What Are Figure-8 Blanks?
Figure-8 blanks, also known as spectacle blinds or paddle blinds, are two-part devices shaped like the figure 8: one side is a solid blind, the other is a spacer (ring). They are installed between flanges to temporarily or permanently isolate a section of the pipeline for maintenance, testing, or modification. When the blind is rotated to the solid side, flow is completely blocked; when rotated to the ring side, flow passes through.
Unlike other isolation methods (e.g., valves), figure-8 blanks provide positive mechanical isolation with no risk of leakage through a worn seat. This makes them critical for safety in oil & gas, chemical, petrochemical, and power generation systems.
Impact on Pipeline Safety
Properly selected and installed figure-8 blanks prevent accidental release of hazardous fluids, protect maintenance personnel, and avoid cross-contamination. The key safety factors include:
- Positive isolation: The solid blind physically blocks the line, eliminating reliance on valve seals.
- Visual verification: The position (blind or spacer) is immediately visible, reducing human error.
- Pressure containment: They must withstand maximum design pressure and any thermal cycles.
