Wirtz pumps are really clever

- There's something weird about this pump. The spiral is one continuous channel. The whole thing is only 20 centimeters tall, but by turning it and periodically scooping up water, I can pump water substantially higher than 20 centimeters.

Thanks, by the way, to Ben Ainhorne for the idea for this video. I'll show you just how high the pump can push water a little bit later in the video. But first, how does it work?

Surprisingly, this pump works because of a principle that is normally incredibly annoying for engineers. I'm talking about airlock, and actually this gives me a perfect opportunity to correct a mistake that I made in a previous video about water solving mazes. I noticed in that video that water would stop flowing even though there was loads still in the tank.

That was surprising to me. There's a clear path through the maze, so why doesn't it empty out? I put it down to lots of little bits of surface tension adding up, but actually that's completely wrong, which is weird, because I've never made a mistake in a video before.

Thanks to many of you for pointing it out. Some of you, including Cory Albers, even brought receipts, and by receipts, I mean diagrams. What's really preventing the top tank from emptying is airlock, actually several airlocks one after the other.

The path of water through the maze is quite convoluted, so it's hard to see what's going on, which is why I built this setup. I've got a couple of taps here so that I can control the initial configuration of liquid in the tube. I can push water from here, and I can push air in through here.

So now we have these three U-shaped bits of tube filled with water, and these three N-shaped bits of tube full of air. Now this point is lower than this point, so surely, if I were to fill this up to that point, all the water would fall out and you might think, well, I suppose for the water to flow through, we have to overcome this hump here. We need to be able to push this water down with sufficient pressure to get over the hump, and then a kind of siphon effect will take care of it after that.

Well look, this is the height that we need to overcome and the height of water we have at our disposal is this, so that's plenty. We also need to overcome this hump, but again, that's shorter than the column of water we'll have when we fill this thing to the top, and this hump, which is also shorter. So why is it then when I pour the water in, there's a little bit of movement, but we get stuck?

Well, each one of these barriers is an airlock, and it turns out that airlocks are cumulative, like this column of liquid has to push this liquid up to the top here, but that liquid has to push this liquid to the top, and that liquid has to push this liquid to the top. So this column of water needs to supply enough pressure to push this water up, and what that water is pushing on over here, which includes what that water is pushing on over here, and so it all adds up. That means that if we want the water to drain, the height of this column needs to be greater than this height, this height, and this height added together, which it isn't, and that's exactly the problem we had with the maze.

It's harder to see, but we have a number of airlocks here, here and here. So no wonder the whole thing grinds to a halt when these three heights added together are greater than these heights added together. But for this compact little pump called a Wirtz pump, it means that we can push water to great heights.

Here's the thing, though. This video isn't going to be as simple as I was hoping it would be, and that's because this pump isn't behaving the way it's supposed to. Each one of these separate arcs of water is supposed to be acting as a plug that prevents air trapping between the different sections that are filled with water.

If air is bubbling through from one region to another, that's a failure of the pump. And if water spills from one region to another, that's a failure of the pump. And in fact, when operating the pump, the water doesn't go particularly high, or at least not as high as I would expect it to.

And that's weird, because these pumps definitely work on a larger scale. Look, if I hold the pump in this position, you can see the issue. This arc of water wants to fall down under gravity.

So does this one. And because airlocks are punitive, that should all add up. They should be able to fall down and push this water up here.

In other words, the pump should be able to operate to a much greater output height before it fails with bubbling and spilling and so on. I found one paper that said the cross-sectional area of the spiral pipes was important, and that about a centimeter and a half diameter would work, but they didn't explain what the issue is with narrower channels. So I sent an email to Jonathan Dean asking for advice, and brilliantly, he invited me to come and see the working pump he has at the bottom of his garden.

It just so happens to be close to where Matt Parker lives. So he's there in the background, look. I'm interested to see what's different about this pump compared to mine that doesn't work.

Also, Jonathan is here, and I have some questions for him. He'll tell me what size of pipe to use. I need to try and find a transparent version, otherwise it's not realistic.

Oh, I see it! Do you see that? (water sloshing) Now, this is interesting.

