An air lock is gas trapped in a high point of a liquid-filled pipe system. The gas, being lighter than the liquid, rises to the highest point and restricts the flow of liquid. In very tall systems, the gas can prevent flow entirely.
Flushing the system with high flow or pressures can help move the gas away from the highest point, or a tap can be installed to permit the gas to be vented.
Space station Alpha gets new air lock Robot arm, shuttle astronauts install $164 million module, making spacewalks easier
Jul 16, 2001; CAPE CANAVERAL, Fla. Two teams of astronauts installed a brand new entry on the international space station Sunday, then swung...