Abstract: A valve including a fluid port; a valve seat round the port; and closure means movable towards and away from the seat, the closure means including a sealing surface engageable with the seat and a protrusion which extends from the sealing surface towards the seat, the protrusion being operative to create an accelerated flow of fluid between the seat and the sealing surface prior to the latter engaging the seat upon movement of the closure means towards the seat and the protrusion further being adapted for at least part thereof to be urged into sealing engagement with the surround of the port by pressure in the valve when the sealing surface engages the seat.