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Leaking (Bypassing) Valves
We had a class with our refrigeration techs and the topic of leaking and bypassing service “angle” valves and ball valves came up. One of the techs pointed out that most valves recommend loosening the top nut on ball valves and the packing nut on angle valves before turning the stem for maximum longevity of the valve and ease of turning.
It is worth noting that on angle valves you need to be careful not to back out the packing too far, just loosen it and then retorque it down when finished with use.
Mueller also points out that when brazing in packed service valve the valve should be mid-seated to prevent the seal from sticking together in either the open or closed position as well as keeping a wet rag wrapped on the valve to keep the valve temperature below 300 degrees.