Half-Turn to close the tank - why???

[dilligaf368]

The Tradition may have started in the Navy Diving. I'm not assuming that All handling of Pressure cylinders are from the navy diving but, that the training for divers may have started with the training of Navy divers. As the USN diving manule says: " ...the valve must not be used in the fully open position as it may stick or be stripped if force is used to open a valve that is incorrectly believed to be closed." Vol. 2-7-4.4
/b--------

 

[MoonWrasse]

The funny thing is that it seems so logical/habitual to do so without question, that even if it was never recommended to back off the valve 1/2 turn I'd do so anyway to avoid a frozen valve.

 

[Albion]

I've had one or two engineers over the years tell me that backing off a quarter turn is standard procedure with all valving, not just scuba. We should probably be asking engineers this question, not divers.
Steve

A lot discussed already but if you fully open a valve to the stop you are stressing the valve stem and possibly leading to a valve jam due to a diffenrtial pressure or temperature change. Whilst you may have carefully opened your own valve to the stop so it just hits someone else or some foreign object may hit the valve and wind it hard against the stop. Now you go along to test the position of the valve and find that it is tight, the assumption is that it is closed, with most scube this isnt a problem as with the valve fully open it is hard to release the first stage, however it could happen leading to danegous consequences. This can lead to slighlty more hazardous occurneces in petrochemical plants where high pressure gasses are involved - and as happened to a colleague who was trying to repair a pump at a sewage farm with very embarassing results, he assumed valve was off and opened up a main sewage line, the worst part was the fact he had to go back into the room to close the valve having run away once to get away form the spray :11:

So the best solution is to fully open then back off 1/4 or 1/2 turn that way valves tight to the touch are closed valves, loose valves are open and by a slight twist it can be confirmed they are nearly fully open.

YMMV

There are also some specialist valves in service which are designed to be cranked onto the back stop as there is a second seat, but these are usually tagged or lablled

 

[Trisha]

The way I figure it....
Who is going to turn a valve all the way, then back a half-turn, to get it closed?