Abstract: A minimum drag fluid reaction element including a rotatable shaft adapted to be supported by a vessel carried upon or within a fluid medium; and a rigid fluid reaction fin fixedly attached to the shaft for extension into the fluid medium, the shaft and the fin extending in opposite directions from a common intersection and forming an angle other than a right angle therebetween; the axis of rotation of the shaft lying in a plane generally normal to the fin whereby rotation of the shaft moves the fin through a path describing a right conical section. The angle between the fin and the shaft is preferably obtuse and the plane containing the axis of rotation of the shaft peripherally bisects the fin.

Abstract: The invention provides an unbalanced, butterfly check valve including a hollow main body member having a frusto-conical valve seat disposed interiorly therein, and a valve closure member in the form of a generally circular plate having a frusto-conical periphery conforming to the valve seat; the valve closure member is disposed for pivotal movement about an axis normal to the axis of the main body member and laterally offset from the center thereof. The center of gravity of the valve closure member biases the same to the closed position and is located such that the torque required to open the valve decreases as the closure member moves from its closed position to its open position. The closure member may be also fluid-dynamically profiled so as to remain open in response to a minimum flow condition and to rapidly become closed upon the occurrence in a change in flow direction.