Unlike many lockshield valves which are just normal radiator valves with a different plastic cap, these are brass valves with a screw down (with spanner) brass cap. The brass cap contains a seal.
To adjust the valve you remove the brass cap and then use a screw driver to turn an internal screw.
I would like to buy some more of these, can anyone tell me a brand name (not Pegler!) or where they have seen one for sale?