A variable wash flow filter assembly comprising: a housing which defines an inlet along a longitudinal axis, at least one filtered flow port, and at least one thru flow port; a wash filter within said housing adjacent to said at least one filtered flow port; a wash velocity control cone biased within said housing by a bias member positioned in an internal space in the cone, said wash velocity control cone being movable between a minimal position and a maximum position relative to said wash filter with a conical gap between the wash velocity cone and the wash filter, the variable wash flow filter assembly arranged to split a fuel flow through said inlet between a burn flow through said thru flow port and a filtered flow through said filtered flow port; and a guide with a spring seat to react said bias member, said guide being operable to guide said wash velocity control cone along said longitudinal axis between said minimal and said maximum position; characterised by: the guide having a sleeve section which extends around the outside of the wash velocity control cone; and at least one activation deltaP window, which is located through the sleeve section downstream of the conical gap and which in part, controls movement of the wash velocity cone by avoiding the potential closing force caused by relatively high velocity fluid which results in a drop in static pressure, wherein when the wash velocity control cone is in the minimal position the activation deltaP window is open to provide a path between the at least one thru flow port and the internal space of the wash velocity control cone and a path between the conical gap and the internal space of the wash velocity control cone, and wherein when the wash velocity control cone is in the maximum position the activation deltaP window is closed to shut the path between the at least one thru flow port and the internal space of the wash velocity control cone. a housing which defines an inlet along a longitudinal axis, at least one filtered flow port, and at least one thru flow port; a wash filter within said housing adjacent to said at least one filtered flow port; a wash velocity control cone biased within said housing by a bias member positioned in an internal space in the cone, said wash velocity control cone being movable between a minimal position and a maximum position relative to said wash filter with a conical gap between the wash velocity cone and the wash filter, the variable wash flow filter assembly arranged to split a fuel flow through said inlet between a burn flow through said thru flow port and a filtered flow through said filtered flow port; and a guide with a spring seat to react said bias member, said guide being operable to guide said wash velocity control cone along said longitudinal axis between said minimal and said maximum position; characterised by: the guide having a sleeve section which extends around the outside of the wash velocity control cone; and at least one activation deltaP window, which is located through the sleeve section downstream of the conical gap and which in part, controls movement of the wash velocity cone by avoiding the potential closing force caused by relatively high velocity fluid which results in a drop in static pressure, wherein when the wash velocity control cone is in the minimal position the activation deltaP window is open to provide a path between the at least one thru flow port and the internal space of the wash velocity control cone and a path between the conical gap and the internal space of the wash velocity control cone, and wherein when the wash velocity control cone is in the maximum position the activation deltaP window is closed to shut the path between the at least one thru flow port and the internal space of the wash velocity control cone. the guide having a sleeve section which extends around the outside of the wash velocity control cone; and at least one activation deltaP window, which is located through the sleeve section downstream of the conical gap and which in part, controls movement of the wash velocity cone by avoiding the potential closing force caused by relatively high velocity fluid which results in a drop in static pressure, wherein when the wash velocity control cone is in the minimal position the activation deltaP window is open to provide a path between the at least one thru flow port and the internal space of the wash velocity control cone and a path between the conical gap and the internal space of the wash velocity control cone, and wherein when the wash velocity control cone is in the maximum position the activation deltaP window is closed to shut the path between the at least one thru flow port and the internal space of the wash velocity control cone.