4 replies to this topic

[raju333]

Hi
why two valves are required at battery limit.

[Dacs]

This is an example of a typical BL arrangement:



Let me give you this scenario. You've decided to isolate a certain area of a plant. Obviously you need to close all the lines going in and coming out of the area to be isolated.

See the spectacle blind? What's its purpose? How do you engage it from open to close without the valve arrangement?

Hope that answers your question

[JoeWong]

Other reason (but may not only applicable to BL) could be minimize hazard due to valve leakage.

Hi
why two valves are required at battery limit.

In an emergency you need to isolate your plant from the usually massive inventory in the pipeline beyond. The reliability of closure of a single valve is not really very high therefore 2 valves are often needed to achieve the required Probability of Failure on Demand (PFD) of the isolation function, i.e. to achieve the required Safety Integrity Level (see IEC 61511).

[Dacs]

Other reason (but may not only applicable to BL) could be minimize hazard due to valve leakage.

That's another scenario that I'm thinking, although this is not only limited to B/L.

And this is usually employed on high pressures or for mitigating valve leakage (maybe because of fluid toxicity).

Although this is just plain guesswork for us since the OP did not elaborate further on the configuration of the double valve he/she's asking.