Scuba Tank / High Pressure Air Tank 7/8″ Valve Stem Replacement O-Ring

If you have a SCUBA or Pre-Charged Pneumatic (PCP) air tank that has a 7/8″ valve stem that is leaking where the tank and valve stem come together, it is probably the O-ring failing and you need to replacee it.

You also may have already experienced the frustration of trying to find the correct replacement O-ring gasket. How do I know it can be frustrating? Because I went through it. I have a 300 bar / 4500 PSI carbon fiber tank with a 7/8″ tank valve stem.

The correct O-ring matters a great deal and this means getting the material, size and hardness correct. These are not O-rings you buy in the plumbing section of your local hardware store.

Aftet doing research, I bought the O-rings with following specifications from my industrial parts supplier:

Material: Buna-N

Inside Diameter: 7/8″Nominal and 0.859″ Actual

Outside Diameter: 1-1/8″ Nominal and 1.149″ Actual

Thickness: 1/8″ Nominal and 0.139″ Actual

O-Ring Number Designator: 212

Hardness: 90A

These will do the job. I do recommend a light coating of silicone o-ring grease (never petroleum) on the O-ring during installation so it slide vs.tear during assembly.