Abstract: A valve assembly of a trunnion type valve such as a ball valve in which a valve seat retainer having a valve seat at its one end is slidably received in a valve casing and a biasing means is provided between the other end of the valve seat retainer and an annular shoulder of the valve casing opposing the former. The biasing means is comprised of a ring and a plurality of spring elements which are kept in a circular arrangement by the connecting ring and each have a substantially U-shaped profile for biasing the two end surfaces of the valve casing and the valve seat retainer. Since the biasing means is simple and can be readily adapted to valves of different sizes, it offers a great advantage in use. Furthermore, the manufacture of the biasing means is simple and causes almost no material loss in the manufacturing process.