How does a TRV work

[trigger25]

Apologies if this is a double post, I thought I had posted a message but I can't see it.

I had a radiator which wasn't getting hot and on closer inspection I found the locking nut was loose. As no water was leaking I unscrewed it completely. What I found was a valve with a central pin slightly protruding so not wanting to make things worse I replaced the TRV top. Having tightened it I found it started to work. As I could see no physical connection between the parts I was curious as to how the device works.

Thanks
Trigger

 

[Dotty]

Wax bead in the head expands with heat and depresses a plunger which in turn presses down the pin which closes the valve.

Different settings on the head denote different temperatures.

 

[trigger25]

Thanks for the explanation.