For the maser to work properly, it needs extremely low temperatures -- around 4 degrees Kelvin, or -452 degrees Fahrenheit. In order to maintain this level of cooling, compressed helium is pumped through this expansion valve, which expands the helium, lowering its energy level and thus cooling it. Read More http://www.wired.com/science/space/multimedia/2008/05/gallery_jpl_goldstone?slide=7&slideView=5#ixzz13Qccja7X