What is valve called that releases air from airbags on tractor?

Mine is working abnormally. When hooked to trailer and pressure on air bags rises it opens up and leaks.
What is it called?

 

I’m the one asking here lol
Does it release air when bags are under pressure?

 

Several times tried to catch the leak unsuccessfully.
So, I have previous posts about my truck having problem with my air dryer. When going uphill it is working fine. As soon as I start descending, purge valve on airdryer starts purging every thirty seconds until it stops (I don’t know why… overwhelmed maybe) and air tank pressure goes up to 145 psi until Safety Valve starts releasing air. Yesterday at dark I stopped to take a look and something is leaking somewhere in rear suspension area.
My guess is at uphill angles this leveling valve is fine but leaks at downhill which would explain why purge valve starts kicking every 30 sec or less.
Is my theory realistic because I’m changing leveling valve tomorrow? Or am I wasting money?

 

When I’m unhooked from trailer,

No. It is leaking only when driving. Especially after uphill going downhill. Like I mentioned above, after downhill yesterday I stopped briefly to see what’s going on. Noticed vivid leak from rear side (constant leak). Was on very narrow street, nobody around, in the dark. So decided to find safer place. The next stop, leak is gone.