What part are you talking about?Air drier purge valve?Levelling valve exhaust?Help us, help you!Happy coaching!Buswarrior
Sounds like it could be a drain valve at bottom of tank. Did this just happen? Does it have a cable attached or air line/s? If air lines, how many?
If it looks like this, and hooked to bottom of tank, it is used to eject moisture automatically, every time air compressor cycles.https://www.amazon.com/Bendix-Automatic-Drain-Valve-281923RX/dp/B0045VITV2
Sounds like the purge valve on the bottom of the air dryer (which looks like an air tank) is stuck open.