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[Servu]

So I am planning to build a little magma cannon to my new fort and need some information. Firstly, I am thinking of using the source volcano as a pressure cistern, and secondly I need to keep my fortress in the bottom unflooded. Here is my initial design:

Code: [Select]

[Side]
###     #########
###~~~~~#########
###~~~~~~~~######
###~~~~~##~######
###~~~~~##~######
///////////////// (the rest of the 80 z-levs)
###~~~~~##~######                ##HFS#
###~~~~~##~######                ##HFS#
###~~~~~~~~~~~~X                 ##HFS#
###~~~~~#########                ##HFS#
###~~~~~##<F>___X   E E E        X_HFS#
###~~~~~~~~########################HFS#
Legend:
~ Magma
# Rock
X Floodgate
<F> Forge
E Unsuspecting forest hippie elf
HFS as itself

The idea of the system would be to dig a secondary magma pipe aside the original one so the sweet fiery death gains a mighty pressure, now what I am not sure of is whether the pressure is nullified if the actual cannon has a direct access to the volcano. I guess it would not be necessary to directly connect these two from the bottom, but I figure the amount of magma involved would give the cannon some more power behind it. If the pressure is nullified I can always use a cistern.

The second problem is that my fort needs the magma too, and if the pressure is transmitted I'll end up with a rather large magmaplosion on the wrong side of the front door.

Lastly, draining all that magma will be a chore and in the absence of a chasm I was thinking of using the HFS to drain the place after firing (note that it (probably) is almost as high as the volcano). I know this will lead to Fun, but thats pretty much why I am trying.

Then there is the usual question of if the cistern or the cannon mouth should be made out of steel/adamantium (yes) and what should it look like. Also the possibility of an 80 level magmafall when the cannon is offline.

[decius]

Magma will only transport if it is being pushed by a pump. I'm pretty sure that it will only move at the pump rate as well. So, you need a battery of pumps connected to motive power.

[Jim Groovester]

Magma doesn't build up pressure like you're thinking of it. If you want to do what you're trying, you'll need pumps, and you'll probably want a pump tower near the base of the magma pipe for what you're going for.

Why a pump tower? So you'll get the pressure you're describing. And so you don't run out of magma as quickly.

[Servu]

Magma doesn't build up pressure like you're thinking of it. If you want to do what you're trying, you'll need pumps, and you'll probably want a pump tower near the base of the magma pipe for what you're going for.

Why a pump tower? So you'll get the pressure you're describing. And so you don't run out of magma as quickly.

Hmm, so magma does not gain pressure by falling z-levels then? I have been reading the wiki wrong. I thought the sheer altitude of the volcano would have done the thing.

[Jim Groovester]

Hmm, so magma does not gain pressure by falling z-levels then? I have been reading the wiki wrong. I thought the sheer altitude of the volcano would have done the thing.

That is correct. Only water gains pressure by falling.

What page of the wiki misled you? It's important to get that inaccurate reference in check.

[Servu]

What page of the wiki misled you? It's important to get that inaccurate reference in check.

http://dwarf.lendemaindeveille.com/index.php/Magma

There was described that magma raises back to it's original z-lavel after going through a pump

Magma that is emerging pumped from a screwpump will behave as if pressurized

I was planning to build a single screw pump on the top to enable the pressure.

edit: I suppose the keyword here is behave as if pressurized. So it still doesn't get any other pressure effects, just raises slowly back?

[Albedo]

Hmm, so magma does not gain pressure by falling z-levels then? I have been reading the wiki wrong.

em... meh.  <stifles>

You have not been reading the complete articles, or the ones that actually address the topic, because they're pretty clear.  DF "pressure" is not "PSI", never, never, ever.

Read wiki: "pressure".

[Jim Groovester]

Well, hell, you didn't mention the screw pump. That's an important detail.

If you have a pump at the top:

Your magma forges will flood. The pump will look for places to deposit magma, and your forges have empty space.

Your magma cannon should work, though it won't work the same ways as a similarly tall water tower. Your secondary magma pipe won't empty immediately, but the pump will still make magma come out of the cannon.

When pumping magma, it's the pump that's doing the pressurizing, not the magma itself. The pump just looks for an open place to put the magma, and places it there, but the magma still behaves like magma. This gives it the appearance of pressure, but there are still differences. Primarily, magma won't empty itself all at once if given the chance like water does.

[Servu]

Ah ok. I think I got it now. Will probably stick with the magmafall then. Thanks for clearing this up for me.

[Ruttiger]

You can still have a magma cannon by placing a lot of magma pumps in parallel with each other.  It's not going to shoot lava out, but it should flood the target area fast enough that that shouldn't matter.

I built one with five screw pumps.  Other than the fact I have no way to clean up the mess it works quite well.