I have always wondered why people dont use hot water bottles for spudwork.
Try it, it would be stronger, have an actual threaded fitting and woul be easier to use.
It would be rather large however.
And it expands in two directions, not all directions when inflated.
Oh wait, I see why, silly me.
Entirely New Valve Design (Balloon)
A test ball would make your plan easier. standard schrader valve and all,tougher than other options mentioned so far
still don't hear how you're overcoming the force of the barrel seal though
hope this helps
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still don't hear how you're overcoming the force of the barrel seal though
hope this helps

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"A lot of what is taken for engineering fact is nothing more than somebody`s opinion when you dig into it far enough."
Henry "Smokey" Yunick, 1923-2001
Henry "Smokey" Yunick, 1923-2001