Super Soaker Central

Over spring break (next week for me), my science teacher has asked for us to build a model of a volcano and bring it in. They are supposed to explode in the form of their volcano type (example: if you're building a composite, it has to act like a composite volcano). I have decided that a good idea is to make a water gun type volcano with three PCs, one compressed air (pressure to be determined), one high pressure water (50 psi probably), and one low pressure water (10-30 psi).

The general build of the volcano will use 1.5" PVC for most of the body and the main nozzle, 3" for PCs, and 1/2" for the secondary and extra tubes (plans to be two for now).

If you don't know this, composite volcanoes are the hardest to make a model of; you have to have several openings and a boom, explosion, and trickle of lava (water).

If you have any suggestions, questions, or comments, post them please!

The biggest problem you are going to have is probably keeping the "lava" from shooting far. In a volcano, the lava doesn't shoot out like in a water gun. it has to trickle slowly. to do this you could either use very low pressure, or use a method I have had success with in the past.

When building a scythe for a school production of Macbeth I attached vinyl tubing with many tiny holes to the nozzle. (The scythe had to drip blood, so I used a small piston in the handle. The tubing was attached to the blade of the scythe) this resulted in a trickle of "blood".
A piston gun may be more useful for your purposes because you can get a trickle of water much more easily. Also, piston gun lack continous streams, which may be better for a volcano.
If you need an "explosion" you could have an auxiliary tank, which could be pressurized for a big blast. For added realism, you could add small rocks to the mix.
Here's a diagram

| oO0 |
|0Oo | Screen keeping rocks out of valve and water
VALVE
/ \
Pressurized water

The "lava" will be shooting straight up, and I don't think it should go far. Also, the high pressure PC will be an explosion, and the low-pressure will be a general trickle (the model doesn't have to be exactly perfect, and low pressure will give a continuos flow.

On a side note, I have bought basically all of my parts except for the few I haven't found yet. I will let you know on construction and when I am completed, shot pics. Also, I will be using high pressure schradors on my three chambers.

Lava's really viscous, so the model won't be exact. (Though that said fluid scaling laws are a bit complicated, change size and you must also change viscosity to get the same behaviour).

I'd want to try and have some of the same physical basis. What drives an explosive volcanic eruption is dissolved gases in the lava bubbling out. For a model, you could use a bottle of carbonated water, and find a way to suddenly release the pressure. Or you might be able to do something with a soda siphon or similar. Basically I'd want a 'magma chamber' full of fizzy water (bottle will do), a length of pipe or tubing (transparent if possible) for the vent, and a valve at the top (ball valve probably). You could perhaps put some sand or soil over the valve, to represent the existing rock that gets blasted skywards along with the magma.
Violence of the eruption should be controllable simply by shaking the magma chamber to varying degrees.

The one thing you probably can't reasonably represent is the thermal behaviour. I'd be surprised if you could model stuff like ashfall and pyroclastic flows with such a simple device.

Maybe I could use some carbonated water. That said, regular tap water is a lot easier to find.

It's true that the model isn't going to be exact, but the more realistic, the better. Maybe if there was a device to make a better pyroclastic flow would be better. I don't know if those exist.

Thank you so far for you're suggestions so far.

Btw, construction hasn't started yet, I have a lax toury this weekend plus a soccer game. On Mon., my family and I might go to CT for a few days and so building might be postponed to maybe Thursday.

I'd've thought you could get carbonated water cheaply in a supermarket. But you would face quantity limitations.

If you want to simulate the pyroclastic behaviour, you could go back to air-pressurised ideas. I don't know if you know how these flows arise. Essentially, the erupted material is hot. I thus heats the air around it, causing that air to rise and taking the material with it, forming and eruption column. The eruption column rises buoyantly. When the eruption ceases or reduces, the heat input is lost, and the column ceases to become buoyant and collapses. The descending air-ash mixture is diverted sideways when it approaches the ground, creating the pyroclastic flow.

Since it's probably not practical for you to create a buoyant mixture of air and dirt (though maybe a hairdryer or paint stripper gun could do it - the latter are dangeorous mind), you may have to instead adopt a dynamic approach. But if you try to blow dust upwards with pressurised air, it's probably going to just go sideways.

Anyway, I don't know off the top of my head how old you are. I have a degree in Geological Sciences, so I may be over-complicating things for your purposes. Probably a model that well relates to at least one aspect of the physics, at the expense of being a poor analogue in other ways, will be fine. Given I bet a lot of people will do methods like vinegar and baking soda (which tends to look the part with some dye, but the physical similarities are less).

Thanks, cantab, but I do not need that level of depth. You got it right; at least 85% of the class is primarily or somewhere using soda or baking soda. We had to tell our teacher our plans and she was surprised and taken aback because nobody had ever used PVC or actual pressure, just stuff like Diet Coke and Mentos.

I would be using a series of holes cut into the top of the volcano for the slower flow, with a gradual pressure release using a ball valve. For the fast release, I would probably have a couple of angled tubes to release water and soil and some small pebbles, but only pressurize it enough so that it can lift the objects above the rim a couple of inches. Oh, and you might want to substitute a more viscuous substance for the water that is in the slow flow.
-Zeda

make something that comes out fast, just for fun, make it look like an accident...but i suggest that you use low pressure but with a less viscous substance, use water with food colouring its the best chance of success

Well I guess it's time to talk about it more.

My air chamber didn't work, but the explosion was the best ever at the school - or that's what the teacher said.

Using forty PSI, my volcano shot fifteen feet up, into the air (also the highest ever) and I got drenched. But, it was definitely worth it!

I also added some baby powder and it added a smoke/ash feature that was rare for the particular assignment.

It was very sucessful, but now the paper cone of the volcano has crashed in and so getting a decent picture would be a difficult task.

This would actually be a good "booby trap" if you concealed it's chambers and piping, maybe underground. However, you'd have to trigger it nearby unless you put the PC a ways away and hid behind something using a hose. It would require more pressure or more water volumn but it would cause a surprise.

Btw, this is NOT a contest entry.

Good for you! nice to know that you made a big BANG

you could make it hand held and make it a single shot mega blaster!