What Is a Figure-8 Blind?
A figure-8 blind (also called spectacle blind or 8字盲板 in Chinese standards) is a piping isolation device consisting of a solid plate (blind) and a ring (spacer) connected in a figure-8 shape. It allows quick conversion between open and closed positions by rotating the assembly. Unlike a simple blind flange, the spectacle blind provides a permanent, leak-tight closure without removing the fitting from the line.
Applications in Industrial Piping
Figure-8 blinds are used when a positive isolation is required during maintenance, testing, or temporary shutdown. Common applications include:
- Refineries and petrochemical plants: isolating equipment like heat exchangers, pumps, and compressors.
- Pipelines: providing a visible break for safety during pigging or hydrotesting.
- Chemical processing: preventing cross-contamination between process streams.
- Utility systems: separating steam, water, or gas lines for repair.
