A diving compressor is a machine that is capable of either filling tanks with breathing gas, or directly supplying divers by means of an umbilical. These devices can be portable or installed permanently, and are operated by either electric or gas powered motors. The main component of a diving compressor is typically a three or four stage air compressor, though they typically also contain a variety of filters. This is due to the fact that breathing gas must be exceptionally pure, so there must not be any significant contamination from lubricating oil, carbon monoxide, or water. The other component that is often found in a diving compressor is a mixing board, which is used to introduce various gasses such as nitrogen and helium to make different breathing gas blends.
There are two different ways to supply people with breathable air when they are underwater for extended periods of time, and both of them require a diving compressor at some point. One of the common methods of supplying divers with breathable air is tanks, which the divers carry with them. These tanks differ in both size and composition, and can hold varying amounts of breathing gas depending on the application. In order to purify air and fill a tank with it, a diving compressor is needed. The same is true for surface-supplied divers, who get their air directly from a land- or ship-based compressor.
In order to fill tanks, or pump breathing gas underwater, a diving compressor typically must include a three or four stage air compressor that is designed specifically for that purpose. Unlike other air compressors, these devices have safeguards to keep contaminants from entering the compressed breathing gas. Different filtration methods are usually employed to prevent lubricating oil, water, and carbon monoxide from entering the breathing gas, since these contaminants can present issues for divers. Some simple surface-supplied diving operations use compressors that are scavenged from other sources, which can lead to increased health risks for the divers.
Beyond certain depths, special breathing gas blends are typically required to ensure diver safety. Some common blends include trimix, made of oxygen, nitrogen and helium, and heliox that consists of helium and oxygen. Diving compressors are sometimes capable of taking these component gasses from storage cylinders and combining them in the necessary ratios. This is usually accomplished with the help of a mixing board. In some cases, surface-supplied divers will get their air from ship-based breathing gas reservoirs that contain these mixtures pre-mixed.