So you've got the spiral there, but then the hose comes out and you've got this big pickup here. That's the end that picks up the water, and it jumps into the middle there, goes around and around and around. That's because he wants to make sure that regardless of the level of the water, you're always gonna get some pickup.

You've got airlock several times in there, and just add up the pressures. And then of course, you've got these big paddles, and that's just a power thing. The rotator' hidden inside here, 'cause you've obviously got this but it isn't rotating, that, but there is rotating.

You need water to be able to pass through the tube without any kind of dripping. - [Jonathan] I deem at him and say you know, I've got one of these that rotates a million times in a season, and hasn't worn out. And they never emailed back.

(chuckling) - And this goes around and scoops up the water. And then this goes up a tube, right? But it didn't work, and that didn't work either.

That was remarkably worse. - See, this is quite small diameter pipe. You may need to use a bigger pipe.

But I think if the spiral is bunched tightly towards the outside like mine, with the big gap in the middle. - So the issue with it being small is what? - Surface tension.

- Okay. - So the water might not go in there very well, especially when you've got a pressure load on this side so it's actually pumping up. - You were saying if it's too big, if it's too wide, that's a problem as well.

- Yeah, so there's a great big pipe like that, you might have a problem because then you want to stay in spokes rather than the air bubbling through these ones. - And what were you saying about like see, I'm getting air coming up here. - [Jonathan] Now that's not bad.

That has to happen. So there's in between each plug of water, there's air, and the air gets pumped out just like the water gets pumped out. - And that means that like here, you can get your water even higher.

- Yes. - So you get a set amount of pressure built up there, and it it was just water, you could raise the water a certain height. - And it practically doubles that height, 'cause you've got air in there.

- [Steven] The outlet pipe terminates eight meters above the river into a water bog. Jonathan is able to create a bog habitat with this supply of water. But to have a bog garden, you need to really get the ground wet.

And, you know, you could use tap water, but that's terribly wasteful, so you're using the river to bog your garden, and it ends up back in the river. - Yes, it nearly always ends up back in the river. - Yeah.

- [Jonathan] So here comes. (water flowing) And then the overflow here goes back down to the bog garden, so it's circulating around. Now on winter, when I was inside, I found a tiny fish.

- [Host] Oh, really? - [Jonathan] And it had got pumped up, it was a minnow, from being in there all winter to grow. And I caught it in my net, put it back in the river.

- That's amazing. So I have a new Wirtz pump. This time, the tube is wider, and it doesn't spiral all the way into the middle, which means each turn of the coil is roughly the same circumference.

I forgot to explain why that's important. If the circumference of the inner segments gets too short, then you end up with a problem. A scoop of water that might take up, say, a third of the circumference of an outer segment will fill the whole circumference of an inner segment.

In reality, that just leads to bubbling and spilling over between the segments, as you can see here. Rotating couple here, so that should turn. It does.

Let's hope it doesn't leak. I'm also filming on the wide, so we can see how high up the water goes. Let's do a sync clap for that.

I've put white gaffer tape on the back so you can see where the water is, and I'm just turning it by hand. I haven't set up any complicated thing. (tubing squeaking) (birds chirping) Okay, here we go.

Come on. (birds chirping) Oh, come on. (birds chirping) Yes!

The benefit of me turning it by hand, and this is totally why I'm doing it this way, is at any point I can pull it out and you can see what's going on in there. Hopefully, I mean, it's hard for me to see from back here, but it looks like it's behaving as it should. It never got any higher than that, and if I ever turned it too fast, it would all collapse back down again, which is quite interesting behavior.

I wanted to see if I could use the thing to actually deliver water to a height, so I shortened that vertical tube to the point where I could hook it over that drain bracket. Come on! That is a working Wirtz pump if ever I saw one.

Isn't that fast I can go? Oh yeah, we're cooking now. (water dripping) Come on.

- [Jackie] Oh, good morning, am I speaking to Steven Mould? - Yes. - Great, can I just confirm your home address is?

(beeping) - Yep. - Ah, that's great. It's just Jackie calling from the Motor Vehicle.

. . - I've been fooled more than once by a phone call like that because the caller seems to know a lot about me, my home address, the car that I drive, but also they're calling from a plausible sounding, maybe governmental department.

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