Effect of Test Pressure on Tightness Test;
It cannot be generalized that high pressure always shows better leaks.
At high pressure, more gas is released from the probable deformation area, but turbulent flow of the test fluid at high pressure requires longer dwell times. In addition, more stretching of the test piece and the reference piece, if any, at high pressure will negatively affect your test result.
Effect of Temperature on Tightness Test;
The pressure drop measurement method is affected by the ambient temperature, and the body temperature heating the product when the operator doing the testing touches the product. Increasing the temperature of the test piece also causes the test air to warm up, thus increasing its pressure. If this pressure increase is more than the effect of possible small leaks on the pressure drop, even if the tested part is defective, it can be detected as approved because the pressure drop is not at a sufficient level.
Effect of Expansion on Tightness Test;
The expansion of the test piece under pressure also causes the internal volume to increase, thus reducing the test pressure. This expansion amount, which increases in direct proportion to the applied test pressure, causes problems in distinguishing approved and faulty parts due to the pressure drop it causes. Since the material from which the test piece is made also affects this expansion amount, it is an important criterion for leak tests. This expansion continues indefinitely as an asymptote in theory. Significant completion of this expansion and the end of the turbulent flow of air before the test takes place within the period defined as stabilization, and the test process is started at the end of this period.
The “measurement method with reference part” can be applied for leak tests of materials such as hoses made of materials such as rubber, etc., where the expansion amount is high.
The Effect of Test Preparation Phase on the Leakage Test;
The products to be tested should be prepared for tightness tests, taking into account normal use and connection conditions. The possible forces to be applied during the closing process may adversely affect the tightness tests. In addition, since closing with flexible parts will directly affect the product volume, the effects of such closing situations should be considered during the testing process.
Because of these effects, 0.001mBar pressure drop detection can be accepted as the practical limit.
Although more precise measurements are possible, the measurement should be made in a temperature-adjusted laboratory environment, and there should be no movement near the test piece that will create air flow and contact should be prevented.
Working at these sensitivities for mass production lines requires a special set of applications. For such applications that require a high level of precision, different methods such as tracer gas and local tightness tests will be more useful in the mass production phase.