How about a Steam Powered Pneumatic?

[moses]

Mythbusters tried to make a steam cannon, and it failed dismally.

[THUNDERLORD]

Mythbusters tried to make a steam cannon, and it failed dismally.

If I remember correctly, I thought they revisited it and it worked(?)
BTW, The water heater explosion was probably my favorite on there. 8)

[moses]

LOL @ water heater explosion. I daresay you are correct in regards to the re-visit.

[Hotwired]

@ MIT cannon

Heh. No countdowns or anything?

I bet £1 it's because the firing was too random.

The design was apparently too simple to share... like... ooh a burst disk cannon?

Have to be a hell of a burst material to hold up to 4000psi before blowing but I can see a heavy steel pipe with a burst disk and half a cup of water doing that.

After being baked in a fire pit for 20mins at 450*C...

[psycix]

...
How about this idea?
Using steam to compress the gasses to a higher pressure?

That diagram has got my gears turning.
The gray part would be a plunger or piston. I am thinking a spring could go inside the (shown) red part,
And a check (one way)valve, added to the valve end.
And a safety pop off on the steam chamber. Then coupled with or being a blow forward bolt design.

BTW, All the gasses that are stored as liquids are basically the same concept as water to steam, except they have lower boiling points.
They do yield different pressures though. I remember a chart for determining refrigerant types by measuring the pressure compared to temperature.

It is indeed an interesting idea!
THUNDER, note that it will be very hard to get a decent ROF out of that. It will take ages to heat the water.
One small steam powered gun I heard of (a small one) took 45 minutes to heat up. Enough time to load a new projectile by yourself, fix the target, drink a cup of coffee and whatever. A blow-forward will be unnecessary.
It would be a single shot gun.
I foresee a few problems:
-Heat. You may not want a few hundred degrees C steam passing trough your valve/barrel, but you will need to isolate the steam in the red part from the air in the blue area properly. And with a metal chamber, thats going to be hard.
-Pressure/volume. When the plunger/piston starts moving as steam builds up and expands, the pressure in the red part rises as the volume decreases. But for say, 20 bar, the volume has to be come 1/20th! That means that if your chamber would be 1 meter long, you will have left 5 centimeter (roughly two inches) of actual volume of air that goes trough the valve. And thats not alot of volume.
-Popoff on the steam? Watch out with that! You don't want to have very hot steam / flash boiling water blasting in your face!
-Other liquids? Maybe, but they will probably be less cheap then water and may have other unpleasant characteristics, besides maybe not being corrosive as water.

[sirspuddest]

It's already been built.

[frogy]

These have been made quite a few times before...

I once made one out of 5" of 1" steel to a 5/16" Brake line.... Airsoft BBs were great ammo, though they really didn't come out much over a few hundred fps (possible 500 fps)... I suppose that is decent for such a small and simple design though...

Note that you will need Leather gloves to turn the ball valve

[DYI]

I've always had some sort of interest in steam cannons, but the time and expense required to make a good one has always stalled my progress. I could build a steam cannon (I came up with a very comprehensive plan after I made my last thread about them), but it's always the reload time that kills it off. That, and the fact that a hybrid design that reaches the same pressure is usually easier to build, with a roughly equivalent SOS (although *really* hot steam can beat a propane hybrid's SOS).

The only kind of steam cannon I can see myself building would be a flash boiled electrothermal one, and it would have to be pretty small to be practical (although the possible hypersonic muzzle speeds would make it all worth while).

If you're going to build one, you might as well cut your costs and use a burst disk (perhaps a TBD valve?). You'll find though, that what seems to be a simple design will quickly become very complex indeed, mostly due to the somewhat uncommon materials required to take the heat/pressure loads.

I wish you all the best luck in building a good one, and hope you post it if you do.

[frankrede]

@frankrede it doesn't make much sense... that can be done with a pressure booster, a stirrup pump or an air compressor. USing steam to do it does not seem as the most efficient way...

...but you can build a steam engine to power an air compressor but I don't have enough knowledge to say if it would make sense or not

I don't see how it doesn't make sense, the water chamber would be heated causing th episton to compress the gas's even more without actually having an steam leave the barrel.
This would allow higher pressures to be reached than most air compressors and for a larger chamber that a hand pump wouldn't even want to take on.

[magnum9987]

It would require one huge water heater to make the cannon worth while.

In my opinion, i would by say a 50 gallon water heater (Am i correct in saying this is a restaurant sized water heater?).
In my quest for hypersonic i would hook it up to a 50 foot .5 barrel and go for ubber accuracy and power.

As ridiculous as it sounds, I want the POWER!
I would use a pneumatic valve if i had the money (which i never will get:( )

[frogy]

What is Magnum talking about? hahaha

I don't know if there are many pneumatic valves that can stand 300°F or more... I did see a SS valve rated for 400°F on McMaster a while ago though... I think it was something like $400

I heated my small steam gun up with a blow torch and turned a less-than-properly-pressure-rated ball valve with a leather gloved hand...

A large steam cannon is pretty impractical... I'd go hybrid if you want a large, powerful cannon.

I think a properly constructed steam cannon with a HP burst disk could be extremely powerful... Supersonic muzzle velocities with BBs should be relatively easy.

[D_Hall]

Inside the Tower of London there's a steam-powered gun that was developed as a faster-reloading firearm back in the days of muskets.

Yes, the idea is THAT old.

But hey, it works.

[SpudFarm]

and steam has low densety of what i can remember from my plans of making one (the speed of sound if high in the hot water vapors) but i did not want shock heating so i let it slip.

if i can find a big ass heat resistant safety valve, then i can do it