HYDRAULIC STEPPING VALVE ACTUATED SLIDING SLEEVE

摘要

A fluid actuator for displacing a predetermined volume of fluid comprising: a piston disposed within a cylinder for displacement of a predetermined fluid volume by translation from one end of the cylinder toward an opposite end; a force bia s of said piston toward the one cylinder end; a fluid supply to the one cylinder end; a first pressure differentially closed piston by-pass conduit whereby the conduit is closed b y a fluid pressure in the cylinder one end that is sufficient to displace the piston against said force bias; and a second pressure differentially closed piston by-pass conduit for permitting a fluid flow from the opposite cylinder end toward said one end, the second by - pass conduit being disposed through said piston.