Spectacle Blinds, Fig 8 Blinds

A Spectacle Blind is essentially a simplistic valve which fits in the line between two flanges and is bolted in place. One side of the Spectacle Blind is open (spacer) and the other side of the Spectacle Blind is blanked (blind or spade).

To change it from open to closed, all except the pivot bolt are removed and the Spectacle Blind is rotated on its centre hole so the blind side is in between the flanges. The bolts are then installed and tightened. The side that protrudes out of the pipe is a clear indicator of whether the pipe is open or closed.

It is used usually for maintenance when it is required to isolate a section of pipe or isolate a device. Because this is a semi-permanent isolation it is very safe and safety is often the mentality behind the use of a Spectacle Blind in maintenance operations. They are cheap and robust compared to a valve. 

Spectacle Blind Stamping

Typically a Spectacle Blind will have stamping showing its size, rating, standard, material, heat number, Balcombe Engineering stamp and production traceability code.   Many clients ask to have their own part identification and process traceability stamped on the Spectacle Blind.

Spectacle Blind Standards

A range of international standards and specific custom drawings dictates the specifications around Spectacle Blinds.  The most common standard is ASME B16.48 which provides dimensions to suit ASME B16.5 flanges.  

Spectacle Blinds Sealing Facings

Depending on the application requirement, Spectacle Blinds are usually produced as a flat face, raised face or ring joint sealing surface. The spiral sealing face is a specified finish typically Ra 3.2µm-6.3µm.

Spectacle Blind Materials

Being an Australian manufacturer, Balcombe Engineering are able to manufacture the Spectacle Blinds in a material with the testing in line with the client specification. Typically, Spectacle Blinds will be manufactured from carbon or stainless steels. Typical carbon steel materials are AS1548 460NR, A516 Gr70 or forgings like A105, A350 LF2, A350 LF3. Corrosion resistant materials A240 P316L, A240 P304L, UNS31803 are common. Less common but easily supplied are Super Duplex 2205 and Incoloy 625.

Additionally, specialist finishes are available, for example - galvanising, PTFE coatings and linings and various epoxy finishes.

Corrosion Protection and Packaging

A Spectacle Blind will always have 4 sealing faces that requires significant sealing face protection.

Whether you want the Spectacle Blind protected for 2 weeks or 2 years Balcombe Engineering have a packing system that ensures that Spectacle Blinds arrive at the installation in good condition.  Our sales team are happy to provide additional information if more robust corrosion protection is required.

Special Spectacle Blinds

This photo shows a fully milled Spectacle Blind
produced from an ingot of an exotic material.

Sometimes a specific engineering requirement may dictate the need for special material and construction required to produce the Spectacle Blind. Balcombe Engineering are a manufacturer with full ISO 9001 certification and are able to produce to your requirements including detailed testing and documentation.  All material is traced through the Balcombe Engineering system and ITPs and MDRs are available on request. Your order can be packaged in line with your engineering or project specifications and we are set up to complete the tasks within remarkably short delivery time frames.

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