Abstract: A high-volume, high-pressure valve is provided for attachment to the water inlet of a firetruck to receive the downstream end of the main supply hose connected to the fire hydrant. The heavy construction necessary to withstand the high pressures and rapid flow rate of water includes a gate which slides over a dam plate, with both the gate and the dam having slotted apertures which alternatively align and misalign as the gate slides over the dam to alternately open and close the dam.