Double Flapper Check Valve With Lock-out Sleeve

Provide a lockable double flapper check valve. 

During the velocity string operation, this tool is connected between the joint and the lower plug device, and the double flapper check valve is in a forced open state. 

When it is necessary to retrieve the velocity string, the double flapper check valve can be activated by ground ball dropping to achieve the function of sealing inside the pipe and safely retrieve the pipe.