Manual Air Release?

[kofi2003uk]

Hi everyone, can someone please explain how this works. Please see picture. I suspect it’s some sort of manual air release? If so, can it push air around the whole heating system if the air is not let out?
I turned it anti clockwise for about 2 seconds and had a strong hiss (of air, I suppose) and closed it immediately.
Could this air be causing air in some radiators? I have 1 small radiator near it on first floor, which makes noise (popping usually) and usually has air in it
1- should I open this bit at the tip of that pipe to let the air out , just like bleeding any radiator? Should this be bled like the other radiators ?
2- could this air be going round the whole heating system if I don’t let it out?
3- could it be why this small radiator near it makes these popping noises especially when heating first come on? I initially thought might be just the radiator expanding with heat on but makes noises intermittently when already hot

Thank you

 

[danfre]

It's on the primary circuit, hot water cylinder. Air can get trapped around the coil hence the bleed valve.
The water in the heating system is common to heating and hot water cylinder .
If you need to bleed the system have boiler off and open the zone valve's manually

 

[kofi2003uk]

Thank you. So turning the brass tip to bleed it effectively bleeds the whole system. And just like any other radiator, water will leak out once all the air is out?
Been bleeding my rads every winter but have never touched this brass tip bit. Sorry if am being a bit silly with these questions

Many thanks

 

[danfre]

Yes , as said it is mainly for the water around the coil, no problem bleeding it when your bleeding the radiators

 

[kofi2003uk]

Many thanks