What is this valve and how do I use it?

[Banjo Bud]

I’m at my dads house and he has hot water heat. The hot water tank needed a new pressure relief valve so I had to drain a few gallons from the tank to install a new valve. Then of course I had to get air out of the system as i refilled it. I did that by opening the pump at one end. All went well but this small valve atop the expansion valve has me stumped. Am I supposed to open the thumb nut and leave it open or do I keep it tight? Sometimes when I open it a little air comes out but other times nothing comes out. And water never comes out.

 

[Weekend Handyman]

I am not a plumber. It is an air scoop with an high point air vent intended to eliminate bubbles from your system so the oxygen does not rust out your boiler. I would loosen the screw piece on mine to let the air out but would otherwise (i.e. when not standing in front of it) keep it tight.

Here is some info (likely not the exact one) https://www.tacocomfort.com/wp-content/uploads/2019/08/TD11_air-elim-hyd-systems_2015.pdf

 

[Sponsor]

 

[Banjo Bud]

Thanks. I just read all of it. So does that mean that I leave the thumb nut tight and somehow it’s spring loaded to release air? There is a rubber gasket in the bottom of the nut and the nut top has slits on the sides. I’m thinking that the gasket gives way at a certain psi to expel air. Is that how it works? Right now I have the nut snug but not tight.

 

[John Gayewski]

You leave it loose for a while. Then when all of the air is gone you can tighten it up.

 

[Banjo Bud]

Ok thanks

 

[Fitter30]

Auto air bleed has a float with a needle valve. Full of water valve is closed, air float drops valve opens till water displaces the air.