Ok, I have just been going down a similar trail. Or should I say just starting on the trail.. Working on my 35 ton lowboy, leveling valves are connected into pilot valves. My truck parts guys were eager to sell me new valves after I showed them a photo. I asked what they did, and they had no clue.
My trailer also has the option to by pass leveling valve if you needed to raise trailer for railroad crossing, etc.. the pilot valve from my under standing appears to be a quick valve as it is close to your leveling valve and takes minute fluctuation out.. Hope that helps, this is not gospel, but what I think I have learned so far, feel free to correct me.