Helium leak detection

Imagine a room full of people. Now imagine you want to find the one(s) named Bill. If there was no way to easily identify the Bills, the process would become significantly laborious. However, if you called out and asked all those named Bill to please raise their hands, the task of identification becomes easy. The helium leak detector has the ability to isolate and count the helium atoms from a vacuum system full of many other atoms and molecules. In reality, the helium leak detector is nothing more than a customized mass spectrometer. The mass spectrometer was developed in the 1920s, but became a leak detection tool in the 1940s when the need for ultra-vacuum systems became critical on the Manhattan project.  

When helium leak detectors first became available, they were large and cumbersome and required highly trained technicians. They were also very expensive. Now, like most electronic equipment, they are smaller (relatively), easier to use (for some operations, they can be automated), less expensive, more reliable, more sensitive, and faster. As is typical of most things, helium leak detectors cannot have all the aforementioned attributes at once. However, it is possible to pick and choose which options are more important to you and select a detector that has features that are best suited to your needs. The usual tradeoff is sensitivity for speed. 

Although there are other leak detectors and leak detection techniques that rely on detection of a change in gas, none have enjoyed the success of the mass spectrometer tuned to helium. There are other types of tuned mass spectrometers that specifically look for oxygen or halogen, but they are not as common. Their opera- 

The use of helium as a probe (or tracer) gas in leak detection is not new. Before the mass spectrometer, it was used with thermocouple and/or Pirani gauges because of the greater thermal conductivity of helium than air. If you list all the attributes of a perfect probe gas, helium obviously does the job  

It should diffuse readily through minute leaks. 

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Where a vacuum is present inside the test specimen (p < 1 mbar), atmospheric pressure outside, and helium is used at the test gas, one refers to standard helium conditions. Standard helium conditions are always present during helium leak detection for a high vacuum system when the system is connected to a leak detector and is sprayed with helium (spray technique). If the specimen is evacuated solely by the leak detector, then one would say that the leak detector is operating in the direct-flow mode. If the specimen is itself a complete vacuum system with its own vacuum pump and if the leak detector is operated in parallel to the system s pumps, then one refers to partial-flow mode. One also refers to partial stream mode when a separate auxiliary pump is used parallel to the leak detector. 

Helium leak detection Helium 10" 10" 7 10 7.10" Vacuum, positive pressure Yes... 

An interesting article on the development of the helium leak detector can be found in the article History of Helium Leak Detection by Albert Nerken in the Journal of Vacuum Science, and Technology A, Volume 9, 3, pp. 2036-2038 (May/June 1991). 

This level of leak detection is not inexpensive A new mass spectrometer helium leak detector with the accompanying equipment can easily cost between 20,000 and 30,000. Purchasing used equipment can significantly reduce the initial costs, but one should not enter the level of helium leak detection because it seems like a good idea. On the other hand, if you need a helium leak detector, you cannot afford not to have one. 

There are four different approaches to helium leak detection. They are displayed in Table 7.17. A graphical representation of these techniques is shown in Fig. 7.59 through Fig. 7.61. 

General Tips and Tricks of Helium Leak Detection... 

Aside from permeability and absorbency complications, other universal concerns of helium leak detection are factors such as source operating pressure, spraying patterns (for tracer-probe technique), response time, clean-up time, and cold trap usage. Pump use and general helium leak detector maintenance operations are also fairly universal. 

Many methods have been used by industry to evaluate seal integrity. These range from very insensitive methods such as bubble testers to extremely sensitive methods such as helium leak detection. 

From the table one can see that only helium leak detection with a mass spectrometer leak detector allows a real quantitative statement of leakage rates compliant with the requirements of the ISO 9000 series of standards for quality management. Therefore this method and its variants will be described in more detail in the following. 

Helium Leak Detection in Industrial Rough Vacuum Applications 1183... 

Cumulative Helium Leak Detection (CHLD) is a variation on conventional leak detection that allows for gross and fine leak testing in the same pass and the potential for helium-leak detection at leak rates several orders of magnitude lower than with conventional leak-detection methods. 

Leak rates down to 10 Torr-liters/sec of nitrogen can be detected using helium leak detection methods. For accurate measurement the leak detector must be calibrated with a standard leak. 

Helium (leak detection) Gas (amu = 4) used for helium leak detection. ... 

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