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.

Abstract: A knife gate valve wherein the seat for sealing against the knife gate is provided on a separate removable/replaceable carrier portion mounted to the body of the valve. The seat may be a metal rim for metal-to-metal sealing or it may carry a resilient seal. Removable, seat carrying carriers can be provided on both sides of the knife gate for bi-directional control of the slurry flow. The seats may include seals that are sandwiched between the body and the carriers to insure against dislodgement. The seals may include a two-part seal with a non-exposed resilient seal that is urged by a resilient O-ring into bubble tight sealing against the knife gate.