[1] Manifolds combining more than three cylinders are occasionally used for open circuit scuba depth record attempts.

The function of the most commonly used scuba manifolds is to connect the gas supplies of two back mounted cylinders (called doubles or twins), allowing the diver to breathe simultaneously from both.

[1] Manifolded twin and triple cylinder sets have been used since the days of Cousteau and Gagnan's development of the open circuit regulator, as can be seen from early photographs of the equipment.

The need to remember the history of valve operation and the lack of facility to connect a redundant regulator made the use of independent twins the usual alternative.

In 1970 a group of divers including Tom Mount, Ike Ikehara and George Benjamin came up with the concept and had the first recorded dual outlet scuba valves prototyped.

[2] A manifold in fluid mechanics is a pipe fitting or similar device that connects multiple inputs or outputs.

[3] The manifold structural components are usually machined from a high grade brass alloy,[4] and chromium-plated for corrosion resistance and appearance.

Brass is used because it is strong enough, acceptably corrosion resistant, easy to machine, and suitable for oxygen service.

Manifold lengths are available to connect different cylinder diameters, and centreline distance may be adjustable over a small range.

They are generally slightly less rugged than face seal manifolds, and more vulnerable to thread damage during assembly, as they use a finer thread pitch, but allow a small amount of cylinder centre distance adjustment, and provide a reliable seal even if not completely tight.

Plain manifolds simply connect the interiors of the two cylinders together, allowing gas flow between them at all times.

[1][6] Cylinder to manifold connection malfunction, though rare, can result in an extremely rapid gas loss.