A stage valve for stage cementing of casings in a well bore including a tubular collar and a telescopic tubular sleeve where the sleeve has a piston portion disposed in a collar chamber and the piston portion separates a sleeve port from a collar port in a lower position. In the lower position, the sleeve...http://www.google.fr/patents/US4880058?utm_source=gb-gplus-shareBrevet US4880058 - Stage cementing valve
