Abstract: The invention provides a valve having a plunger which is moveable towards and away from an annular seat surrounding an inlet port, the seat has, immediately adjacent and surrounding the port, an upstanding annular rim and, immediately surrounding said rim, a flat annular seating surface. The plunger has a nose constituted in part by a flat annular metal portion adpated to be brought into metal-to-metal contact with the flat annular seating surface on the valve seat. On the nose of the plunger immediately within said flat annular metal portion there is formed a recess in which is housed a sealing ring of elastomeric material. When the flat annular portion of the plunger nose is in metal-to-metal contact with the flat annular seating surface of the valve seat, the raised rim of the valve seat enters or is entered into the mouth of the recess and is pressed into resiliently deforming contact with the part of the elastomeric sealing ring which occupies the recess, thus obtaining sealing obturation of the port.