cased wellbore a crossover tool secured to the lower end of the length of tubing a length of wash pipe secured to the lower end of the crossover tool a disc valve assembly secured to the wash pipe and positioned to a lower circulation position in the well bore a disc valve secured in a bore of the assembly in the upper portion of the assembly for shearing off the connection between the wash pipe and the disc valve assembly when the disc valve assembly is in an upper position providing to prevent fluid from flowing into the formation below the disc valve and to prevent production flow to the surface and a to rupture the disc valve at a predetermined time so that the production within the formation is allowed to flow through the assembly bore to the surface application_number US 1643393 A description the apparatus of the present invention referred to as a travelling disc valve is illustrated in the figures by the numeral 10 as best seen in the drawings the entire assembly housing the travelling disc valve assembly during lower circulation is shown in fig1 a through 1g the upper section of the assembly is illustrated in fig1 a through 1d and the lower section of the.