Freeze dryer What to do after a refrigerant leak? The most obvious sign is a refrigerant pressure gauge reading of zero. Finding the leak requires patience, attention to detail, and a systematic approach. The specific methods are as follows: First, use visual inspection. Open the freeze dryer's casing and observe the interior. Because the refrigerant is in operation, compressor lubricating oil will mix with it. If there is a refrigerant leak, the lubricating oil will be carried out. Then, check the capillary copper tubes inside the freeze dryer, i.e., the thin copper tubes and process tubes below 6mm, for any breaks. After these basic checks, mark any questionable areas. Then, it is necessary to add an inert gas under pressure to confirm the leak. If possible, use nitrogen to maintain pressure; do not use oxygen to maintain pressure and check for leaks if nitrogen is unavailable. Using oxygen with refrigerant is prohibited.

　　When starting the freeze dryer, add gas slowly and increase pressure, observing the refrigerant pressurization (small units only have a low-pressure refrigerant gauge; units above 15 cubic meters have high and low-pressure gauges). Temporarily stop when the pressure drops to 0.2mpa (2.0kgf), then carefully listen for any leaks inside the machine. If there are any, use a funnel to drain the sound. If not, continue to apply pressure to 0.4-0.5mpa. Then, use a sponge dipped in soapy water to check the previously questionable areas, and then check all connecting pipes (copper nuts) inside the freeze dryer.

　　If there is a leak, bubbles will appear. This process requires extreme caution. If the above methods still fail to locate the leak, it is unfortunately likely that the evaporator is leaking. Evaporator leaks are more difficult to handle. First, it needs to be confirmed. This can be done by disconnecting the evaporator from the refrigeration system and then maintaining pressure separately to confirm. If the pressure drops after maintaining pressure separately, it can be confirmed. Another simpler method is to open the compressed air inlet. If the refrigerant pressure gauge rises after a period of time, it can also be determined that the refrigeration system is connected to the air system, because the part where they exchange is the evaporator. Therefore, we can also confirm the evaporator leak.

　　After finding the leak point, seal it. Depending on the leak point, for loose bell mouths, simply tighten them with a wrench. For copper tube welded leak points, brazing is required. Brazing is one of the commonly used techniques in refrigeration repair. Brazing involves using an oxygen and acetylene flame to heat a low-silver solder and the part to be repaired, causing the solder and the repaired part to fuse together, plugging the leak. Before brazing, the refrigeration system should be depressurized and discharged. Then, use a brazing torch to open the acetylene, ignite it, and add oxygen appropriately. Slowly adjust the ratio of oxygen and acetylene gas to make the flame a neutral flame—an oxide flame—then heat the required weldment and silver electrode, causing them to dissolve together. Specific methods require operators to undergo specific training. After handling the leak, the system needs to be pressurized again to confirm whether the leak welding is successful.

　　After filling the leak, vacuum the system and add the specified amount of refrigerant (see the basic configuration table for the specific amount). Add refrigerant from the dedicated liquid needle valve of the freeze dryer. For larger freeze dryers, refrigerant should first be added to the high-pressure charging port. If the specified amount cannot be added at once, it should be added slowly from the low-pressure port after startup.