Overpressure Leak Testing 
During a pressure leak test, a higher pressure is created inside the object being tested compared to the surrounding environment. In the case of a leakage, the medium (tracer gas) inside the object will escape into the surrounding environment, and the leaks can be detected using the appropriate techniques. 

Direct Sniffing with Tracer Gas 
In most cases of pressure leak testing, helium gas is used as the tracer gas to detect leaks. The principle is based on creating an overpressure inside the object being tested by filling it with helium gas. A sniffing probe is then used to scan the surface of the object for the presence of helium. If there is a leak, the helium gas will escape and can be detected by the sniffing probe. This allows for the identification of the leak location. This principle enables quick and direct detection of leaks using helium or other tracer gases, such as hydrogen.  

Accumulation Method with Tracer Gas 
In helium leak testing using the accumulation method and a sealed or fixed volume, helium gas is used as the tracer gas to detect leaks. The principle involves filling the sealed or fixed volume with helium gas and then waiting and accumulating. If there is a leak, the helium gas will slowly escape and accumulate in the sealed or fixed volume. Over time, the concentration of helium can be measured using a helium detection system, such as a mass spectrometer. A higher concentration of helium indicates a leak in the object. This method allows for the detection of the presence and size of leaks through the accumulation of helium gas.