1 reply to this topic

[pleckner]

Helena:

First off, I invite you to read my series on rupture disks that is published in the Free Articles, Pressure Relief Design section of this website. It will help you tremendously in understanding how the rupture disk fits into the overall relief system either as a stand alone device or in combination with a relief valve.

Second, standards do not say anthing about pressure drop in a relief device tail pipe (discharge piping). They talk about constant and allowable variable back pressures and inlet pressure drops. You may either be referring to the allowable variable back pressure against a conventional relief valve (10% of set pressure) before they loose capacity and the ability to stay opened or you are referring to the over pressure allowed in the vessel during relief.

If you are indeed talking about variable back pressure, this is icaused by the built up back pressure when the system is in full relief and this built up back pressure is a function of pressure loss in the system but is not the only pressure you have to be concerned about. If the flow is choked (isothermal) or sonic (adiabatic), then you also have to be concerned about the critical or choked pressure as well.

Please provide more information and we can better address your concerns. Also, please read those articles I referenced. They will go a long way to help you undestand the system and may even help you answer the question I think you may be asking.