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An integrated helium treatment plant from Witt Gasetechnik is improving the efficiency of a complex leak-testing procedure at Daikin, a manufacturer of air conditioning and heat pumps.

Depending on the type of application, various methods can be used to detect leaks that have been caused, for example, by material defects, improper processing or assembly – from simple water dip tests via differential pressure testing to leak tests with various test gases.

Helium is a commonly used inert gas as it offers several advantages.

It exists only to a low extent in ambient air and can be evidenced easily.

Helium is also non-toxic and odourless and does not react with other materials.

Its most important feature, however, is the small atomic radius that allows quick tests and detection of even the smallest leaks.

These features are utilised by Daikin.

One of the company’s largest production sites for cooling and heating units is located in Ostend, Belgium.

Leak tests have always been a key aspect of the Belgian production site’s quality assurance.

The operation of air conditioning equipment involves the use of fluorinated greenhouse gases that can have a significantly higher impact on the climate than CO2 when escaping into the atmosphere.

The systems manufactured by Daikin are therefore subject to particularly demanding leak-tightness requirements, which are required by law.

All units are controlled through a test-gas procedure in the context of a comprehensive test in order to avoid any and all leaks.

‘Each test sample is subject to the test gas and in the case of an undesired gas leakage, the component is considered to be defective,’ said Davy Van Rossem, Daikin Europe.

The test body is led into a test chamber for testing and connected to a test gas pipe.

The actual leak check is performed by a leak-testing unit, which registers escaping gas molecules up to the ppm (parts per million) size range.

During this local test procedure, an employee moves the test probe along the test unit in order to detect and localise eventual leaks.

R22 (difluorochloromethane) was previously used as the test gas.

This coolant gas has been banned across Europe due to its environmental impact and so Daikin has replaced R22 with helium.

In order to control the costs due to the expensive inert gas, the test method has been enhanced by a helium recovering unit: the precious gas is now almost recovered completely and reused.

The gas experts of Witten-based Witt Gasetechnik provided the technological core of this plant.

Christian Schmitz, product manager at Witt, explains: ‘The test plant with integrated helium recovery/treatment now features a closed-loop operation.

‘Witt gas mixers help to generate a mixture consisting of 20 per cent helium and 80 per cent nitrogen, which is densified by compressors and led with a pressure of up to 42 bar into the component to be tested.

‘Subsequent to the test, the used gas is captured, cleaned and led into a balloon, which serves as a buffer storage.

‘We then use our analysis system to measure the remaining helium content in the balloon and add helium as required.

‘Once the optimal mixture has been re-established, the gas is fed back into the test circuit – fully automatically,’ he added.

The mixing ratio must remain constant during all phases of the test procedure in order to make a final assessment concerning eventual leaks.

State-of-the-art sensor systems are used to ensure that this requirement is met.

The helium percentage is determined by using a measuring cell operating according to the thermal conductivity principle.

A paramagnetic measuring cell is used for the oxygen analysis.

The process accuracy and the interaction of the components are the main technological challenges.

For the Daikin project, Witt has combined its individual solutions for analysing, mixing and dosing gases in a complex overall solution that features high precision and reliability.

A total of 19 test lines for various device sizes have been integrated into the test plant.

Nearly 2,000 units are leak tested daily and delivered by the Daikin Europe site in Belgium.

Each unit is tested twice, which means about 4,000 tests a day.

Witt Gasetechnik

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