The problem with any chemical that will attack the mineral deposits (typically calcium) is that it will also attack the brass -- in particular by leeching the zinc out of it, leaving holes in the "matrix". Leaving your valve exposed to acetic acid (vinegar) will definitely do this. I know because I came very close to causing some damage to one of my instruments in this way.
On the other hand, a common and recommended way of cleaning rotary valves of deposits is to dip them in muriatic (hydrochloric acid) for a few seconds. There's a good Youtube demo of this.
The key lies in how strong the acid is and how long the exposure is. Barry's recommendation of about 20 minutes for concentrated ascetic acid seems about right. Do not do something like letting valves soak in acid over night. Bad idea.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)