Choosing the right valve depends on the positioning of the valve inlet on any given radiator.
Inlets can be on the bottom of the radiator (fig.1) or the side of the radiator (fig.2). Inlet position should be easy to ascertain from a radiator image, however, if in doubt do not hesitate to contact us on 0844 358 1995.
Choosing also heavily depends on what function you require from your valves. Building regulations strongly suggest that you have TRVs
installed on your system for efficiency and cost effectiveness and if all the radiators have TRVs you will also require an automatic bypass valve to prevent valve hammer and velocity whistling. That said manual valves are perfectly acceptable if you have decent boiler thermostatic control and often a preferred method for installers to provide manual system bypasses (i.e. a system includes both trvs and manual valves).
One final consideration would be to ensure you choose valve pairs with an actual lock-shield (fig.3) component. Lock-shields prevent the average radiator user from permanently adjusting your heating system's balance. Poor system balance can lead to radiators that just don't warm up, and others that get all the heat. A lock-shield is set once by your installer and then requires a tool (generally an Allen key) to adjust it in the future.