NON-RETURN VALVE FOR CASING STRINGS Russian patent published in 1998 - IPC

FIELD: oil and gas well repair equipment. SUBSTANCE: non-return valve for casing string is provided with ball lock catcher located under valve seat and coaxially to it and to central bore of limiter. It is made in the form of pipe union attached to upper end of limiter. Pipe union has groove in internal surface for seating flexible sealing ring there. Internal diameter of sealing ring is less than diameter of ball lock. Lower wall of groove is located in common plane with largest cross-sectional area of ball lock in its lower position. Height of pipe union is larger than diameter of ball lock. Distance from valve seat to upper end of pipe union is less than diameter of ball lock. Aforesaid embodiment of non-return valve enhances its reliability when operating in inclined and horizontal wells in zone of their cementation. EFFECT: higher efficiency. 4 dwg