Abstract: A flow switch includes a movable shuttle enclosed within a bore having narrower and wider bore sections. The shuttle has a solid cylindrical portion and a vaned portion. When there is no fluid flow from the inlet to the outlet, the shuttle rests on a part-conical portion of the bore. When fluid pressure is applied at the inlet, the shuttle is raised until the vaned portion is partly within the wider bore section. Fluid can then flow through the spaces between the vanes in the vaned portion, and fluid flow is detected by the change in position of the shuttle. The shuttle can be made magnetic, whereupon a magnetic sensing means such as a magnetic reed switch can be used to detect fluid flow. This arrangement has the advantage that resistance to flow and pressure drop are minimal compared to previous designs.