And I thought magma was pushed from the semi-molten rock up to the natural limit of the magma sea...
That's unfortunate. Channeling probably won't have that much flow. You can add a pump closer to the map edge, with a strait tunnel to direct the magma to your stack. Power it with a long horizontal shaft from the stack. Sure it will take more power, but the flow will be more than sufficient. Lots of planning and digging...
Thanks. I was thinking about building into magma sea from above, after depleting current level of magma. But that would be dangerous, and in need of constant attention - because of creatures. Not really funny. Or using water to build walls. But your idea should work, though I'd need more than one pump - z-level below is also cut off. Since my pumpstack is devised to use only 2/3 of power of my reactor I should be able to transfer enough power through wooden axles. I hope they won't burn.
The magma pipe will refill overtime, magma will spawn in pillars the come up from the surface and spread out.
Magma pipe is another name for magma sea? I'm pretty sure that the topmost level in my locations doesn't refill, because I have left it for a year. I think that square with Magma Flow may refill, as opposed to Empty Space.
To achieve good pumping speed your pumps should draw magma from every side but not on the top level. If you dig down you need to breach the pipe to get magma but even if you can breach 10 adjacent blocks flow will still be an issue.
If you are lucky somewhere deep in the magma sea you can find a spot where mineable rock overhangs the magma sea with 20-30 levels of magma reserves above you. If you are real lucky there will be a stalactite of mineable rock that hangs into the magma sea and is wide enough to build a pump stack down. At the bottom of one of these magma can flow to your pump intake square from all sides and from above on all sides as well.
Your pump is in a bad location being too close to the edge, and on the top layer.
I would recommend a re-build using the method in this thread;
http://www.bay12forums.com/smf/index.php?topic=67905.msg1627359#msg1627359
start in the center and pump that z-level dry (fortifications off the edge of the screen) then hang up/down stairs down into the pipe, build one floor and put the next pump on that. I made a two-wide stair on the side of the pumps instead of putting them on the end as the diagram does not show how half the grey floors are attached to the stairs. Go as many levels deep for as much magma you want at once then let it re-fill which will take some time. Your pumps will need to operate constantly when building it or you'll be overflowing with !!FUN!!
You won't need walls around the stack because the pumps can pick up fluids faster then they can fall away from the pump below it.
The output should be fast enough to run though a channel over to your other pumpstack at the edge of the magmapipe without losing flow.
My stack is in fact near middle of the map. This is just the edge of on one of "lakes", but they are all connected, two z-levels below. But yeah, if I wasn't forced to attend other experiments I would use your method to build into sea. Heck, later I'll probably will do it out of curiosity. But that number of idlers in my screenshot is unusual, I have no more than 5 idlers normally, unless they are finished with something.
EDIT: Oh, and the location is chosen by coincidence. I was digging a a vertical shaft looking for magma and found SMR. Then I made some horizontal shafts one level higher and found SMR. Then again and again. Finally I got minable rock five levels higher and that was the place on top most level of magma sea. But probably there are breaches in SMR somewhere, so maybe I'll find them.