Leakage measurement system is a common teting device in a vast range of industries like auto industry and also hydraulic and pneumatic, medical, vessel and tank producer ones, to evaluate the faults of isolation. They exist in a veriaty of types which are deferent in their measuement methods.
Dry-Air and Wet Methods
A number of leak-detection methods are used in manufacturing auto industry parts. The most common methods are the various dry-air test methods. In these tests, an object is pressurized (or evacuated), then monitored to detect any leakage. Leaking is indicated by a change in pressure.
The dry-air technique acquired its name because it replaced the wet methods that are still prevalent in many industries. Wet testing is an inexpensive and straightforward approach. It involves elevating the air pressure inside an object and then submerging it into a water bath or brushing soap bubbles on the exterior and watching for the formation of bubbles. Though such techniques are acceptable in some applications but the wet testing medium can contaminate the part. Further, the process is highly susceptible to operator error and is difficult to automate.
The original dry-air method is pressure drop, in which the test part is pressurized and then isolated from the pressure source. Because air moves from a high-pressure area to a low-pressure area, any decrease in pressure indicates the presence of a leak. Algorithms then convert pressure changes into an approximation of the rate of leakage.
Pressure-drop testing can have a long cycle time, which might be problematic for high-volume production facilities. Because of the compression heating effect, the initial pressure measurement must be delayed until the temperature has stabilized. After stabilization, an additional time interval must elapse between this initial measurement and a second reading. This interval allows sufficient time for a measurable amount of leakage to occur. The longer the interval, the more likely small leaks will be detected. However, the relationship between test duration and sensitivity is not linear. For example, if a hole size were reduced by half, the testing would take at least four times longer to detect it. Therefore, time delay presents a practical limit to the sensitivity of pressure-drop testing.
A similar method, vacuum drop, evacuates air from the test object. For this method, it is the loss of vacuum that indicates a leak, rather than the loss of pressure. Unlike pressure drop, the vacuum-drop method does not require a delay for temperature stabilization because there is no compressive heating effect. However, it does take more time to evacuate the air from an object than to fill it with high-pressure air, although the difference is minimal for the small volumes of most parts.
To address the long cycle time, a faster approach has been developed, known as the differential-pressure method. With this method, a leak-free reference volume is pressurized along with the test part. A transducer then reads the difference in pressure between the nonleaking reference and the test item over time. Algorithms convert this difference into a volumetric measure of the leakage rate.
In this center we designed and manufactured a high precision dry air leakage measurement system using pressure-drop method. Please visit the relative pages to find more information and videos of this device.