Scuba manifold

A scuba manifold is a device incorporating one or more valves and one or more gas outlets with scuba regulator connections, used to connect two or more diving cylinders containing breathing gas, providing a greater amount of gas for longer dive times or deeper dives. An isolation manifold allows the connection between the cylinders to be closed in the case of a leak from one of the cylinders or its valve or regulator, conserving the gas in the other cylinder. Diving with two or more cylinders is often associated with technical diving. Almost all manifold assemblies include one cylinder valve for each cylinder, and the overwhelming majority are for two cylinders.

Several configurations are used, each with its own range of applications, advantages and disadvantages.

Longer and deeper dives require a greater amount of breathing gas, in turn requiring higher filling pressure, a larger cylinder or multiple cylinders. A large diameter cylinder tends to move the diver's center of mass further from the centreline, making them unbalanced in the water, and a higher pressure cylinder has a similar effect, also reducing the buoyancy of the diver, due to the thicker metal required for strength. Cylinder length is also limited by ergonomic considerations in proportion to the height of the diver. A single cylinder also presents a critical single point of failure for the breathing gas supply. Multiple-tank configurations include downstream manifolded twins, with a single regulator, independent or separate doubles which are two cylinders clamped to a backplate, but without a manifold, side mount cylinders, or upstream manifolded twins, with two complete regulator sets, which may have an isolation valve.

The manifold functionally combines usually two, but occasionally three or more cylinders in a way that allows the combined contents to be delivered to the diver through usually one or two regulators. Any arrangement that will perform this function is theoretically possible, but there are only a few arrangements that are commonly seen in practice, and these are a rigid assembly comprising a combination of cylinder valves, manifold connector tubes, isolation valves and reserve valves, with a connection to each cylinder at the neck thread^{[broken anchor]} and an outlet connector for each regulator. A fairly rigid support system to carry the cylinders is also needed, but is not normally part of the manifold system. In practice, scuba manifold systems connect the cylinders at storage pressure, the pressure can be balanced between cylinders, and the cylinders can be simultaneously filled through the manifold from one filling connection. It is usually possible to isolate cylinders from the manifold or from the outlet connectors, and the gas mixture is, as a general rule, the same in all of the cylinders. 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.

On an upstream manifold the left and right cylinder valves allow the corresponding first stage regulator to be shut off, leaving the entire gas supply to be used through the remaining regulator. On an isolation manifold, the central valve, called the isolating valve, separates the tanks into two independent systems, each with its own first-stage and second-stage regulators, which can prevent an upstream failure in one half of the system from losing the entire gas supply.

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. These were downstream manifolds, which connected the cylinders together by linking the outlets of the cylinder valves, and had one outlet for a regulator. This arrangement allowed larger gas storage capacity using the limited range of cylinders available. Independent valving of the manifolded cylinders also allowed the gas supply to be monitored in the absence of submersible pressure gauges, by opening and closing the valves in a specific order, as the gas was used up. 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. This also has limitations, even when the contents can be closely monitored by using submersible pressure gauges. 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. These allowed upstream connection of the cylinders, with a regulator on the valved outlet of each cylinder.

A manifold in fluid mechanics is a pipe fitting or similar device that connects multiple inputs or outputs. In this application: