Abstract: A valve comprises a first relatively fixed valve component assembly surrounding a second valve component assembly which is relatively movable within said first assembly. A seal is provided between the first and second valve component assemblies and a barrier assembly is provided for preventing particulate contaminant material reaching the seal. The barrier assembly comprises first and second barrier elements extending around said second valve component assembly. The first barrier element or elements are in engagement with the first valve component assembly and the second barrier element or elements are in engagement with the second valve component assembly. The barrier elements may be spring rings and form a labyrinth type seal between the two valve component assemblies.