A standard controller may also work, however, stable leakages are best detected when the meter generates minimal pressure drop (line pressure due to frictional resistance). This makes the low-pressure drop (as low as 0.07 PSID) of a Whisper quite useful, especially when leak testing smaller volumes such as valves or sensors.
An Alicat mass flow controller simultaneously displays flow, pressure, and temperature readings and can control either flow or pressure. In the setup above, a single Whisper controller is able to maintain a constant pressure at the device under test (DUT) while providing accurate, real-time mass and volumetric flow readings. When the DUT is subjected to a constant pressure within the closed system, any resulting flow is a direct measure of the DUT’s leakage.
Watch the video below for a demonstration of the leak testing setup:
Alternative method: Flow meter and pressure controller
Historically, Alicat has provided two-unit leak testing systems using a standard mass flow meter and a remote sensing pressure controller. When plumbed as shown in the diagram, pressure is controlled at the inlet of the device under test (DUT). The needle bleed valve allows the pressure controller to hold pressure at the DUT.
If the bypass valve is closed and temperature is constant, the flow through the meter will be equivalent to the leak rate of the DUT. To reduce temperature fluctuations and make the process faster, you can reduce the dead volume between the flow meter and the DUT or reduce the volume of the DUT itself.
Note: This process may not be suitable for leak tests on larger volumes where the allowable leakage is near zero because minute temperature differences on large volumes can produce actual flows that are greater than the allowed leakage rate. This same problem of physics would also affect leak testing by pressure decay.
