RACA Journal August 2023 | Page 45

Support amplifies the sound of the high velocity gas escaping from or going into the system . This means that it does not matter what gas there is in the plant ; it does not even matter whether the leak is outward or inward as long as a pressure difference exists . This method works equally well if the plant is under a vacuum . This type of equipment is fairly expensive and is not in general use by the industry but rather in specialised applications .

NITROGEN CYLINDERS There are precautions to be taken when using nitrogen cylinders . A regulator must be used when pressurising with nitrogen . The pressure in a nitrogen cylinder can be up to 32 000 kPa and it is absolutely essential that a regulator with a pressure relief valve is used when adding the nitrogen to the system . Use of a nitrogen cylinder without a regulator will lead to accidents and possible deaths . The system can and will explode as the uncontrolled pressure increases rapidly .

THE PURPOSES OF LEAK TESTING AND THE CONSEQUENCES OF LEAKS IN THE SYSTEM No system can operate at maximum efficiency if there is leakage into or out of the refrigerant circuit or if the circuit is contaminated with air or moisture . If there is a leak in the system and the system is operating at a pressure below atmospheric pressure , air and moisture will enter the system . The air will cause the condensing pressure to rise above normal pressure and the moisture will cause acids , sludge and copper plating of the system . If the system operates at a pressure above atmospheric pressure the refrigerant will leak out which will soon cause a reduction in system capacity . If all the refrigerant leaks out and the compressor is kept running it may burn out because of lack of cooling by the refrigerant gas entering the compressor .

THE CORRECT LEAK TESTING PROCEDURE

• Step 1 : Introduce a detectable gas into the system , and pressurise the system to approximately 50 kPa ( g ). The gas used should preferably be the refrigerant with which the system normally operates .

• Step 2 : Increase the test pressure to 500 kPa ( g ) with nitrogen and test for large leaks .

• Step 3 : Increase the test pressure to 1 000kPa ( g ) with nitrogen and test again for leaks .

• Step 4 : Increase the test pressure to the appropriate test pressure and test the system for leaks , using the most suitable method ( s ) for the system .

Appropriate pressures are as mentioned previously , or the nameplate on some systems indicates the recommended test pressure . In this case this is the pressure to be applied . All manufacturers ’ instructions must be followed .

IN SUMMARY

» The procedure for leak testing should be conducted in a methodical manner . Each joint which is a potential leak must be tested . One method is to start at the discharge valve of the compressor and follow the pipes to the inlet of the compressor .

» When moving the electronic detectors , the sensor must be moved at a speed of approximately 2 cm per second . Moving faster than this will lead to smaller leaks not being detected .

» When using the soap and water method , each joint must be painted with the soap solution .

» When using the electronic method , the system must be pressurised first with the correct type of refrigerant ( usually the type the system uses ) to a pressure of about 50 kPa . » Leaks on flares may be fixed immediately by tightening ( not over-tightening ) the flare nut before carrying on with the leak test . Use the correct torque settings for R410A systems .

» All leaks found must be marked for later identification and corrective action .

» To repair a leak , the refrigerant or nitrogen must be removed from that part of the system - the entire system may have to be evacuated if there are no shut-off valves .

» When using the ultraviolet method , the surrounding light , if too bright , makes it more difficult to see the ultraviolet dye where it has leaked out . Thus , this method must not be used in direct sunlight .

» To evaluate the leak test , all joints must be checked , and the system pressure must be observed . Any reduction in pressure means that there is a leak in the system , which must be found . » In addition , a vacuum test should be conducted .

James , I hope that this helps with your refrigeration work . Leak testing is an important aspect , and all systems must be leak tested . After working on the pressure envelope of a system a new certificate of conformance must be issued with the pressure test results stated on the certificate .

Thanks to everybody for the overwhelming response . I receive on average over 60 questions each month and cannot publish all of them . But keep them coming , as I may answer you directly . Looking forward to hearing from you . RACA

Grant Laidlaw

Thank you for all for your interesting questions . Send your problems ( and sometimes your creative solutions ) to acra @ netactive . co . za with ‘ Solutions Page ’ in the subject line . You may include pictures .