BCD actually stands for “Buoyancy Control Device”. It is the device that often looks like a cross between a life jacket and a waistcoat that a Scuba diver wears on top of his/her wetsuit. It has a whip (hose) connected to the divers first stage (this is the metal piece that attaches to the top of the divers cylinder). This whip carries air at 1 Bar above the ambient pressure to the diver BCD. When the diver is in the water he/she may need to press a button on the BCD to inject air from the cylinder to the BCD thus aiding the diver in controlling buoyancy. The diver usually needs to be neutrally buoyant in the water so the BCD is used to do this. There is also a “Dump valve” on the BCD to dump air. When a Scuba diver enters the water you may see him/her holding a hose in their arm upright as they first leave surface. This is the dump from the BCD to force the air out to aid decent. There is also an additional independent cylinder on the BCD to do inflate so that the breathing air does not need to be consumed.
Now that you know what a BCD is and how it works, watch the video to see how it is made.