answering your question irving the display i have in mind is maybe six indapendant 10 foot (above the stage platform)poles (well away from the crowd obviously) on oposite sides of the stage area giving off varying size puffs of flame (the max being roughly no more than 1 foot in diamiter) in line with the treble, mid and base,
this would preferably be run from a standard analogue light control unit but if another option is more viable then so be it.

as for the type of valve i am thinking of useing something like a simple quarter turn water stopcock, hob taps are o.k but not enough flow unless i try and modefy in some way