Abstract: A gate valve comprises a body member having a bore therethrough, a gate member movable transversely of the bore between an open position permitting full flow through the bore, and a closed position preventing flow through the bore, and a stem portion mounted in the body member to be axially fixed therein but rotatable relative thereto, one end of the stem portion co-operating with the gate member whereby rotation of the stem portion results in movement of the gate member between its open and closed positions, a sleeve member secured to, to be rotatable with, the stem portion external of the body member and defining an annular gap between the stem portion and the sleeve member, and an annular skirt within said gap, the skirt being rotatably fixed but axially movable relative to the stem portion, the skirt and sleeve member threadedly engaging one another such that rotation of the sleeve member results in axial movement of the skirt relative to the sleeve member and the stem portion in a direction dependent upo