How do you remove the valve from the powertube?

Take something long and skinny like and allen wrench and push it down the long skinny part of the powertube. If you can pop out the oring that seals the tombstone if not I havent had any probs. But anyways have the allen wrench rest on the oring or the endge of the valve and tap the allen wrench with a hammer. That should pop the valve out. Also some people take plyers to the the valve pin and pull. Ive had issues with this method so I recomend the the allen wrench one.

Not a good idea to use a hammer, just get a big allen wrench, and push firmly.
the pliers work too but only if you have to because you can bend your valve stem.

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98% of paintballers...eh, who cares

Two safe methods that I know work:

1) Use the eraser end of a long pencil and push it out. Might snap the pencil depending on how tight it fits.

2) Wrap a small towel around the pin of the plunger valve and then use long nose pliers to pull it out. My preferred method.

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OK, once its out how hard is it to put back in?

Yup, noticed, my bad, i edited

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98% of paintballers...eh, who cares

...Edit, my bad.
...Fantastic Damage gave the correct answer, which is usually what I do. One change would be to use something non-marring (metal will scratch things), I use a peice of wood to push the valve out.

Remember, when you put it back together, "Washer first, then o-ring."

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My favourite valve removal method is just hitting the bottom of the powertube on a firm surface; towel on a counter kind of firm. The body of the valve gets loosened up and slides down to the point where the pin hits the surface you're using. A pull on the valve pin after that and the valve usually pops right out.

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Thanks for the tip, used the pencil method