The first diving suits used a heavy copper diving helmet with windows and a hose from an air pump. The helmet was clamped to a waterptoof diving suit. Divers would wear heavy weghts and walk on the seafloor as it was not safe to swim. The air hose would send air to the helmet from a pump on land or on a boat above the diver. The air would pass trough the helmet and out into the water through a valve, and the diver would breathe from the air in the helmet. This wasted a lot of air, but there was no way to only supply air when the diver needed it. This is called a free-flow system.