Abstract: A fluid flow control valve comprising an outer casing with an inner valve member displaceable between first and second positions within the casing, the valve member including passages which interconnect different valve inlets and outlets dependent on whether the valve member is in its first or second position, the valve member being made from plastic material so that the diameter of the valve member can be increased without increasing its weight above that of a conventional metal inner valve member. This allows the passages through the inner valve member to be of the same internal diameter as the tubing leading up to and away from the valve. The valve member can be acted upon by a magnetic restoring means which tends to return the valve member towards its first position when displaced therefrom.