A predetermined test pressure is maintained within the test volume using a precision pressure regulator. For makeup flow, after the test gas has stabilized within the test volume, a maintenance flow through the system compensates for any leakage in the test volume. This maintenance flow is equal tthe amount of leakage in the test volume, and is measurement and displayed by the precision mass flowmeters.
In pressure decay applications, after the test gas has stabilized, the instrument is isolated from the test volume except for the pressure sensor. This sensor measures the drop in pressure caused by a leak within the test volume. This pressure loss, over time, is directly related tthe leakage rate.
Thermal mass flowmeters allow for direct reading without requiring corrections for temperature or pressure. These flowmeters provide high accuracy and responsiveness and can withstand pressurization and flow fluctuations without damage.