Are there any wires going into that thing? To me it looks like a solenoid valve. Wipe it clean and look for markings. Maybe remove it and cap the supply side, and perhaps the load side too, and see whether anything vital breaks.
If it has failed it needs to come out anyway, and finding a replacement whether sooner or later will be easier with the part in hand. Rather than waiting until you notice what's broken with that removed, you could instead trace the air lines to find out immediately.