Class 150 Spectacle Blinds

Class 150 Spectacle Blinds are the most commonly used figure-8 isolation devices in process piping. They are installed between standard Class 150 raised face flanges, with the blind disc or spacer ring seated on the gasket surface. The outside diameter of each disc matches the gasket OD for the corresponding pipe size.

At Class 150, the blind disc thickness is relatively thin, making these spectacle blinds lightweight and easy to rotate during line-opening procedures. Standard sizes range from NPS 1/2 through NPS 24, covering the vast majority of process and utility piping isolation requirements in refineries, chemical plants, and power stations.

Installation requires sufficient flange separation to rotate the spectacle blind, which is typically provided by spacer rings or by designing the piping with enough flexibility to spread the flanges. A handle or lug extending beyond the pipe insulation indicates which disc is in the flow path, providing a visible indication of the isolation status.