Are those electrical wires going into the valve?
It's hard to tell from the photo - how many air lines are connected to it?
If it is screwed directly into the ir tank, then maybe an automatic tank water drain with heater (like this style) https://www.anythingtruck.com/product/061-284412X.html
Or if air lines go to brakes and there are multiple valves, maybe part of the ABS system (if you have antilock braking).
Perhaps you can post some more photos of the valve from different angles.