Measuring and testing – With fluid pressure – Leakage
Patent
1994-06-01
1996-07-23
Williams, Hezron E.
Measuring and testing
With fluid pressure
Leakage
73 40, G01M 320, B01D 5700
Patent
active
055378579
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a leak indicator for vacuum systems comprising a chamber which is evacuated while the system is in operation plus a vacuum pump used to evacuate the chamber whereby the leak indicator has a test-gas detector in the form of a mass spectrometer plus a high vacuum pump to produce the vacuum necessary for operation of the mass spectrometer.
2. Discussion of the Related Art
Before operation, after maintenance or repair work and also after other interruptions of operation, vacuum systems must be tested for the presence of leaks so as to ensure optimum operating conditions of the vacuum system which are not adversely influenced by flows of leaking gas.
From DE-OS 33 16 765 a method and device is known for the detection of leaks on turbine casings. A low pressure is maintained in the turbine casings with the aid of vacuum pumps. For the purpose of leak detection all parts of the turbine casing where a leak is suspected are sprayed from the outside with a test gas, preferably helium. The exhaust gas of the vacuum pumps is monitored with the aid of a sniffer leak indicator so that the presence of any leaks can be determined. Leak detection of this kind is relatively insensitive.
Moreover, the leak detection arrangement for this task is fairly large and heavy, because such an arrangement must include a complete high vacuum system with a heavy backing pump.
OBJECTS AND SUMMARY OF THE INVENTION
It is the object of the present invention to increase detection sensitivity of the leak detection process on vacuum systems while at the same time reducing the technical complexity of the arrangement.
This object is accomplished according to the present invention by leak indicator as outlined above by making the chamber of the vacuum system connectable to the inlet and/or exhaust side of the high vacuum pump in the leak indicator via a constriction. The introduction of a suitably rated constriction ensures that the pressure in the mass spectrometer remains sufficiently low. Due to the direct connection between the chamber of the vacuum system and the leak indicator, the flow paths for the test gas between a possibly present leak and the mass spectrometer detector are considerably shorter compared to the state-of-the-art thereby offering improved sensitivity and a reduction of complexity.
A particularly advantageous further development is, that the constriction is made to act as a control valve. With the aid of this control valve the gas flowing into the mass spectrometer detector can be throttled in such a way, that the pressure in the mass spectrometer can be maintained at a constant level, irrespectively of the process pressure in the system and this preferably at an optimum high total pressure of approximately 10.sup.-4 mbar. In such a mode of operation the leak indicator will operate as a concentration measuring instrument for the test gas, so that the interfering gas concentration in the process is indicated to the persons responsible for running the process. Concentration changes are measured correctly and independently of any total pressure variations during the process, even if the leak rate itself remains constant (the leak rate is only the cause for the quantity of the gas concentration which interferes with the process).
A further advantageous measure is, to employ a pump system in the leak indicator which consists of a high vacuum pump and a further pumping stage, so that on the pressure side of the pump system a pressure can be produced which is of the same order of magnitude compared to the operating pressure within the chamber of the vacuum system, 40 mbar, for example. With such a pump system it is possible to connect the exhaust of the pump system to the chamber of the vacuum system, so that it will no longer be required to equip the leak indicator itself with a backing pump. Thus the leak indicator is light-weight and especially handy which is of great importance especially during leak detection on large fixed installations.
BRIE
REFERENCES:
patent: 4735084 (1988-04-01), Fruzzetti
patent: 4773256 (1988-09-01), Saulgeot
patent: 4776207 (1988-10-01), Holme
patent: 4779449 (1988-10-01), Bley et al.
patent: 5049168 (1991-09-01), Danielson
patent: 5131263 (1992-07-01), Handke et al.
patent: 5168747 (1992-12-01), Weaver et al.
patent: 5297422 (1994-03-01), Baret
patent: 5317900 (1994-06-01), Bergquist
Leybold AG
Wiggins J. David
Williams Hezron E.
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