Mystery device in airing cupboard on open vent system.

[Meza]

Can anyone identify this device on my heating circuit, just before the pump?
I've often wondered what it does but never worked it out

View attachment IMG_20171022_220112.jpg

 

[ShaunCorbs]

Aerjec

 

[sammathias]

Air seperater isnt it?

 

[Last Plumber]

It is just that.

Always makes me wonder, when I see one!

 

[Meza]

Thanks all for the identification!