Leak detectors

The helium leak detector is a common laboratory device for locating minute leaks in vacuum systems and other gas-tight devices. It is attached to the vacuum system under test a helium stream is played on the suspected leak and any leakage gas is passed into a mass spectrometer focused for the helium-4 peak. The lack of nearby mass peaks simplifies the spectrometer design the low atmospheric background of helium yields high sensitivity helium s inertness ensures safety and its high diffusivity and low adsorption make for fast response. 

Valves are mounted so that the plug of the valve is flush with the tank to avoid a pocket of unpasteurized milk, and a leak detector valve permits drainage of the milk trapped in the plug of the valve. Ad. covers, piping, and tubing must drain away from the pasteurizer. 

Soundness of safety shut-off valves in the closed position for both forward and reverse flow. Note that this should be done with the valve in situ and without dismantling it, by means of a bubble leak detector, etc. The valve should not be dismantled to check for swarf on the seat, etc. 

The period between such tests will depend on the maintenance schedule for the plant, which should also include the in-situ soundness testing of non-return valves and safety shut-off valves by bubble leak detectors, etc. 

Two types of ultrasonic systems are available that can be used for predictive maintenance structural and airborne. Both provide fast, accurate diagnosis of abnormal operation and leaks. Airborne ultrasonic detectors can be used in either a scanning or contact mode. As scanners, they are most often used to detect gas pressure leaks. Because these instruments are sensitive only to ultrasound, they are not limited to specific gases as are most other gas leak detectors. In addition, they are often used to locate various forms of vacuum leaks. 

Fig. 1.34. Scheme of a leak detector analysis cell (courtesy of Alcatel). 

Open the thermal switch by pumping away the helium gas from the IVC and start the DR unit. Sometimes one goes on pumping the IVC while temperature decreases. In this case, since also the cold surfaces of DR act as cryogenic pumps, a flux meter (usually present in a leak detector) tells when pumping must be interrupted (at about 1 K). Otherwise, it is safe to close pumping at 4K. 

Chamber with a leak 2, helium leak detector 3, pressure bottle with helium 4, vacuum pumpsystem, evacuating the chamber 5, helium spray pistol (Fig. 3 from [2.26]). 

Object to be tested 2, helium leak detector L, slit with a fixed conductivity (Fig. 10 from [2.27]). 

Fig. 2.36. Helium leak detector in operation at an industrial vacuum plant. The leak detector stands behind the hand rail, the flange is sprayed with He, the mobile indicator is held in the left hand (photograph Balzers und Leybold Holding AG, D-63450 Hanau).

Are leak detectors with local and remote audible and visible alarms present, operable, and tested ... 

Leak Testing Location of through wall defects and flaws while under pressure or vacuum. Various fluids and gases are used for pressure testing several types of leak detectors are used to locate a leak. 

Improved slide valves can lead to a more reliable FCC operation. Better actuators provide a more rapid response to process changes and can prevent unnecessary unit trips. Changing the internals to allow the valves to operate in the desired 35-65% open range gives better control and reduces wear. Expansion joints can be updated with better metallurgy and dual plys with leak detectors can be used. This can help avoid a shutdown and improve both safety and reliability. 

Switch to modern, two-ply expansion joints wifli leak detectors... 

Adjustment or tuning refers to the correct setting of an instrument. For example, setting 0 and 100 % in THERMOVACs or setting the mass spectrometer to mass 4 in the helium leak detector. 

Partial pressure analysis using a mass spectrometer or the pressure rise method may be used to differentiate between these two causes. Since the pressure rise method will only prove the presence of a leak without Indicating Its location In the apparatus. It Is advisable to use a helium leak detector with which leaks can, in general, also be located much more quickly. 

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. 

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