Pillar valve

A pillar valve is the type of cylinder valve which is commonly found fitted to scuba diving cylinders. The name refers to the part of the cylinder, not to any part of the breathing set which the cylinder is fitted into.

Types of pillar valve

There are three types of pillar valve:
* A-clamp or yoke - the connection on the regulator surrounds the valve pillar and presses the output O-ring of the pillar valve against the input seat of the regulator. This type is simple, cheap and very widely used worldwide. A square pillar comes out of the cylinder neck. It has the air outlet and O-ring seating on one side. The old version had a small valve tap in its end: it had to be small because the A-clamp had to go on over it. Newer sorts have a bigger valve tap on one side as in the first image. It has a maximum pressure rating of 232 bar and the weakest part of the seal, the O-ring, is not well protected from over-pressurisation.
* "232 bar DIN (5-thread, metric M 25×2)" - the regulator screws into the pillar valve trapping the O-ring securely. These are more reliable than A-clamps because the o-ring is well protected, but many countries do not use DIN fittings widely on compressors, so a diver abroad will need to take an adaptor.
* "300 bar DIN : (7-thread, metric M 25×2)" - these are similar to 5-thread DIN fittings but are rated to 300 bar working pressures.The new European Norm EN 144-3:2003 introduced a new type of valve, similar to existing 232 bar or 300 bar DIN valves, however, with a metric M 26×2 fitting on both the cylinder and the regulator. These are to be used for breathing gas with oxygen content above that normally found in natural air in the Earth's atmosphere (i.e., 22% –100%).From August 2008, these new valves shall be "required" for all diving equipment used with Nitrox or pure oxygen. The idea behind this new standard is to prevent a rich mixture being filled in a cylinder which is not oxygen clean. However in the new system there remains nothing except manual human procedural checking to ensure that a cylinder with a new valve "remains" oxygen-clean, and this is exactly how the current system already works.