the water droplets to bond to as they freeze. External mixing guns are typically tower guns and rely on a longer hang time to freeze the snow. This allows them to use much less air. External mixing guns are usually reliant on high water pressure to operate correctly so the water supply is opened completely, though in some the flow can be regulated by valves on the gun. Fan guns are very different from all other guns because they require electricity to power a fan as well as an on-board reciprocating piston air compressor; modern fan guns do not require compressed air from an external source. Compressed air and water are shot out of the gun through a variety of nozzles (there are many different designs) and then the wind from the large fan blows this into a mist in the air to achieve a long hang time. Fan guns have anywhere from 12 to 360 water nozzles on a ring on the front of the gun through which the fan blows air. These banks can be controlled by valves. The valves are either manual, manual electric, or automatic electric (controlled by logic controller or computer). Snow lances are up to 12 meter long vertically inclined aluminum tubes at the head of which are placed water and/or air nucleators. Air is blown into the atomized water at the outlet from the water nozzle. The previously compressed air expands and cools, creating ice nuclei on which crystallization of the atomized water takes place. The height and the slow rate of descent allow sufficient time for this process. This process uses less energy than a fan gun, but has a smaller range and lower snow quality; it also has greater sensitivity to wind. Advantages over fan gun are: lower investment (only cable system with air and water, central compressor station), much quieter, half the energy consumption for the same amount of snow, simpler maintenance due to lower wear and fewer moving parts, and regulation of snowmaking is possible in principle. The working pressure of snow lances is 20-60 bar. There are also small mobile systems for the home user that are operated by the garden connection (Home Snow). Home snowmaking Smaller versions of the snow machines found at ski resorts exist, scaled down to run off household size air and water supplies. Home snowmakers receive their water supply either from a garden