Rotovalve is/was a registered trademark. The company that owning it used to make cone valves. Cone valves are similar to ball valves and plug valves but they are shaped like truncated cones rather than balls or cylinders. They are cone shaped so that they can lift as they turn which prevents wear on the seals while still making positive contact when shut. They can be used anywhere you'd use a ball valve or plug valve and are suitable for high pressure work.
Unless you mean a fixed cone valve aka Howell-Bunger valve. The end of the pipe has a cone, point facing into the pipe in the end of the pipewith a gap between the end of the pipe and the base of the cone.. This forces fluid exiting the pipe to leave as an anular discharge rather than single jet. The gap between the pipe and cone can be closed off with a sleeve that slide forward and back. Jet valves are similar but they have a hood or at the end of the pipe to discharge the fluid as a hollow jet. Both prevent a single "solid" jet of water forming and the hollow jet or hollow conical discharge slows down faster and causes less erosion.
Hydro dams may use a cone valve upstream of a fixed cone valve/ring jet valve as part of their floodgates.