Abstract: An improved, modular, internally shifting, double acting linear fluid actuator system which is adapted to be driven by liquid, air stream, steam, or gas, (collectively referenced as fluid medium.) The present invention is comprised of three core modules and two attachment mechanisms: a Control Module, two Canister Modules, and Canister Adjustment Plates. The Control Module receives pressurized fluid medium, internally shifts the fluid medium flow into and out of Canister Modules, and exhausts depressurized fluid medium. The Canister Modules perform the work for each actuator application, and are attached to the Control Module by Canister Adjustment Plates at each end of the Control Module, which allows attachment to different diameter canister modules simultaneously. The Canister Modules may operate at different pressures, different volumes, or perform different applications simultaneously.