Abstract: A cylinder valve comprising a hollow cylinder having a cross-passage, for use as a valve element, preferably in high temperature fluid solid service, to block flow. The cylinder is enclosed in a refractory lined steel body which includes a main flow passage. The valve cylinder can be rotated 90.degree. about its longitudinal axis to either fully open or fully close the flow passage in the extreme cases. It can also function in an intermediate position as a throttling member. Water or other coolant flow may be provided and maintained through the cylinder if hollow, or the cylinder can be solid for small size valves. The refractory in the main flow passage surrounding the cylinder serves the dual purpose of valve seat and as insulation against extreme temperatures.