Abstract: Air bladder type vent valve is disclosed having an air bladder fastened to the air vent of the hydraulic oil tank of an enclosed hydraulic transmission system, for example, hydraulic jack and suspended inside the hydraulic oil tank, and a fastening device, which affixes the air bladder to the periphery of the air vent in an airtight status to keep the inside space of the air bladder in air communication with the atmosphere so that the inside pressure of the hydraulic oil tank is maintained in balance with the atmosphere during the operation of the enclosed hydraulic transmission system to pump hydraulic fluid in and out of the hydraulic oil tank.

Abstract: A. three-shift lifting mechanism includes a hydraulic device disposed at the front side of a valve block and adapted to lift a lifting tube to raise weights, the hydraulic device defining an oil accumulation chamber, a rapid-lifting oil chamber for rapid lifting of the lifting tube to the lifting position, and a high-pressure oil chamber for lifting the lifting tube to raise weights, a piston pump disposed at the back side of the valve block and defining a front working chamber and a rear buffer chamber, and oil passages so arranged that hydraulic oil can be supplied from the oil accumulation chamber and the rear buffer chamber to the front working chamber and then to the rapid-lifting oil chamber or the high-pressure oil chamber to lift the lifting tube.