Abstract: A check valve comprising a section of a drill string, a flapper valve positioned within and concentric to the section of the drill string, and a piston valve positioned within and concentric to the section of the drill string. The flapper valve allows fluid flow in a first direction through an inner portion of a cross-section of the section of the drill string and not allowing fluid flow in a second direction, and the piston check valve allowing fluid flow in the first direction through an outer portion of the cross-section of the section of the drill string and not allowing fluid flow in the second direction, where the first portion and the second portion of the cross-section of the section of the drill string are mutually exclusive.

Abstract: A check valve comprising a section of a drill string, a flapper valve positioned within and concentric to the section of the drill string, and a piston valve positioned within and concentric to the section of the drill string. The flapper valve allows fluid flow in a first direction through an inner portion of a cross-section of the section of the drill string and not allowing fluid flow in a second direction, and the piston check valve allowing fluid flow in the first direction through an outer portion of the cross-section of the section of the drill string and not allowing fluid flow in the second direction, where the first portion and the second portion of the cross-section of the section of the drill string are mutually exclusive.

Abstract: A check valve comprising a section of a drill string, a flapper valve positioned within and concentric to the section of the drill string, and a piston valve positioned within and concentric to the section of the drill string. The flapper valve allows fluid flow in a first direction through an inner portion of a cross-section of the section of the drill string and not allowing fluid flow in a second direction, and the piston check valve allowing fluid flow in the first direction through an outer portion of the cross-section of the section of the drill string and not allowing fluid flow in the second direction, where the first portion and the second portion of the cross-section of the section of the drill string are mutually exclusive.

Abstract: A circulation control valve includes a top sub having a bore, a body connected to the top sub and having a first fluid passageway and a second fluid passageway parallel to the first fluid passageway, the bore communicating with both the first fluid passageway and second fluid passageway, a one-way valve in the second fluid passageway, and a first activatable block for the first fluid passageway. Upon upon activation of the block, fluid in the first fluid passageway is blocked and only flows through the second fluid passageway.