Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
1998-04-15
2001-03-06
Larkin, Daniel S. (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S049300
Reexamination Certificate
active
06196056
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to apparatus to detect leaks within fluid or gas containing systems. More particularly, the invention relates to a system for testing the integrity of gas-seals constructed within fluid containing apparatus or gas-containing sub-systems within test objects which includes injecting a test gas into the test object, detecting a presence of test gas at or near the object on assumption that same passed through a break in a gas-seal sealing the object/sub-system, and recycling the test gas used.
2. Description of the Related Art
In manufacturing and industry, various components and apparatus are known (referred to herein as “equipment” or “test objects”) manufactured as, or to include gas- or fluid-filled subsystems for their normal operation. Of course the seals required by same mentioned components and apparatus are tested before the test object is put in commerce. The accuracy of the testing, i.e., the ability to identify and separate test objects, the seals of which are required intact normal operation is paramount to maintaining consistent quality control standards, and therefore quality of the apparatus known commercially.
The need for accurate and efficient methods for testing gas- or fluid-filled apparatus has facilitated development of dedicated test apparatus and methods to verify the integrity of seals in apparatus requiring same. Conventional apparatus and methods enable a manufacturer or OEM to verify the integrity seals within, for example, refrigeration fluid sub-systems under certain test conditions. Prior art seal-testing apparatus use a test gas containing some type of trace molecule or entity used to conduct integrity studies of seals or sealed subsystems within test objects. The gas is injected into the subsystem, and the object is “sniffed” for leaked portions of the test gas.
Conventional gas-seal test equipment attempts to verify the presence of the test gas, usually using spectroscopic equipment, such as an electron capture detector.
For example, U.S. Pat. Nos. 5,317,159, 5,293,130, 3,714,421, 3,892,968, disclose various gas-seal integrity testing apparatus which utilize mass spectrometers. For example, a gas leak detection system
1
of the prior art is shown in
FIG. 1
which utilizes pressurized test gas and a mass spectrometer in a method of use known “pressure/accumulation testing” to verify the integrity of seals which seal a gas- or fluid-containing sub-system
2
a
within a test object
2
.
The system
1
includes a mass spectrometer
8
connected to a “sniffer” probe
4
. The sniffer probe
4
is constructed in fixed fluid communication with mass spectrometer
8
via a flexible hose or tube
10
. The spectrometer includes an ionization chamber to ionize particular gas or gases present in the ionizing chamber. During testing, the subsystem is charged with a helium-containing test gas. Hence, an amount of the test gas injected into the test object must be sufficient to generate a pressure within the test object
2
significantly greater than atmospheric pressure, or one (1) atmosphere (Atm.), to ensure that a sufficient amount of test gas leaks into the atmosphere around the object to be clearly identified by the system
1
.
The test object
2
is inserted into testing chamber
6
to which the sniffer probe
4
is attached. Any break or fault in the seal of subsystem
2
a
provides a path for pressurized test gas (containing the helium) to escape into the testing chamber. The chamber
6
is “sniffed” for helium or traces of helium in a flow of gas drawn into the sniffer from the atmosphere surrounding the test object (inlet
4
a
) of the sniffer probe. That is, gases near the test object are sucked into the sniffer probe. The sniffed gases pass through hose
10
into mass spectrometer
8
. That is, detector
8
verifies the presence of (and/or quantity of) helium in the gas collected, typically in parts per million. Detection of helium is indicative of a leak in the subsystem of the test object being tested.
Pressure/accumulation testing so described is useful for verifying the integrity of seals sealing gas subsystems within large test objects, such as tanks, particularly those including gas-filled sealed compartments of which are not easily evacuated, but are built to withstand stresses generated by large differential pressures, or a leak rate specifications which are strenuous in view of the art. The reader must note that the accuracy of such testing is limited where the sniffer gas sample contains gas leaked from the subsystem. That is, because the “sniffer probe” takes in surrounding air and its adulterants, it cannot be assumed that intaken air has tracer gas even though same indeed leaked from the test object
1
. That is, non-metered volumes of atmospheric gases present at or near the test object during testing could also lead to significantly diluted test gas concentrations, and therefore, accuracy of the test.
Vacuum testing is also known, such as vacuum detection system
21
of FIG.
2
. Vacuum detection system
21
is shown in the figure to include a helium detector or mass spectrometer
8
connected in fluid communication with a vacuum pumping system
22
by tube or gas conduit
20
. Conduit
20
also connects detector
8
and system
22
to subsystem
2
A within test object
2
. The vacuum pumping system
22
allows the helium detector
8
to operate under high vacuum pressure to evacuate the sealed fluid subsystem
2
A during testing. The test requires that a fine spray of helium (which may be contained in a conventional gas tank
28
) is directed over the outside of test object
2
using a helium sprayer
24
. If a flaw in the seal exists, helium will pass into the subsystem through the flaw induced by the pressure differential. Tube
20
transports the input gas to mass spectrometer
8
, where, if helium is detected, a leak is assumed.
An obvious drawback exists in that any gases drawn into the system may contain relatively insignificant or undetectable amounts of helium tracer gas. Hence, detection of helium leaked by the test object will be available in detectable amounts in the sucked-in gases only if the test object
2
is “sufficiently” sprayed, and/or the flaw or leak is “sufficiently” large. So vacuum-testing technology works only as long as helium present in the gas sample is not overly diluted to amounts outside the effective detection ability of the vacuum-based system. A not so obvious drawback to conventional technologies is that the high vacuum pressure utilized in the vacuum test requires mechanical apparatus of substantial size (and maintenance) at the place of testing, which also increases system construction costs.
Shortcomings in conventional vacuum testing, and/or accumulation-pressure testing technology led to yet another conventional leak detection system
31
which utilizes a combination of the pressure and vacuum testing technologies (FIG.
3
). System
31
includes a mass spectrometer
8
and a vacuum chamber
34
attached to the spectrometer via gas conduit. Conduit
20
is also connected at its other end to a vacuum pumping system
22
. To use system
31
, the user must first use a gas injection means (not shown in the figure) to inject a test gas into the closed space or sealed gas-filled subsystem within test object
30
which is to be tested. Helium is injected into object
30
to generate an internal gas pressure greater than one atmosphere. The helium-pressurized test object
30
is placed within test chamber
34
. The test chamber
34
is evacuated to less than atmospheric pressure via vacuum pumping station
22
. This process results in a reduction of helium concentration contained within air filling the chamber to a helium concentration significantly below that normally found in air. The accuracy of the leak detection is improved in kind.
Hence, if a flaw allowing gas leakage from the sealed subsystem of the test object exists, the pressurized helium will leak from same to be detected as the gas from the chamber
34
Ewing Fritz
Linzer Stuart
Larkin Daniel S.
Scully Scott Murphy & Presser
Vacuum Instrument Corp.
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