A fill valve for controlling the filling of a fluid reservoir such as a cistern. The valve minimizes the time needed to fill the reservoir by maintaining maximum fluid flow through the valve until instantaneous shut off of the fill valve once the reservoir is filled. The fill valve includes a reciprocating valve head carried on a valve stem connected to a float arm for determining the fluid level within the reservoir. The valve head is disposed within an enclosure having grooves for conducting fluid flow past the valve head to create a back pressure behind the valve head. The valve stem seals a passageway through the valve head which operates as a pilot valve during opening and closing of the valve.