Lessons My sidemount cylinder valve spun itself completely shut during a dive

[davehicks]

Trouble is that the valves were not hard to open and were not hard to shut, after I got them to turn in the off direction.

I don't understand your point. A tank valve knob is literally a square hole on a square peg. If the knob is "stripped", replace it. If it is hard to turn, the valve needs to be serviced. Tank valves are often ignored to the point of unusability when it is so easy to maintain. Anyone is capable of servicing a tank valve and the parts are over the counter.

 

[BRT]

I don't understand your point. A tank valve knob is literally a square hole on a square peg. If the knob is "stripped", replace it. If it is hard to turn, the valve needs to be serviced. Tank valves are often ignored to the point of unusability when it is so easy to maintain. Anyone is capable of servicing a tank valve and the parts are over the counter.

If you turn it wide open against the stop and the shaft in the valve shrinks from temperature drop it gets really tight, apparently. I never believed it, but I've seen something happen that makes an easy turning valve not turn at the end of a dive. As soon as it comes off the stop it turns easily. I obviously don't know for sure what is happening, but suspect it is what our instructor told us about 40 years ago

 

[davehicks]

If you turn it wide open against the stop and the shaft in the valve shrinks from temperature drop it gets really tight, apparently. I never believed it, but I've seen something happen that makes an easy turning valve not turn at the end of a dive. As soon as it comes off the stop it turns easily. I obviously don't know for sure what is happening, but suspect it is what our instructor told us about 40 years ago

I question this. Get the valve stem very cold and it shrinks, gets loose. There is only a single oring that seals the valve, and when that gets crusty turning the handle gets stiff and can even blow out the end in little bits of rubber.

 

[BRT]

I question this. Get the valve stem very cold and it shrinks, gets loose. There is only a single oring that seals the valve, and when that gets crusty turning the handle gets stiff and can even blow out the end in little bits of rubber.

I don't know. I always doubted it since I was told that. But I have seen several valves that were not tight to open seize open after a dive and when they finally moved off of full open they were smooth again. It has made me go back to reversing my valve slightly after opening it.

 

[Wibble]

Could it have rolled off whilst attaching the bungee? Especially if it wasn’t fully open.