In the event of an explosion through a high pressure gas pipe, is there a way to vent the pressure wave, in order to protect downstream objects? The mechanism must be faster than sound; pressure relief valves and even rupture discs are actually too slow and will not respond to such a "fast" pressure wave.
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$\begingroup$ would that also be because of the size of the resulting pressure wave? And, how big would the valve need to be? $\endgroup$– Solar MikeCommented Oct 27, 2017 at 16:03
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$\begingroup$ I think attenuating the pressure wave (spreading the spike over time) using something like a silencer/muffler is a better option. $\endgroup$– ratchet freakCommented Oct 27, 2017 at 16:10
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$\begingroup$ Welcome to Engineering Stack Exchange! This one has me stumped, and fluid mechanics is one of my proficient areas. Excellent question. In the future, always tag with the major branch of engineering for questions. $\endgroup$– MarkCommented Oct 27, 2017 at 16:41
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$\begingroup$ Wasn't that expanding gas bubble what Barbes Wallis used to destroy the dams ... so if we go with ratchet freak's silencer - how big would it need to be? Given that one on a car is 0.6m by 0.2m dia for a 1.8 or 2 litre engine.... $\endgroup$– Solar MikeCommented Oct 27, 2017 at 16:48
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$\begingroup$ Folks will often use a rupture disc in high speed applications. They are the fastest actuating of the protection methods with the downside of not resealing after lift/rupture. As an example these devices are used on high pressure low density polyethylene reactors (i.e. autoclaves) where ethylene decomposition can create very significant pressure increases in very short time periods. $\endgroup$– Byron WallCommented Nov 8, 2017 at 1:34
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2 Answers
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They are called blast valves. You need a delay loop in the pipe so the trigger can get ahead of the shock wave. Our interest was in closing off ventilation air conduits before the nuclear weapon's overpressure could penetrate the site.
See the pipe loops over the Launch Control Equipment Building? Those are the delay loops for ventilation air.
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I will propose a possible answer here. If you have an optical sensor in the pipe which detects the flash of the explosion, it may be possible to use that flash signal to open a pressure dump valve or a series of such valves prior to the arrival of the pressure wave at the downstream location you wish to protect. this solution uses the idea that the electric signal can be transmitted to the valve faster than the sonic velocity inside the pipe but it also requires a dump valve which can be opened very quickly. Ratchet freak may be right; dissipating the energy of the explosion may be the better answer, especially since it does not require instrumentation and fast-acting valves.
answered Oct 27, 2017 at 20:19