need help valves sticking

why is one of my valves sticking but only when the tank has a good amount of pressure in it... it is on my train horn and is really annoying.. only time i use the horn is when i need a horn because the truck doesnt have one but i dont want to drain half the damn pressure out of my tank when i use it.. what would cause a valve to stick and how to i fix it?

What kind of valve and what kind of pressure are you running? I know sometimes my buddies 3/8" smcs stick when he forgets to turn his compressor off and it has over 250 psi, since there aren't rated that high.

not sure what brand part number is SC666-15 if that helps it is rated it says 150-210 psi and my pressure switch cuts off at 200 but it doesnt have to be full to stick