Yes, it has an expansion tank. See photo below. I does over time drop to zero, or at least to 2 -3 psi. There are four loops, each about the same length. Each has a cutoff valve so it can be isolated. The pressure when running drops about 8 psi, then back up when idle.

When I first filled the system, I filled one loop at a time, running it for quite a while to ensure all the air was removed. I actually closed the air bleed valve for a few days after running the system for a month or so. Then I opened it and it had a small amount of compressed air that hissed out. I have periodically checked it the same way and have not noticed any hissing sounds for the past year. Not saying there isn't air being released, just no enough for me to hear it.

I did just read on the internet (where everything is true and accurate) that you should not have the expansion tank pointing up like mine is, but hanging down in order to keep from creating air pockets.


Manifold.jpg