It is 17E taper thread. No O-ring but teflon tape in the thread. We have still such cylinders (Alu and steel) in use and also new valves from brass are made for both 200bar and 300bar pressure. New valve is just more expensive than those old firefighting cylinders. It is Interspiro cylinder in the picture. Not Inspo or some typo inspiro in the original message. Some old divers just want to look cool when training juniors in the pool.
Valve body dimension 19,8mm is more vulnerable for hits than new 3/4” and M25 O-ring seal designs. Some idiot must have decided to use M25 in Europe as the valve goes to 3/4” cylinder with force but some divers have almost died when the valve have got loose after some time. Now it is mandatory to have thread marking in the valve and in the cylinder. But no burst discs here. Some Alu alloy 17E valves broke after some hits in firefighting use.
Cleaning of those cylinders is difficult as the hole is so small.
We need hydro only every 10 years. It is so cold here that corrosion and other aging processes hibernate in winter.
