James Walton
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Quality Control has a very high value. The value comes from the security it provides. Air and Liquid tightness can be of critical importance, also on a small scale. It is our mission to support the development of tools that can help achieve this goal. Leaks can lead to unstable process conditions which in turn can create potentially dangerous results. An example is the Bhopal disaster : a gas leak incident in India which is considered as the world’s worst industrial disaster. Over 500,000 people were exposed to methyl isocyanate gas and other chemicals.

There are three major solutions that we have provided to demonstrate leak integrity:

  • Valve seat leak testing
  • Fabric permeability testing
  • Ventilation and Air conditioning systems (HVAC)

Each of the challenges has different demands and requires an independent approach.

Two of these solutions required a flow pressure combination and one was a Coriolis solution. The valve seat leak test required a Coriolis sensor to meet the specific demands of that industry. Both the fabric and ventilation systems required a Thermal Mass Flow meter and Pressure instrument and that is what we are talking about this week.

Fabric permeability testing

The fabric test was completed by using a closed loop flow-pressure control solution. A chamber with an outlet, Digital Electronic Pressure Meter (DEPM) to control the internal pressure and an inlet, Mass Flow Controller (MFC) to control the inlet flow was built with a custom made fabric clamp on top of the chamber for the fabric.

This system allows the end user to clamp in a chosen fabric sample, always a consistent size, give set-point to the pressure meter, which via a closed loop control cable then controls the valve on the mass flow controller to allow the addition of air into the chamber until the pressure set-point is reached and then maintain it. Once reached the flow controller records the flow of AiR required to maintain the set-point giving a value to the permeability of the fabric. This process provides data acquisition for the test.

Ventilation and air conditioning system

The ventilation leak test system requires a more industrial approach. Also, with larger volumes to fill and potentially several devices under test (DUT) the system is controlled by a Digital Electronic Pressure Controller (DEPC). A Mass Flow Meter (MFM) is used in series to meter the flow of AiR required to maintain the set pressure. With an MFM and DEPC in-series you can set a pressure on the DUT via the DEPC and fill with AiR, the DEPC then controls the pressure while the MFM records the amount of AiR required to maintain the pre-determined pressure. This will then give a reading on the leakage rate of the DUT. Image description

There are a few key factors to making sure that you get repeatable and consistent test data:

Firstly, if the test volume would require a long fill time, or secondly, a small leak rate might be measured then a safe by-pass would be required to achieve a quick fill and stabilisation time.

The third and most important parameter that can affect the result of the test is temperature. The gas and components must be allowed to equalise before testing begins, for example a 2 Deg C shift in temperature can result in a 0.7% change in volume measured due to gas expansion. Any leaks smaller than this volume would not be measured and the integrity and repeatability of the test would be under question.

To help counter some of the issues discussed we have developed a new flow controller that will provide your process with cutting edge performance, click here for more information.

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