Air cylinders

Air cylinders used for scuba diving come in various sizes and materials and are typically designated by material (aluminium, steel, high-pressure steel, etc) and by how much air (in cubic feet) they contain at 1 atmosphere (80, 100, 120, etc). The most common is the "Aluminum 80", which will give an average experienced diver from 40 to 60 minutes of dive time under common dive conditions.

Air cylinder pressure will vary according to the type of material used, ranging from 2000 psi up to nearly 4000 psi.

Aluminium cylinders are less expensive than steel and have been known to last for 20 years with standard regular maintenance. The drawback is that aluminium cylinders are neutrally buoyant when full, and positively buoyant when nearing empty. This results in having to monitor buoyancy during the dive more closely so as not to experience the "express elevator to the surface". Aluminium tanks also need the diver to carry more weight. Divers often prefer to use steel tanks as they are negatively buoyant when full and neutral when empty. Many steel tanks also accept higher pressure fills, giving more capacity for a longer dive for the same size of cylinder.

Comments

RAWalker - 12/27/2007 1:56 AM First: It needs to be mentioned that there are aluminum tanks that are designed to be neutrally bouyant when empty. These type cost a bit more and are nothing more than cylinders with enough extra wall thickness and base thickness to make up the weight. Second: You really don`t carry more weight either way. The weight is either part of the cylinder or it`s on your belt/in your BC. That leaves the only real advantage to be high pressure cylinders can hold more. The down side is they generally also cost more.