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I need to release pressure of around 50psi, after 3-4 seconds of initiating, from a vessel using a mechanical switch. I had considered a pneumatic solenoid, but I want to forgo the inconvenience of charging the device with electricity in addition to the air, as well as save the space that would be needed for the bulky solenoid, circuitry, and battery.

I therefore need what would essentially be a "mechanical-fuse" that releases pressure after a delay when triggered. I considered a screw-type piston that gets forced along a track by the air in the vessel itself, which at a set psi could guarantee a specific time of release. I also need the system to be no longer than 5 inches along the axis of released pressure. Does a "screw-fuse" sound like a viable idea? Does anyone have any other sources for a mechanical fuse of this type, or an idea of their own?

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    $\begingroup$ a calibrated dampened piston would work, or a choke that restricts the airflow filling the piston. $\endgroup$ Apr 24 '15 at 8:04
  • $\begingroup$ Hmm...the choke idea is actually pretty good. Mechanically simple and easy to make... $\endgroup$ Apr 24 '15 at 23:48
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There are three possibilities here that come up offhand, between my own mind and ratchet freak's comment:

  • The choke that ratchet freak mentioned -- this is the simplest approach if you are OK with a slow decay of pressure
  • The dampened piston that ratchet freak also mentioned, where the mechanical switch pulls out a lock from the piston to allow pressure to retract it against the calibrated force from the damper
  • A clockwork mechanism that is triggered by the switch and provides the three-to-four second delay by letting a spring unwind

The main issue with the second and third mechanisms is that they would require some sort of manual or automatic reset functionality (a reset could be triggered by pressure building up to a certain point).

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  • $\begingroup$ I had indeed considered a wound spring, but it's not sturdy enough, and would obviously be more prone to breakage than the choke. I need the device to last as long as possible, so the fewer moving parts requiring maintenance the better. The choke is likely the method I will be going with. $\endgroup$ Apr 26 '15 at 15:13

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