Purpose
An o-ring forms a seal linking two components to allow the flow of gas between them. O-rings are found in three locations on a SCUBA tank: the tank neck, inside the pillar valve and the regulator seat on the tank valve (or pillar valve).
Sizes
Scuba o-rings range in size with the smallest (11/16-inch outside diameter) found inside the cylinder valve bonnet nut and the largest sealing the tank neck (1 1/4 inches outside diameter).
Materials
Most o-rings used on air cylinders are made from synthetic rubber (nitrile). For oxygen-rich cylinders, fluoroelastomer (viton) o-rings are used to reduce the risk of fire.
Tank Neck O-Ring
The tank neck o-ring seats between the pillar valve and the cylinder opening to create a seal.
Pillar Valve O-Ring
The pillar valve o-ring is located inside the valve that controls the flow of gas out of the cylinder.
Regulator Seat O-Ring
This o-ring seats between the regulator first stage and the tank valve to allow gas flow out of the cylinder. The DIN regulator screws into the tank valve to trap the o-ring securely.
