Spectacle Blinds: Flow Control and Assurance Made Simple
A brief look at spectacle blind usage and critical considerations when choosing spectacle blinds for your piping system
Blinds and spacers offer an effective way to block flow to piping systems to prevent contamination, ease maintenance, or control flows.
Spectacle Blinds combine these two popular components to create a single solution for your routing and flow control needs -- particularly where positive shutoff is required.
Like with other piping components, choosing the proper spectacle blind is essential to reliable, long-term performance. The following considerations offer a solid foundation for determining the best option for your needs.
What is a Spectacle Blind?
To understand the benefits of spectacle blinds -- and some of their limitations -- it’s important to look at how they are designed.
They are a combination of a paddle blank (also known as a spade or slip blind) and a paddle spacer (also known as a spacer ring). One surface provides total closure for the piping systems while the other includes a ring that matches the inside diameter of the connected piping.
Instead of using a handle, web, or tie bar on each round, they are connected using a small nose piece or tie bar.
The final result looks like a figure eight or similar to the component’s namesake -- a pair of spectacles.
This design allows for complete closure or full operation of a piping system by rotating the spectacle blind as needed.
Spectacle Blind Installation
In most cases, spectacle blinds are installed for long-term use. Their simple operation and durable design ensure a long service life with minimal maintenance.
Spectacle blinds install between two horizontal pipe runs. Instead of bolting the blind in place around the full circumference of the pipe like you would a pipe flange, you instead install it by inserting one of the flange bolts through the hole on the central tie bar. The connection is then further reinforced by using gaskets between the flanges and spectacle blind.
This makes it critical to consider spectacle blind implementation in the design stage of your piping processes.
The additional space between pipe flanges will also require extended stud bolts to ensure a reliable, long-lasting fit.
Spectacle blinds are available in multiple face types to suit virtually any planned implementation, including:
- Female ring-joint blanks
- Male ring-joint blanks
- Raised face blanks
- Flat face blanks
Be sure to consider how this will impact gasket and flange requirements prior to installation.
Common locations for spectacle blind installation include:
- In bypass lines
- At inlets and outlets of rotary or static equipment
- At inlets and outlets of storage and processing vessels
Typical Uses for Spectacle Blinds
Spectacle blinds provide added flexibility during maintenance and system operations. They’re also an excellent option to ensure positive shutoff in the event of valve degradation and failure or operator error.
Adjusting spectacle blinds is straightforward. Simply loosen the bolts around the flange leaving the bolt running through the spectacle blind in place, rotate the desired face into the space between the pipes, and tighten the flange bolts again, some piping applications will require new gaskets to be installed.
Spectacle Blind Limitations
While spectacle blinds offer convenience over standalone slip and spacer blinds, there is one major drawback -- weight.
This is more evident in large or complex piping systems where the weight of multiple blinds could quickly add unacceptable stresses to the overall design.
In these cases, the standalone options are typically recommended to help avoid excess load.
As such, usage is typically limited to spectacle blinds up to 16-inches although the ASME B16.48 standard covers spectacle blinds up to 24-inches.
But it is important to remember that diameter isn’t the only weight concern. You’ll also need to consider the ANSI/ASME classification as well. For example, a 2500# spectacle blind will have a lower max diameter than a 900# spectacle blind due to its overall dimensions.
Unified Alloys stocks a full range of 304L-316L stainless steel spectacle blinds with other designs, thicknesses, and alloys available upon request. With more than 40 years as a leading stainless steel supplier in Western Canada and North America, Unified Alloys understands the needs of a range of industries. Contact us today and our expert sales analysts can help you find a solution for your next piping or processing system.