Appnote: Even faster (and simpler) leak checking

Even faster (and simpler) leak checking

Fast and accurate leak checking can be a complicated process requiring a rather complex setup, often involving several flow and pressure controllers to accurately detect even small leaks. While pressure decay tests are often suitable, Alicat previously recommended a method which involved using a mass flow meter and remote-sensing pressure controller in parallel, plumbed to control pressure into the device under test (DUT) and monitor any resulting flows out.

However, with the introduction of the Whisper-Series low pressure drop mass flow meters and controllers, Alicat has transitioned to recommending the leak checking method described below, which requires only a single device. The result is a leak check which is faster to set up, take down, and operate, and is lower cost, all because it requires fewer pieces of equipment.

The faster, simpler leak check method

Leak Checking Setup with Alicat Whisper Gas Mass Flow Meter

Leak checking setup using a Whisper-Series mass flow controller configured to act as a pressure controller and measure flow.


When the DUT is subjected to a constant pressure within a closed system, any resulting flow is a direct measure of the DUT’s leakage. Stable leakages are best revealed and measured when the meter used for measurement generates minimal pressure drop (the frictional resistance that the device introduces into the gas line), as this will best ensure that all flows are fully measured. Whisper-Series devices have full-scale pressure drops as low as 3.6 mbar (0.052 PSID) and turned-down pressure drops as low as 0.018 mbar, which allows for precise and responsive control with minimal frictional resistance.

The leak test described in the video requires stable pressure control at the DUT and relies on accurate flow measurements to test for leakage.

To leak check smaller test volumes such as valves or sensors, a single Whisper-Series mass flow controller can be set to control for pressure. Configured this way, the Whisper serves the functions of both a pressure controller and a mass flow meter in one device. It will maintain a constant pressure at the DUT while providing accurate, real-time mass and volumetric flow readings, making it simple to characterize these components.

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