Abstract: A differential float and cementing valve assembly used to position and cement casing in a wellbore. A leaf spring and other components of the assembly are preferably constructed of composite materials and/or plastics that can be drilled up with polycrystalline diamond compact (PDC) bits. The valve components may be contained within a metallic housing.

Abstract: A differential float and cementing valve assembly used to position and cement casing in a wellbore. A poppet valve mounted in the flapper gate of a check valve provides a regulated back-flow of drilling fluid through the check valve. A leaf spring biases the poppet valve to its closed position. Drilling fluid pressure in the wellbore overcomes the spring force to open the poppet valve and permit drilling fluid to back-flow into the casing. The regulated admission of drilling fluid into the casing permits the casing to sink into the well at a controlled rate while automatically maintaining a desired level of drilling fluid in the casing. With the casing at the bottom of the well, a cement slurry is pumped through the casing. A setting ball moving in advance of the cement slurry deactivates the poppet valve and its flapper gate and activates a second check valve in the assembly to prevent cement back-flow.