a flow value in the range (2 ÷ 10) · 10 ^-8 m ³ Pa / s. The maximum relative error in measuring flows of such a small value is ± (40 ÷ 50)%. The indicated characteristics correspond to those obtained during control by a mass spectrometric vacuum method using helium and argon as a test gas.

Verification of the method according to scheme 2 when using helium as a test gas can increase the sensitivity of control by at least an order of magnitude.

Claims (1)

The method of tightness control, namely, that the product is placed in a test chamber, the chamber cavity is sealed and evacuated, the test substance (gas, steam or liquid) is supplied with the test pressure into the cavity of the product, the chamber is disconnected from the pumping means and the test substance is accumulated in its volume for subsequent control of its concentration, characterized in that the accumulated test substance is pumped by a high vacuum pump into the previously evacuated control chamber before registration larger volume, for each value of the control chamber volume determined by the required time storage test substances in a volume ratio of the test chamber

where V _to - the volume of the control chamber, m ³ ; P _CR - the final discharge pressure of the high vacuum pump, Pa; Q _Σ is the total leakage of the test chamber (leakage and gas flow of structural materials), m ³ Pa / s, the value of the achievable sensitivity of the tightness control corresponds to

where P _min is the minimum (threshold) partial pressure of the test substance (gas, steam), reliably recorded by the device, Pa.

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