ACR Journal

February | March 2021 The requirements for the leaktightness of refrigeration and air conditioning systems are high. On the one hand, this is to ensure that the systems function properly during operation. On the other hand, to prevent the leakage of environmentally harmful and climate-damaging refrigerants into the environment. Unfortunately, many of the current testing methods are only partially suitable, or not suitable at all, to actually ensure the required leaktightness. Leaktightness requirements for refrigerant-carrying components As a rule, the loss of refrigerant may only be a few grammes per year. Cooling circuits with only small filling quantities logically also require smaller permissible leakage rates. For example, a leakage rate of three grammes of refrigerant per year corresponds to a tracer gas leakage rate – whether it be air, helium or forming gas – of about 3∙10-5 mbar∙l/s, depending on the type of refrigerant. Common testing methods on the test bench 1. Pressure decay test The measurement of pressure decay is probably the most frequently encountered testing method. The detection limits of this method are, in the best case scenario, about 5∙10-2 to max. 1∙10-3 mbar∙l/s. This therefore makes the pressure decay testing method too inaccurate for the leaktightness requirement of a refrigeration circuit by a factor of 100. Another problem: Common analog pressure gages usually have a large scale up to 20 bar. The smallest readable pressure decay of one pointer width is then in the range of about 50 mbar. A pressure decay of this magnitude occurs, for example, in a period of one hour for a system with a two-liter filling volume when the leakage rate is 2.8∙10-2 mbar∙l/s. This means that the pressure decay that LEAK DETECTION 32 Volker Trieb, Market Manager RAC at Inficon, provides a guide to improving process technology in refrigeration and air conditioning. Detecting even the smallest leaks a tester is just about able to read o the scale is already 1000 times greater than the limit leak rate against which testing should actually be carried out. In addition, a change in temperature during the measurement leads to a falsified measurement result, since there is a proportional relationship between the two parameters. 2. Pressure rise testing The pressure rise method is also frequently used in common refrigerant filling systems. However, the pressure dierence in this test can only be a maximum of 1 bar – the dierence between the atmospheric pressure of the environment and the vacuum inside the test specimen. Relevant leakages that only occur at an operating pressure of equal to or greater than 15 bar can hardly be found with this pressure dierence of one bar. 3. Foam testing Leak detection spray is often used to pinpoint leakages. However, only leakages up to about 1∙10-3 mbar∙l/s can be detected in this way. Leak detection spray is therefore unsuitable with regard to the leaktightness requirements of refrigeration circuits, as it is too inaccurate by a factor of >100. Another problem with this method is if the leak detection spray does not adhere suciently to the test specimen and drips o again or if, in the case of gross leaks, it is blown away as a result of the high pressure of the escaping air. Foam testing is understandably not suitable at all for places that are dicult to access or cannot be seen. After using leak detection spray, parts must be cleaned again. This cleaning eort is, of course, always required, even if the component was able to meet the leaktightness requirements. Volume 7 No.2 Automation level are increasing and require the integration of leak testing into the automated production process Foam testing: bubble formation at a leak The XL3000flex sniffer leak detector is suitable for both mobile use and robot applications