Pre-charged tanks have several advantages over plain steel or galvanized tanks. Pre-charged tanks require less maintenance because the air and water are totally separated by a liner, so water cannot absorb the air and cause the tank to fill with water. If the tank is filled with water (a condition called waterlogging, the pump will cycle with every demand because there is no air pressure for the switch to sense. Although standard tanks can refill the air with air charging devices or can slow air absorption with a free-floating air barrier, these are not as reliable as the total air separation in a pre-charged tank.