A J valve is almost identical to a K valve but is equipped with a lever on the hand wheel allowing for a reserve pressure. It was used before submersible pressure gauges become easily available. Today J valves are not in use for recreational and technical diving anymore and limited to very specific circumstances by military, commercial or other specialized diving.
Cylinder
K valve
The K valve is the most common scuba cylinder valve. It has one knob on the side perpendicular to the post. Its clockwise rotation close the valve. K valves have either a DIN or a Yoke connector for the regulator.
Burst Disc
A burst disc is a safety feature of cylinders valves to help prevent overpressurization. It will as the name implies burst with the excess pressure and drain the cylinder until it is at ambient pressure.
DIN – Deutsches Institut für Normung
DIN or “Deutsches Institut für Normung”, meaning “German institute for standardisation” is a word used to design tank valve and regulator first stage fittings. The other connection used in scuba diving is the A-Clamp or Yoke.