If you have a valve which isn't going to get used, try playing with it. Make sure you can blow through it when you think it's open, and not when you think it's closed.
I'm trying to remember from when my dad had one. Although the valve body is a bog-standard quarter turn valve, I vaguely recall the lever had to be turned half a turn to open and close it, as the first quarter of a turn didn't turn the valve body, so if you were only turning the lever a quarter of a turn, it might not be opening and closing the valve.
Obviously, don't reuse a valve you've played with in this way, for risk of getting a UTI.