<p>A float valve is mounted within the ullage of a liquid storage tank and is fitted to a lower end of a vapour vent line. The float valve includes a generally tubular vent body having an opening arrangement which allows vapour to escape from the tank into the vent line, and a float assembly which undergoes damped upward movement in response to the liquid level within the tank exceeding a threshold level. The float assembly comprises a sleeve and a float arrangement separated from each other by an adjustable distance. In this way, the volume of liquid required in the tank to make the float assembly move upward can be changed. The float valve may include a relief valve or a plug with a bleed orifice to permit vapour flow from the tank to the vapour vent line in the event that the pressure within the tank exceeds a predetermined value.</p>
