Unknown component

[Stanios]

Just been to a loft and saw a weird little cylinder on the solar heating circuit.
I cant post pictures for some reason but its a small (4 litre or so) copper cylinder,with a bleed vent like one on a towel rail and the solar heating pipe goes in at the bottom comes out at the top.

I assume its something to do with air but it wasnt installed at the highest point of pipework also dont understand the need for the cylinder rather than a bleed vent on its own :confused5:

 

[gassafe]

Wasn't an expansion vessel was it?

 

[Dotty]

Shock arrestor.

 

[Stanios]

It looks proper dodgy looking at it shame cant post the photo. There is a vessel there but this thing is like half the size. Thought shock arrestors were only used on mains?

 

[Dotty]

Meant to be, son, meant to be. .......