The present invention relates to a double-lifting system. The system of the invention which is used for reducing friction in the moving period of valve comprises the following components: a flow distributor; a valve seat; a driver which is relevant with the flow distributor and is used for moving the flow distributor from a first fixed position to a second fixed position; a compressed gas source which is communicated with the fluid of fluid distributor; a first regulator which is used for supplying the compressed air to the air distributor with a first pressure which is enough for sealing theflow distributor relatively to the valve seat when the flow distributor is at a first fixed position or a second fixed position; and a second regulator which is used for supplying the compressed air to the air distributor with a second pressure lower than the first pressure when the flow distributor moves between the first fixed position and the second fixed position.