I've never considered the second valve slide to be a tuning slide, albeit its length does closer set the tone(s) of the second valve. For me, about all I can ascertain from it is the bore size of my instrument. Otherwise, on a trumpet seemingly it is about equal to extreme to that of the bell bow, but I've known this damage to be so severe that it jams the inner tubing into the second valve, seizing the second valve and in the extreme requiring the second valve and it's casing to extensive and costly repair/replacement. The scenario I've often seen that gives me the willies is students jamming their instructional books in the instrument case right on top of the second valve and then slamming the case lid shut. It would amaze me if the second valve slide survives this without damage.