Fitting thermostatic radiator valves in microbore system

I have a 1970s era 10mm microbore CH system in my 3-storey house. The radiators are fitted with double entry valves (at least I think that's what they are called - both pipes terminate at the same side of the radiator).

I would like to fit thermostatic valves, but I have not been able to readily find these. Are there in fact special valves for this type of system, or can I simply replace the outer valve body itself with an ordinary thermostatic valve?

I'm sure the answer to this would be obvious if I understood how these valves worked, so I'd really appreciate it if someone could please explain how the double entry valve functions

thanks

You will need to replace your twin entry valves with two separate valves at each end of rad, extending one of the two pipes to the other end of the rad.

Twin entry valves (which are still available, but not in a thermostatic version AFAIK) work by using a short tail pipe inside the rad to separate the flow and return water where they would otherwise mix.

Thanks. I had wondered if that was a solution - in fact it sounds like the only solution.

Presumably a task best left until warmer times, since the whole system would have to be drained and given that it woud be a more time consuming task per radiator than a simple valve changeout, this would be a laborious chore for a 13 radiator system.