I need of dire help (Air Solenoids valves)

[AlexHD]

Hello there!
I've been searching now for about 36 hours, and I cannot find a proper solenoid valve for my planned Supersonic Nerf cannon (Which could be fired semi-automatically).
Are the rated values are *really* the maximum you should go by?
I've thought to myself maybe if I use the valve for a more than it is rated for it still will hold, but then I will need to just add a little more voltage to the solenoid so it will actuate.
Overall, I would like some help to find the correct type of valve for this.
Currently the barrel is going to be 26-20" aluminum with ID of 13mm and walls 2mm Thick, A 4500psi Air tank with a regulator that is able to output 3000PSI.
Would like to find out about some new stuff if I can, maybe something along the lines of how much PSI should I output for a nerf dart to achieve supersonic speed.
Many thanks in advance!!

[mrfoo]

Can't help you with solenoids except to say that they're probably orders of magnitude too slow for what you want.

I can't even necessarily help with the latter part, but I can give some gut feel.

Would like to find out about some new stuff if I can, maybe something along the lines of how much PSI should I output for a nerf dart to achieve supersonic speed.

It's not pressure you need to worry about, at least not directly. If you want supersonic speeds, you're going to need supersonic flow, i.e. the gas pushing up behind the projectile is going to need to be going at supersonic speeds, all the way to the end of the barrel. You will need *at least* a convergent-divergent nozzle (de laval etc) to stop the gas choking its flow, otherwise the strict maximum you're going to get, regardless of pressure, is mach 1. You're also going to need to worry about accelerating the as *in front* of the projectile to supersonic speeds, and it will not want to do so Flow will choke, and you will have a shock wave in front of the projectile. There's a very good reason most supersonic air cannons use an evacuated barrel.

And then you have to worry about valve speed. You're going to need total opening within microseconds. A 26" barrel is 2/3 of a metre, and you want your projectile moving at over 350m/s, time in barrel to get that is at best, something of the order of the order of 3 milliseconds. Again, most supersonic air cannons use burst disks.

[farcticox1]

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