Spectacle Blind

[Sachinkathe]

What is the exact use of Spectacle Blind?
Some times it is used with valves as spectcle blind gives same effect as that of isolation valves then why Spectacle blind is used? If the Spectacle blind is to be closed from open condition is there any spilage of the fluid ( in absence of Valve)?

Sachin

 

[BigInch]

Typically for maintenance purposes, or semi-permanent, yet still somewhat easily reconfigurable segments of piping that would be used alternatively over longer periods of time.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[zdas04]

Another way of saying what BigInch said is when a section of pipe has two mutually-exclusive functions, then a Spec blind can be used to give a clear visual indication of which function is being used. I've used them on compressor skids where the machine is a 2/3 stage and to change from one configuration to the other you rotate a set of spec blinds--that way anyone with the sense to pound sand can tell if the machine is 2 stage or 3 stage.

I see a lot of people using them for maintenance isolation and I think that is a horrible waste of money. You can accomplish the same thing by breaking the flange and inserting a skillet blind--spec blinds are expensive.

Yes, you will always spill a bit when you rotate them. Cost of doing business.

David

 

[cheute79]

spectacle blinds are expensive for maintenance isolation, but if you have an on-going need for the isolation, 1) you know it's always there, and 2) if you have to replace the skillet blind 5 or 6 times because it got misplaced or misused, it starts looking reasonable. You can always see it, and know exactly it's position. Good training and discipline with skillet blinds are probably the best way to go, if you can.

 

[Sachinkathe]

Ok cost business is one thing but it is used in hydrocarbon service also which is most dangerous thing so why not to stop at valve only (e.g. aircoolers isolations)

Sachin

 

[zdas04]

The term in "Positive Isolation" which is required when you are doing hot work. The methods of positive isolation are: (1) disconnecting and misaligning pipe; (2) blind flange; or (3) double block and bleed (two block valves with a vent between them, not allowed for some specific categories of hot work).

David

 

[cheute79]

two reasons: 1) a valve is not a positive shut-off (a seal could fail, for instance, or be bumped and then crack open, or it could have some debris built up on a sealing surface), 2) looking at a valve you can't assure yourself that it is completely closed and isolated. There have been many safety incidents and even deaths that have resulted because a line was not positively isolated with a blind.

 

[Sachinkathe]

In a nut shell it is required for following purposes
1) With valve for double chk of isolation while doing maintenance
2) To cover up the mallfunction of the valve if any
3) To have mental satisfaction that even if by mistake some one opens the valve then the area should not get fluded.
4) Its a better choice than plain blind as it may get misplace at time when it is required

Thanks a lot

Sachin