Abstract: A gate valve has a pair of spaced-apart body halves with a slot positioned between them. The slot extends transverse, preferably perpendicular, to a fluid passageway. In one embodiment, an O-port gate is moveable within the slot and includes a pair of opposed major surfaces. The O-port gate includes a fluid impermeable portion and an aperture. A pair of opposed, plastic interior plates face each other and contact the opposed major surfaces of the O-port gate, thereby forming a cavityless gate valve. The plastic interior plates, formed of high-density polyethylene (HDPE), for example, have a lubricity that prevents the gate from seizing to them.