Apek's simple yet extremely effective Freeflow Control Device contributes a significant advance in diver safety. 
With the FCD fitted to your regulator, a simple sliding action allows the diver to isolate the freeflowing 2nd stage and continue the dive using a secondary air source, or alternatively, the diver can manually control the air flow allowing a safe ascent to the surface.
Designed to fit all regulators that use the standard 9/16" UNF hose fitting.