A valve assembly 2 for controlling the supply of water an irrigation system comprises a main body 4 having a platform 12 bordered by downwardly extending side walls 8. A float 16, located below the platform, is moveable towards and away from the platform by water in the main body. An arm 18 is pivotally connected to the float and engages with a tube 30 extending from a water inlet 14 enabling water to flow through the tube and the valve assembly when unrestricted. The arrangement is such that raising the float by water causes the arm to rise to the underside of the platform to produce a restriction (32 figure 3) in the tube to stop the flow of water to the assembly, and lowering the float causes the arm to lower to remove the restriction and to allow water to flow through the valve assembly. Magnets 20, 22 may be positioned on the arm and underside of the platform.
