The yoke connector, also known as an A-clamp or international connector, is a component of the regulator that fits around the valve body at the outlet and presses the outlet O-ring of the valve against the inlet seat of the regulator. The connection is officially described as connection CGA 850 yoke. The yoke clamping screw is screwed down snug by hand to ensure metal to metal contact between valve and regulator to sufficiently constrain the O-ring against extrusion. Overtightening can make the yoke impossible to remove later without tools. The seal is created by clamping the O-ring mounted in a groove on the face of the valve between the surfaces of the regulator and valve. When the valve is opened, cylinder pressure expands the O-ring against the outer surface of the O-ring groove in the valve and the face of the regulator inlet. This type of connection is simple, cheap and very widely used worldwide. Several O-ring sizes are in use, and both overall and section diameters may vary, but the correct size for the valve is necessary for a reliable seal and so that the O-ring does not easily fall out during handling and storage. It has a maximum pressure rating of 240 bar, and is not well protected against overpressurisation. Insufficient clamping force may allow the pressure to slightly stretch the yoke structure, opening a gap between the sealing faces of the valve and the regulator sufficient to extrude the O-ring through the gap, resulting in a potentially catastrophic leak. A similar effect can occur if the first stage is bumped against the environment, flexing the yoke enough to open a gap. When underwater this is most likely in an overhead environment where the diver cannot make an immediate emergency ascent. The risk of this cause for O-ring extrusion is roughly proportional to the pressure in the cylinder, and is less for a more rigid yoke structure. Older regulators may have a yoke rated at 200 bar, and these may not fit over more recent 240 bar valves.
