In our previous post on inert gas leaks, we discussed the essential parts of the furnace system and the importance of ensuring zero percent leak tolerance in the backfill system.
Today, we will go over a few different methods for locating inert gas leaks: thin film (soap bubble) leak testing and vacuum leak testing.
Thin Film Leak Testing
The first method, which is the easiest and quickest way, is to spray a leak-detector solution on known suspect areas. If it starts to bubble in any places, you know you have found a leak.
Vacuum Leak Testing
The more precise method is to isolate the liquid nitrogen or liquid argon storage system from the furnace, ensure the entire system is in vacuum and then use a helium mass spectrometer to leak check the entire system.
To properly perform vacuum leak testing, you would:
- Close the outside valve. This isolates the outside liquid system from the evaporator stand, as well as from the backfill reservoir tank, the furnace and all of its ancillary partial pressure and backfill lines.
- Pump the furnace down, utilizing the furnace’s normal pumping system.
- Depressurize the backfill reservoir tank.
- Manually open the backfill valve on the furnace by electrically jumping it open.
Once you have opened the backfill valve and depressurized the backfill reservoir tank back to zero, the furnace will start drawing a vacuum on the lines, on the gas reservoir tank and on the evaporator stand – all the way back to the closed outside valve.
You can then use the furnace’s pumping system to pump the entire backfill system, as well as pull a vacuum on the entire system. Then, utilizing a helium mass spectrometer, you would leak check the entire system. Once you have identified all of the inert gas leaks with either method, you must go back and correct each of the leaks.
It is important to note that once you have corrected all of the leaks and put the pipes and lines back together, the entire gas system has been exposed to atmospheric conditions and ancillary water vapor. In our next post in the series, Finding Leaks in Your Vacuum Furnace – Part VII, we will examine the steps for bringing your furnace system back online after this has occurred.