Solenoid Valve Controlled Pneumatics

[Swany]

Not too much to say, basically you get a sprinkler solenoid, build an air chamber, put the solenoid in between the barrel and the airchamber, modify the solenoid such that when you vent air, it fires, and you have a very fast diaphram valve.

 

The solenoid operates such that when you vent some air from it, the pressure difference opens a diaphram which vents out your whole air chamber very fast, thus propelling old marshmallows at speeds that will dent sheet metal.

 

Look at spudfiles.com for the knowhow, as I am pressed for time and may later edit with more info. Great fun though!

 

My latest cannon cost about 50$, and half of it was the valve/blowgun/tirevalve(so it could be pressurized)

 

Attached is a picture of the valve assembly.

[waxman]

Swany- How does your pneumatic cannon compare with the MAPP gas combustion gun?

[Swany]

Depends on what you're trying to say. If you are saying 'I want to use a simple combustion gun that uses MAPP/air versus a solenoid cannon; the solenoid is more powerful.

 

MAPP gas will produce about 40 PSI in a combustion gun. My gun has 120 PSI stored in it. Combustion guns have more effecient air transfer as the 'valve' is not restricting, pneumatic's valves restrict airflow, but the increase in pressure makes up for it.

 

If you have an air compressor, or a bike pump and endurance, go for the pneumatic. If you want to carry it around lots, go for the MAPP. Both are loud to some degree, but combustions are louder, inherently.

[waxman]

Thanks Swany. I'd have guessed the combustion gun would produce higher pressures than 40 psi. Do you know if a "hybrid" has been tried? I mean a pneumatic action that compressed an air/fuel mixture to the point of ignition. Sort of a diesel spudgun. I know- weird. Just wondered!

[Swany]

Hybrids involve using a burst disk, adding extra air, say, 5 bar (70PSI) and then adding 5x the normal amount of fuel, say you use propane, you would add 20% by volume rather than 4%, as is stoich at STP.

 

Flooding the chamber with oxygen and a fuel is a no-no. Real chance of detonation, and that would mean roughly 10 times the pressure of deflagration. Acetylene and air detonates at roughly 4000PSI, though propane and air are about half that. Your chamber would not like that. Detonation is much more brutal to your chamber rather than if you slowly raised the pressure to however many thousand PSI as well. A sudden jar in pressure, say a salute in a PVC tube, is more likely to shatter it than if you were using even nitrocellulose as your propellant. At least for Sam Barrows (egotistical asshole, but still).

 

Realise that your chamber is 80% inert gasses when you fire your combustion.

[waxman]

According to the GexCon Handbook of Explosive gases-

Table 4.5. Pressure, P, (absolute) and volume ratio (V/V0) for Stoichiometric fuel-air mixture at initial conditions 25° C and 1 atm (1.013 bar) (Baker et al. 1983).

 

Hydrogen

Ethylene

Propane

Methane

 

P (bar)

8.15

9.51

9.44

8.94

 

V/V0

6.89

8.06

7.98

7.72

 

The table doesn't show it here, but it says propane developes 9.44 bar when popped in a stoch mixture with air at atm. (140 psi)

I'm wondering now what the pressure is during a propane shot. You're saying 40 psi, they're saying 140 psi. Call me confused!

[Swany]

That may be in confined tubes, measuring pressure with a schrader valve or some other instrument. We have a potato plug that leaves the scene fairly quickly.

[Ozzy]

This is her 6'4 18Lbs

 

http://i9.photobucket.com/albums/a94/ozzyKKK/S4024629.jpg

 

http://i9.photobucket.com/albums/a94/ozzyKKK/S4024628.jpg

 

http://i9.photobucket.com/albums/a94/ozzyKKK/S4024626.jpg

[Pont]

Resize maby that pic is so big I couldnt tell what I was looking at and took me a while to find the reply button..