Abstract: The air release valve comprises a valve chamber (36) having an inlet (20) and an outlet (24). Inside the chamber is a control float (38) which is responsive to changes in liquid level in the chamber. There is also a a stack of valve members (40, 42, 44) in the chamber above the control float. The valve members have vent passages through them which increase in size with increasing height in the stack but which are smaller than the outlet (24). The top valve member (44) in the stack is designed to be lifted up, by differential air pressures acting on it, to seat on the outlet (24) and thereby reduce the effective size of the outlet when a pipeline served by the air release valve is filling with liquid and the liquid displaces air through the valve.