Float valve unit is composed of body, sealed ring, seal gland, valve bonnet, torsional spring and limit marker.

Working principle of float valve is rather simple.When normal drilling and pumping circulation,the bonnet of float valve unit will be opened completely.If well kick or pumping off occurred,the bonnet will close waterhole depends on elastic force of torsional spring.It can prevent blowout in the drilling tool.

Float subs are used to house a float valve, also known as a back pressure valve. The float valve functions as a safety between the well bore and the inside of the drill string to prevent drilling fluids from back flowing up to surface.