Spectacle Blind
From Piping Designer
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Ring Spacer
Ring spacers are bored to the matching pipe ID and are the same thickness as the "single blind" that it replaces. When removing a "single blind", either the flange and associated piping must be pulled together to seal the line, or a "ring spacer" must be installed to fill the gap. Thick single blinds or rigid piping systems normally require ring spacers.
Single/Line Blind or Blank
A positive shut-off device normally installed adjacent to, or in conjunction with, a valve. Their purpose is to prevent accidental flow through a pipeline to a vessel. With the exception of cast iron, plastic, or fiberglass services, they are not drilled with bolt holes, but fit inside the bolt circle of mating flanges. Pipeline blinds or blanks are not the same as bolting blind flanges. Single blinds ues standard gaskets.
A combination of a "single blind' and a "ring spacer" can be fabricated for field convenience as a single unit. Weight consideration and the associated difficulty of handling heavy pieces in the field are a primary consideration in specifying a "spectacle blind" or a combination of blinds. Spectacle blinds are meant to be rotated to change blind/spacer orientation.
Spectacle Blind
A spec blind is a combination of a ring spacer and single blind. They are usually permanently installed in a piping system and rotated as needed.
- Datasheet - ANSI Class 150, ANSI Class 300, ANSI Class 600, ANSI Class 900
Vapor Blind
Similar to a "single blind", but thinner, normally 1/8" (3mm) to 5/16" (8mm) thick. These are positive sealing devices intended to prevent accidental flow or leakage of vapors into a pipeline or vessel, usually while the system is in service. Vapor blinds are not to be subject to differential pressure.
Test Blanks
A test blank is specially designed blank used for hydrostatic or other incompressible fluid testing purposes only. Their advantage is cost and weight savings since higher allowable stress values (or lower safety factors) are used in their design.
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