T&T: Filling older propane tanks

[Bill]

I know less than a "little" about the propane business but I do know the
National Propane Gas Association calls the OPD the "most significant attempt
ever to improve safety in the filling of small propane cylinders"  

 

Also,  they say "Some of the early OPD valves had an insufficient flow
capacity for certain types of service such as high-pressure torch
applications. Market competition has resulted in OPD's becoming available
that have significantly greater rates of flow."  Not sure I understand the
effort to avoid getting a tank with an OPD.