Abstract: A dump valve apparatus is described which may be used to drain a chemical reactor tank. The valve includes a valve seat ring having a substantially vertical inner seat surface defining a discharge passage, a valve plug having a substantially vertical outer side surface which fits in the seat ring and a seal formed between such vertical sealing surfaces. The valve inlet and outlet openings are aligned with the vertical discharge passage through the seat ring and the sealing surfaces are vertical to minimize the amount of material deposited thereon. The outer plug side surface slides across the inner seat surface during opening and closing of the valve so that such surfaces wipe each other to remove deposited material and provide a self-cleaning valve. The inner seat surface is provided with a plurality of annular grooves containing elastic sealing members which engage the outer plug side surface to form a liquid tight seal which is resistant to the pressure created by the liquid within the tank.