Today I got a vacuum relief valve for my in-progress solar panel build. It didn't look like something I would expect. I'm used to float type of vacuum breakers used in hydronic heating systems, irrigations, etc.
When there is incoming water in the system it bleeds the air first and then water lifts the floater and seals the valve. When there is no pressure, the floater drops, opening the valve.
This one seems to be made out of mesh wire with a little thing sticking right in the middle (see the pic). Looking at the other side of the plug it seems that it has about an inch of wire mesh held in place with some plastic. That's it.
It seems to be air tight blowing into the tube and it allows some air very-very slowly when trying to suck the air out of it. I'm curious about how it works and what that mesh is for in particular. But I can't seem to find anything on this type on internet. I'm also somewhat concern how little air it lets in when it's supposed to be open. Maybe under normal condition it would work ok, but I can't really test it much at this point...