I worked for the long gone Leyland Bus Company in the 1980s and spotted some new, mushroom shaped air valves in the scrap skip, (boy did they throw away some gems). Checked my components cattalogue and found they were automatic drain valves for Truck and Bus air tanks. Fitted one to the air compressor in our workshop, we mended the fork lifts, and needed more than the 90psi from the factory air main for tyres, it seemed to work fine, even gave one to the foreman in charge of the factory air compressors, he was leaving the drain cocks always slightly open at the time, don't know if he ever fitted it.
