Hey First time on here, hello! I am planning to swap out a couple of Radiators soon and will be draining down the system. Before any work I like to understand the the system, so have been looking around and drawing up a rough schematic. I am pretty happy, apart from one item, the silver cylinder in the photo. It has a feed and expansision pipes, a pipe to the pump and a 4th that disappears into the wall. I'm guessing it's some sort of circulator/ valve but would like to understand its purpose before I continue. I am not trade, but am pretty competent I think. Thanks in advance
And a linky: https://www.tfc-group.co.uk/tower-products/heating/valves-motors-accessories/air-separator/ Spec sheet gives you some more details about them.