Abstract: An automatic bleed valve for bleeding air from a pressurized liquid reservoir or, with reversal of principal elements, bleeding liquid from a compressed gas reservoir comprises a piston in a piston chamber located in a flow passage leading from the reservoir. A capillary passage is provided through the piston, and the piston is urged upstream by a resilient spring. An orifice is located in the fluid channel. A sealing element is provided at the downstream end of the piston chamber. Upon activation of the hydraulic system while air is being expelled from the reservoir, the resilient spring will retain the piston in the upstream position, allowing gas to be bled from the reservoir through the fluid passage in the piston. When liquid begins to flow from the reservoir, the pressure differential over the piston increases, causing the piston to move against the downstream end of the piston chamber and seal off the fluid channel and the hydraulic reservoir.