Patent ID: 8622131

Claim:
A system for launching cementing plugs in a subterranean well, comprising: i. a first portion, comprising (a) a plug basket that is movable and initially contains at least one bottom plug and a top plug; (b) a dart catcher that contains a hydraulic-liquid reservoir and a piston that forms a hydraulic seal in the reservoir; (c) a hydraulic liquid inside the reservoir that is in hydraulic communication with the plug basket; (d) a first tubular body through which the hydraulic liquid flows; (e) an expandable fluid chamber into which hydraulic liquid may flow upon displacement through the first tubular body, thereby forcing the movable plug basket to move upward and expel the plug; and (f) a second tubular body comprising ports through which wellbore-service fluids may flow; ii. a second portion, comprising at least one bottom dart; and iii. a third portion, comprising a top dart; wherein, upon the arrival and subsequent axial movement of the bottom dart within the dart catcher, the hydraulic liquid is displaced by the piston to a sufficient extent to cause the expulsion of the bottom plug from the system; wherein, upon the arrival and subsequent axial movement of the top dart within the dart catcher, the hydraulic liquid is displaced by the piston to a sufficient extent to cause the expulsion of the top plug from the system.