A ball valve includes a valve element and a single piece packing that seals the valve element within a valve cavity. The single piece packing is installed over the valve element at room temperature or may be molded thereon. The valve element may include a flow control element such as a ball and upper and lower trunnions. The various dimensions of the valve element and packing are selected to facilitate room temperature assembly and to substantially reduce the volume of packing material, thereby improving the performance of the valve over wider temperature ranges and pressure ratings.