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does anyone on here have any experience with/knows what would happen if you took the springs from a piston valve tuba and stretched them out a little. it seems like it would make the valve spring back into place faster and with more force.

I have done it successfully on some tubas. But when I tried it on my little Weril I found that the spring went back to its original length after the valve had been depressed once. I blame that partly on cheap original-equipment springs and partly on the fact that the Weril designer did not leave as much spring room at the bottom of the cylinder as he should have.
It's a good idea to have an extra set of springs handy if you try stretching them, just in case it does not work out. First measure the spring's length. Then stretch it out, being careful not to bend it, and note how far out you pulled it. You can feel when it approaches its elastic limit, and you don't want to go much beyond that point. Measure it again after it springs back to see if you have accomplished anything. If necessary, pull it again just a little bit farther. Repeat until it is 10 to 20 percent longer than original. If that's not sufficient then shop around for heavier springs.

Spring design is a fairly exact calculation. Too much deflection causes fatigue. Too little deflection equals poor performance. If you want stiffer springs, buy some that are made with with heavier wire. Stock springs have fairly 'square' ends and cylindrical shapes. When you stretch springs, they sometimes tend to get out of that cylindrical shape that keeps them from rubbing the sides of the piston casings.

does anyone know where i can purchase a set of springs of a heavier gauge? the stretching business sounds kind of scary for me.

According to spring physics, springs will ALWAYS return to their original manufactured shape when they are compressed as long as it does not exceep the point of distortion. If that happens, their structure is significantly weakend.

Pretty much, physics dictates that your springs should never "fatigue" from normal use, and stretching them should not improve them...only wreck them if you stretch them too far. How much of this actually applies to the real world, I don't know, but I would strongly recommend just replacing the springs if you are not happy with them.

This is only my opinion, but I think spring stretching is a very risky, bad business, and I recommend to not do it. If a valve is that lackluster in performance, I generally find that it needs to be thoroughly cleaned and lubricated, and sometimes actually has been damaged. Even the cheapest tuba, if clean and in good repair, should have really good valve action.

Feel free to e-mail me privately about your particular make and model of instrument, and I can make a recommendation about good candidates for spring replacements.

To the respondent above with the Weril - Yamaha valve springs work well in Werils, if the originals are not salvageable. On some instruments, if the spring that gives the best action doesn't fit the bottom cap channel, which is fairly common on older horns, I chuck the bottoms caps in the lathe and enlarge the spring channel, so that it does fit.