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consideration is given to the many factors which affect measurements, a whole set of books could be written about measuring techniques.
Briefly, because gases are compressible, effected by temperature, pressure and composition it is difficult to have a simple formula to use to calculate either leakage or flowrate through an orifice. Charle's and Boyle's laws give an idea of the problem but these laws are strictly limited to 'perfect' gases.
To take one example, the airflow through an orifice is effected by gas composition, turbulence (Reynold's number), pressure difference, the speed of gas flow, the orifice dimensions, the shape of the leading and trailing edge of the orifice etc...etc…! A typical practical example of these problems is the manufacture of gas jets for domestic appliances, to meet energy efficiency and safety requirements, the gas flow must be known and checked to be within 5% of the stated value. A single tiny burr on the inlet of the jet would cause the jet to be out of tolerance!
With our many decades of measuring experience in this area i.e. Working on the range of Solex air gauges and leak testers, designing and manufacturing the electronic versions of the Solex gauges (known as the QGS microflow air gauging instruments) and latterly designing our range of 'Mini-flow' instruments. We have become well acquainted with the many problems involved with making these measurements.
If measuring gas leak / flow is so difficult why not use liquid? The answer is simple, a tiny leak of liquid would result in a much larger leak of gas over a set time. Presented below are a few examples that we have encountered.
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