Abstract: An orifice valve having a moveable gate to control the flow of solids in a closed conveying system. The invention encompasses a valve housing with two complementary valve sections, each of a unitary construction. A single plate has a first planar surface, two opposed sidewalls and an end wall. The sidewalls include an integral flange section which presents planar surfaces that are placed in facing relationship with the planar flange surfaces of a second housing member so that the two form a closed cavity. A blade is received in the cavity and is reciprocal between open and closed positions so as to accommodate the flow of material or to block the flow.