Tank Valve

The on-off valve at the top of a scuba cylinder where the regulator attaches, made in yoke and DIN styles.

The tank valve is the gatekeeper between 200 plus bar of stored gas and your regulator. Screwed into the neck of the cylinder, it opens and closes gas flow with a handwheel and provides the sealing surface where the regulator first stage attaches. The plain on-off design used across recreational diving is often called a K-valve.

Two connection standards dominate. The yoke or A-clamp system, common on rental gear worldwide, clamps the first stage over the valve against an O-ring rated for 232 bar service. The DIN system screws the regulator directly into the valve, captures the O-ring more securely, supports 300 bar, and is the standard in technical diving. Convertible valves with a removable insert accept both.

Open the valve fully and gently, and check gas flow while watching the SPG during your buddy check, because a barely opened valve can breathe fine at the surface and starve you at depth. Modular valves can also accept H-adapters or be paired via a manifold on doubles.