Trailer suspension issue

Could that valve regulate the pressure coming out of the tank?

 

That is normal to leak. It is a regulatory valve, it's supposed to bleed off excess air pumped from the compressor. If it doesn't your bags will max out and the trailer will sit really really high.

After you cut the truck off with the trailer valve pushed in, that valve should level it's self and stop bleeding air. If it leaks to a point where the entire set of airbags deflate totally flat, then you have a bad leveling valve.

Warning!
I've ran across this problem many times with the DOT and they are just as confused as most are and also do not understand. It's something you'll need to explain professionally to keep you from getting shutdown

 

The valve on the tank is a relay valve. If that goes bad you will have a long delay before your brakes will apply, or release to your trailer when you step on the brake.

It will do strange things too like bleed air through your dashboard valves when you park when it goes bad.

If your having problems with brakes applying or releasing that is most likely the cause. It's a cheap part too, maybe $30

 

Few years late for an answer for your question, but those valves are added into the air suspension to dump the trailer suspension when the parking brake is set for loading purposes. They can be used for other reasons, but majority of the time they're used for that.

It's basically a secondary control valve for your air suspension other than just up and down function of your leveling valve when the trailer has air in the tanks. They can be electronically or air controlled depending on the valve style you have.