API 7-1 Drill Pipe Float Valve Float Sub

Drill pipe float valves, or non-return valves, are downhole safety valves that create barriers to prevent unwanted flow of fluids up the drill string.
The float valve locks down the flow of fluids while the crew at the rigfloor is making or breaking connections.
Specifying the optimum drill pipe float valve for oil and gas projects is critical - the different valve types extend further than a simple split between the F-type plunger valves and the G-type flapper valves.
For further reading and to view the complete article by Keystone Energy please visit :  7 Types of Drill Pipe Float Valves.