Class 300 Spectacle Blinds

Class 300 Spectacle Blinds provide positive isolation for medium-pressure piping systems. The blind disc thickness increases compared to Class 150 to withstand the higher differential pressure across the closed blind. The spacer ring thickness remains the same as the blind disc to maintain consistent face-to-face dimensions when switching between positions.

These spectacle blinds are critical safety components in process plants where equipment must be isolated for maintenance, inspection, or emergency shutdown. The blind disc must be designed to withstand the full system design pressure with an appropriate safety factor, and material selection must match the piping specification for corrosion resistance and temperature capability.

Class 300 spectacle blinds are frequently specified at unit battery limits, around fired heaters, and at the inlet and outlet of major process equipment. Proper gasket selection on both sides of the spectacle blind is essential, as the sealing surfaces experience the full line pressure in the blinded condition.