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NFPA 68 Pstat, Pred, and Pes relationships

NFPA 68 Pstat, Pred, and Pes relationships

NFPA 68 Pstat, Pred, and Pes relationships

(OP)
I am working on some venting projects for some baghouses and conveyors. We have a given vent test pressure (Pstat = 1.5psi). We need to determine the vent area and verify the enclosure strength is adequate. In reviewing the NFPA 68-2007 requirements for Pred and Pes, I have the following questions/thoughts:

1. For a high pressure enclosure (>1.5psi) is there a minimum value or factor that Pred must be greater than Pstat (the vent static activation pressure)? Based on Annex A section A.6.3.2, I am thinking that Pred can be set to equal 1.5*Pstat.

2. Equation 6.3.2 defines Pred < Pes/DLF, and DLF = 1.5 so Pes(min) = 1.5*Pred. If my interpretation in question 1 is correct and substituting in Pes 1.5*1.5*P.stat . Is this correct?

3. If 1 and 2 are all wrong, how do you define the value of Pred?

4. Is 6.3.1.2 and 6.3.2 saying the same thing or how do these two provisions work together?

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