RACA Journal August 2023 | Page 41

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GRANT LAIDLAW

Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy ( ACRA ) in Edenvale . He holds a Bachelor of Business Administration and an associate degree in educational administration . He has a National Technical Diploma and completed an apprenticeship with Transnet . He has dual-trades status : refrigeration and electrical . He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018 . Currently he is the SAIRAC national treasurer .

WELCOME TO THE

SOLUTIONS PAGE

By Grant Laidlaw

Many people ask for assistance in the understanding of theoretical and practical aspects of the industry . I will endeavour to enlighten . I am going back to basics as I have questions coming in which indicate that the basic understanding necessary to work in industry is not in place .

James sent us this question : “ Grant , with regards to leak testing , what would be the preferred method for hydrocarbons ? It seems that soap water will be the only safe way moving forward .”

Hi James , we all need to keep abreast of changing technology and this is certainly an area worth looking into . Having spoken recently to people in the industry and in particular rural areas , it became apparent that some of the basics skills are an issue . I even ran across some refrigeration mechanics using the old halide testers , explaining to me that they work well . Of course , leak testing on a system that uses a flammable refrigerant with a leak tester that utilises an open flame is really dangerous .

The vast amount of refrigerants in use globally coupled with fairly high leakage rates are creating environmental issues . Leaks can reduce system performance , lead to energy wastage , product and production losses . Leak testing is therefore an important

aspect of system installation and maintenance . Leaks should be located and attended to as a matter of priority .

The vast majority of refrigerant systems circulate oil when operating , and therefore when generally inspecting a system that has been running for a period of time , oil residue anywhere on the equipment or piping indicates a possible leak .

As this will not be the case with all leaks or on newly installed systems , a thorough leak test must be conducted .

The first step is conducting a vacuum test . In this test there will be no refrigerant in the system . Using a vacuum pump capable of reaching a vacuum of at least 500 microns , evacuate the system until the vacuum is below 500 microns . Isolate the system using your manifold gauges and observe the micron gauge placed after the manifold gauges . If , after a minimum period of two hours , the system has maintained the vacuum , one can conduct a pressure test . Two hours is a minimum , on larger systems it is recommended that the system stand under vacuum for a longer period .

For the following methods of leak detection , the system must be under a positive pressure utilising dry nitrogen . Only a small amount of detectable gas is required in the system to detect the leaks when using the methods that rely on monitoring the gas leaking out of the system .

Most leak testing instruments are sensitive to commonly used refrigerants although care must be exercised when selecting the instrument because not all instruments are suitable for the hydrocarbon refrigerants .

To minimise the amount of refrigerant for leak testing , the system is pressurised to about 50 kPa ( g ) with the refrigerant , with which the system normally operates . To bring the test pressure up to the test pressure required , dry nitrogen is added ( care must be taken that the pressure does not become excessive ).

You must use a nitrogen regulator and I mean ‘ must ’. If you decide to disregard this , I may be attending your funeral and I do not like funerals . So please use a regulator . Under no circumstances should compressed air , oxygen or acetylene be used for pressure testing .

It must be remembered that pressure testing serves the purpose of locating leaks and not that of testing whether the components can , in fact , withstand the pressure . If the entire system is tested , care must be taken that the pressure applied to the system does not exceed the maximum operating pressure of the components .

For pressure testing the entire system , including the low side components , the pressures recommended depend on the normal working pressure of the refrigerant and are as follows :

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