I believe that what you're describing is the automatic condensation drain valve that the big GE's are equipped with.
It sounds almost like a large electrical arc or zapping noise.
From what I understand, it doesn't so much limit pressure in the reservoir (the cutoff on the compressor does that), but rather it just eliminates the need for someone to periodically perform a manual process to drain the condensation.
I believe what you're looking for is called a spit valve -- it releases air from the tank in very short bursts when the pressure gets too high.
Usually that is the air pump cutting out. Check the manual for your decoder. Digitrax has the manual. All the air pumps I have ever worked with do that.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
I am looking for a specific sound of which I will try to describe. I want to see if I can program it into my AC4400's using Digitrax SDH104K1A+FN04K1 COMBO decoder.
While I was watching a youtube video I beleive the AC4400 was sitting still and it almost sounded like a brake or air release of some kind..
It was a very short spitting sound or clicking sound and happened about every 2 or 3 seconds.
I'm not sure what I'm looking for nor can I find the video I was looking at !
Any thoughts would be appreciated! (In case of spitting).