A continuously variable turbine includes a case assembly with a case body defining a chamber, a rotor assembly positioned in the chamber, and a pair of valve assemblies. The rotor assembly includes a ring piston and a rotor body positioned within the ring piston. The rotor body is connected to a shaft, and the rotor body rotates concentrically about an axis extending through the shaft while the ring piston rotates eccentrically about the axis. Each valve assembly is positioned outside of the ring piston relative to the rotor assembly and includes a valve body and a seal component attached to the valve body. Each seal component has a surface with a curvature that matches the outer curvature of the ring piston to form a continuous surface seal between the seal component and the ring piston as the ring piston rotates eccentrically about the axis. The position of the continuous surface seals in the chamber defining a first sub-chamber and a second sub-chamber between the surface seals. The case body includes an intake port and an exhaust port for each sub-chamber.

A pneumatic engine includes first and second pneumatic motors. Each motor has a stator, a rotor, and a gas flow path. The rotor is rotatably connected to the stator. The gas flow path is defined at least in part by the stator and the rotor, and extends from a gas inlet to a terminal gas outlet. The gas flow path has an expansion portion extending between the gas inlet and an intermediate gas outlet, and a compression portion extending between the intermediate gas outlet and the terminal gas outlet. The terminal gas outlet of the first pneumatic motor is fluidly connected upstream of the gas inlet of the second pneumatic motor.

A hydraulic device can include two or more rings, a rotor having a plurality of vanes, and an adjuster. The two or more rings can be rotatably mounted within the hydraulic device and arranged adjacent one another configured for relative rotation with respect to one another. The rotor can be disposed for rotation about an axis within the two or more rings and can have a plurality of circumferentially spaced slots, each slot having at least one of the plurality of vanes located therein. The plurality of vanes can be configured to be movable between a retracted position and an extended position where the plurality of vanes work a hydraulic fluid introduced adjacent to the rotor. The adjuster can be configured to translate linearly to rotatably position the two or more rings relative to one another to increase or decrease a displacement of the hydraulic fluid between the rotor and the two or more rings.

The combined pump and energy recovery turbine includes at least one fluid flow pressurizing a sliding vane pump and a sliding vane energy recovery turbine that recovers energy from a second fluid flow, such as the brine discharge from an RO seawater desalination system. A cylindrical rotor has two sliding vanes in respective slots, the rotor being concentrically disposed within an oval-shaped enclosure defining two mirror image crescent-shaped chambers, each chamber having inlet and outlet passageways. The first chamber pressurizes the first fluid flow, and the second chamber functions as a second outflow-driven energy recovery turbine, thus enabling the single rotor device to operate as a pressurizing pump on the first fluid flow, and second outflow-driven energy recovery turbine recovering energy from the pressure drop in the second fluid flow.