One of the many things that can go wrong with a tractor trailer: the brakes (and several other systems) are powered by compressed air. The air comes from the outside world, of course. And that outside air tends to have moisture in it.
It's not uncommon for that moisture to collect in the bottom of the air tanks. If it stays there, you have to worry about it getting into the air lines and blocking valves or actuators at just the wrong times.
So every once in a while you try to get that water out of those air tanks. The truck usually has an "air dryer" to keep the moisture under control, but you don't trust it too much. So you open the little purge valve at the bottom of each tank and let the 100psi air blast out, bringing any water in the bottom of the tank with it. Usually only a teaspoon or so comes out, but that teaspoon of water really Shouldn't Be There, so you smile and nod and tell yourself you haven't wasted your time.
Today I got out of the truck and pulled the wire to open the valve on one of the air tanks. It hissed, and spat, and hissed and spat some more. Then spitting ceased and the hissing steadied down. I smiled and nodded and let go of the cable.
The valve continued to hiss. It wasn't supposed to do that. And if it kept hissing, I wouldn't be able to drive. Air is way too important, on one of these vehicles.
So I reached under the truck and fiddled. I twisted and pulled and pushed and yanked. My fingers started getting numb. Then the valve spit out a piece of ice the size of a BB. And the hissing changed and stopped.
I think I'll let the truck run more tonight. Heat can be a good thing.
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