Abstract: A rotatable hydraulic damper includes a tubular fixed member and a shaft has a section rotatably received in the fixed member. A sleeve is rotatably engaged with the inner periphery of the fixed member and mounted to the section of the shaft. A passage is defined longitudinally through the shaft and a cap is mounted to the section of the shaft and seals the open end of the fixed member. Two chambers are respectively defined in the fixed member and separated by the sleeve. A plurality of longitudinal grooves are defined in an inside of the sleeve and an end of the sleeve is sealed by a bead urged by a spring. The hydraulic oil in the two chambers flows through the sleeve at different speeds so that the pivotable object closes slower than it is opened.

Abstract: A hydraulic hinge includes a cylinder sealed at both ends having a hexagonal shaft rotatably received therein with a portion thereof extending out of the cylinder. A circumferential space is defined between the shaft and the inside diameter of the cylinder to be filled with hydraulic fluid. A plug having a hexagonal hole corresponding to the cross section of the shaft is fit over the shaft to be rotatable therewith. The plug has an external thread of a desirable pitch to be engageable with an inner thread formed inside the cylinder so that the plug is linearly moved relative to the cylinder and the shaft by the pitch of the external thread thereof when the shaft is rotated. The plug divides the circumferential space into two chambers. A passage is formed in the shaft to form a fluid communication between the two chambers. A spherical member is spring-biased to block the passage, serving as a check valve, so as to allow the hydraulic fluid to flow uni-directionally at a normal flow rate.