I've been diving with a 3-litre pony cylinder which is attached by a metalsub to my main cylinder. The problem that I have with this is that it is very difficult to reach over my right shoulder to open it due to my short arm.

I'm thinking of 'inverting' the cylinder so that the valve is upside down which will allow me to open the cylinder.

Does this seem a workable solution. I'm open to suggestions.