Fluid operable valves

Claim 1

A fluid-operable valve including a body, a cavity within the body, an inlet means in the body and leading to the cavity, an outlet means in the body and communicating with the cavity, a first valve seat associated with the inlet means, a second valve seat associated with the inlet means and positioned downstream of the first valve seat, a pilot valve member co-operable with the first valve seat and adapted for actuation into or out of contact therewith, a main valve member co-operable with the second valve seat and fluid operable into or out of sealing contact therewith, the main valve member having a sealing face, and purge means directed towards the sealing face of the main valve member when, in use, the main valve member is in close adjacency to the second valve seat for a brief period after the pilot valve member contacts said first valve seat for purging of the sealing face of the main valve member, in which a cylinder mounting block is disposed within a part of the cavity of the valve body, a cylinder is formed in the cylinder mounting block, a stem is provided for the main valve member and a piston is carried on the stem and is reciprocable within the cylinder, the cylinder is sealed from the cavity and the cylinder mounting block is provided with ports for the introduction and exhaust of fluid to and from each side of the piston, the stem is provided with an axial bore, a further coaxial cylinder is formed within the cylinder mounting block in which a rod of the pilot valve member is slidable co-axially within the axial bore of the stem of the main valve member and within the further cylinder.