Spectacle Blind is a steel plate cut into two discs of a certain thickness.
The two discs are attached to each other by a section of steel similar to the nose piece of a pair of glasses. One of the discs is a solid plate, and the other is a ring whose inside diameter is equal to that of a flange.
1. Spectacle blind 2. Flanges 3. Gaskets 4. Stud Bolts
1. Spectacle Blinds are applied in pipe systems, which regularly need to be separated from other installations. Generally, a Spectacle Blind is mounted in the “open” position so that flow through the pipe is possible. If the Spectacle Blind in the “close” position is rotated, the pipe is blanked off and no flow is possible.
2. Maintenance on a pipe system can be a reason to rotate the spectacle in the “close” position. This run will take place through the hole, that is drilled in the connection piece. By loosening of all bolts, and partial removal of them, the Spectacle Blind can be rotated. After replacing the gaskets (new gaskets are to recommend), the bolts can be re-assembled and tightened.
3. The Connection piece is engraved/marked with the diameter and the Pressure Class.
Spades and Ring Spacers are basically the same as Spectacle Blinds, except that both are not attached to each other.
Spades and Spacers should be applied in systems where maintenance is often not necessary, or in applications with large pipe sizes to prevent unnecessary weight to a flange connection. Spades and Spacers usually will be chosen over a Spectacle Blind, as 2 separate parts.
Maintenance on a pipe system can be a reason to temporarily replace a Ring Spacer for a Spade. By loosening off all bolts, and half of the bolts temporarily removed, the Spade or Spacer can be placed. After replacing the gaskets (new gaskets are to recommend), the bolts can be re-assembled and tightened.
The handles are often specially marked, or both have a different design. The handle, the diameter and the Pressure Class of a Spade or Spacer is engraved.
The sealing surfaces of a Spectacle Blind, Spade or Ring Spacer are usually in accordance with the Face Finish of the flanges. The diameter is slightly larger than the Raised Face of a flange; The bolt diameters are dependent on the flange size. The thickness is from the Pressure Class of a flange.
ASME B16.48 covers pressure-temperature ratings, materials, dimensions, dimensional tolerances, marking, and testing for operating line blanks in sizes NPS ½” (15mm) – NPS 24” (600mm) for installation between ASME B16.5 flanges 150#, 300#, 600#, 900#, 1500#, and 2500# Pressure Classes.
Spectacle Blinds, Spades and Ring Spacers should be made from a plate or forging specification, approved for use by ASME B31.3, of essentially the same chemical composition as the mating flanges and piping involved.
Note: always try to apply spacer thicknesses in accordance with ASME B16.5.