The compression tank has been used for many years, and in some systems has worked very well. Using a plain steel expansion tank makes the systems an air control system. One must control the air volume or air cushion above the water level in the tank. The common face between this air cushion and the water in the tank allows the air to be absorbed by the water. If the air is not removed properly from the water and placed back into the air cushion, the compression tank will become waterlogged.