Abstract: A lower control system serves to regulate the flow rate of lifting jack oil, and is installed between a reverse flow valve and an inner oil chamber, regulates the oil flow from the inner chamber to an outer chamber. The lower control system comprises an outer valve body, a steel ball, a spring, and a throttle body. The throttle body has a tapered portion, formed at its front end, and at least one throttling slot way and one lateral slot way, formed respectively on the tapered portion and the circumferential wall thereof. When the jack is not loaded, a reverse flow valve can lift the steel ball so that oil swiftly flows by the throttle body through the lateral slot ways to complete the reverse flow. When the jack is loaded, oil gently flows by the throttle body through the throttling slot ways, leading to a reduction of oil flow rate and a slower descending of the jack.

Abstract: A lower control system serves to regulat the flow rate of lifting jack oil, and is installed between a reverse flow valve and an inner oil chamber, regulates the oil flow from the inner chamber to an outer chamber. The lower control system comprises an outer valve body, a steel ball, a spring, and a throttle body. The throttle body has a tapered portion, formed at its front end, and at least one throttling slot way and one lateral slot way, formed respectively on the tapered portion and the circumferential wall thereof. When the jack is not loaded, a reverse flow valve can lift the steel ball so that oil swiftly flows by the throttle body through the lateral slot ways to complete the reverse flow. When the jack is loaded, oil gently flows by the throttle body through the throttling slot ways, leading to a reduction of oil flow rate and a slower descending of the jack.

Abstract: An air valve assembly adapted for use in a hydraulic jack and constructed to include a valve block, the valve block having a threaded front neck for mounting, a longitudinal center through hole, and a radial air hole in communication between the longitudinal center through hole and the atmosphere, an air guide block mounted inside the valve block, the air guide block having a spiral groove around the periphery in communication between two distal ends of the longitudinal center through hole of the valve block, a stop plate fixedly mounted inside the valve block above the air guide block, the stop plate having a center round hole for the passing of fluid, and a felt element fixedly mounted inside the valve block and attached to the stop plate at the top and aimed at the radial through hole of the valve block to stop hydraulic oil from passing out of the center round hole of the stop plate and to let outside air pass from the radial through hole of the valve block through the center round hole of the stop plate