Abstract: The steam valve includes a fast-acting control valve and stop valve acting against a valve seat in a steam flow passage in a closed position. An outlet passage below the valve seat has transition walls therebetween, affording a smooth, continuous flow past the seat into an outlet whereby head losses are reduced. An annular screen about the valve has support structure recessed in the walls of the inlet to reduce flow blockage and vortex formation. A balance chamber disposed above the control valve has a bleed hole for equalizing steam pressure in the balance chamber and steam valve which inhibits depressurization of the balance chamber and facilitates fast closing of the control valve. Buttress threads interconnect the control valve stem and the control valve head to preclude binding of those parts due to oxide buildup.