Recreating an Ancient Pump (with no moving parts)

0:01 On the hill above Granada, Spain, sits the Alhambra:

0:04 a medieval palace and fortress complex of the historic Islamic world.

0:09 Built and modified over centuries,

0:11 the Alhambra is now a UNESCO World Heritage site

0:14 and stands as one of the best-preserved palaces in the world.

0:19 Every city needs a reliable source of water,

0:21 and that stood as a challenge for the Alhambra,

0:24 perched high above the nearby rivers.

0:26 Medieval engineers used a lot of creative solutions to divert

0:30 natural sources of water and distribute it to the cisterns,

0:33 baths, and fountains within the complex.

0:35 Another YouTube channel, Primal Space,

0:37 has an excellent video on all the ingenious ways they managed water,

0:42 and one of the details in that video really caught my imagination.

0:46 Alcazaba is the stone fortress on the western tip

0:49 of the Alhambra that sits higher than most of the palace city.

0:53 Apparently, throughout the Renaissance (and maybe

0:55 even starting in the medieval period),

0:57 the fortress was supplied by water using a pump that had no moving parts.

1:02 In 1764, a priest observed the device.

1:05 He couldn’t understand how it worked, but he did his best to describe it anyway.

1:10 More than a century later, a Spanish engineering professor, Cáceres,

1:13 took it upon himself to try

1:15 and recreate the device using the priest's description.

1:18 By that time, remnants of the device were gone.

1:22 Historians estimate it existed until the end of the eighteenth century,

1:25 when a higher canal replaced it.

1:27 Even so, the professor got it to work,

1:30 presenting his results at a 1911 scientific congress in Granada.

1:34 Was it the actual pump design the priest described?

1:37 We’ll never know for sure, but it seemed likely to that professor,

1:40 and more recent historians have found it plausible.

1:43 And that’s pretty fascinating to me.

1:45 A pump with no moving parts, able to lift water above its source,

1:50 quietly serving a hillside fortress centuries ago.

1:53 It is clever, effective, and, all these years later, mostly unknown today.

1:57 You can’t pick one up off the shelf

2:00 at your local hardware store, at least not yet.

2:03 So I decided to take after Professor Cáceres and try to build one myself.

2:08 I’m Grady, and this is Practical Engineering.

2:20 There’s something really magical about taking

2:22 advantage of flowing water to accomplish work.

2:26 I don’t know exactly what it is.

2:28 Seeing a natural force, like the flow of a river,

2:31 interacting with human ingenuity to do

2:33 something important- it’s really cool to me.

2:36 And it’s especially cool when it’s purely mechanical.

2:39 Don’t get me wrong; I love electronics, circuits, and sensors.

2:43 But doing a job with water alone- you

2:45 have to admit that there’s something special about it.

2:48 I’ve covered a few devices like this before.

2:50 I built a trompe, which is basically a water-powered compressor.

2:54 I also built a ram pump,

2:56 which is a water-powered pump that uses check valves to harness kinetic energy,

3:00 converting it to pressure.

3:01 But I have to admit that Primal Space’s video is the first time I had

3:06 ever heard of what seems to be mostly referred to nowadays as a pulser pump.

3:10 And there really isn’t much information out there about them,

3:14 despite the fact that they’ve been around for centuries.

3:17 The idea isn’t really that complicated, but the details are a little tricky,

3:21 so I decided I would try to come up

3:23 with a design that boils it down as simply as possible.

3:26 And you know we have to break out the acrylic.

3:29 Actually, most of the parts for this demonstration

3:31 came from my friends at Send Cut Send, who sponsored this video.

3:35 I could buy sheets of acrylic and cut all this out myself,

3:38 and I’ve done so much of that, but just look at this.

3:41 An entire idea from my head shipped to my door.

3:44 The quality’s better, the cuts are way more precise than I would make,

3:48 and I don’t have a day's worth of measuring, cutting, and cleaning up to do.

3:51 I can’t recommend Send Cut Send enough.

3:53 If you have projects that use sheet goods, give it a try at the link below.

3:57 I really appreciate their support.

4:00 I just had to tap the holes… then glue everything together.

4:03 Now, let’s turn on the water so we can see this in action.

4:07 Step one is this basin up top.

4:09 Rather than connecting directly to the hose,

4:12 I wanted a free surface of water at the top,

4:14 just so it’s clear, from an energy perspective, that this is the starting point.

4:19 This tank provides a simple, consistent, and obvious input for the pulser pump.

4:24 It’s the equivalent of the end of a canal in an ancient palace,

4:28 and the goal is to raise the water above this level.

4:31 From the basin, the water falls down this vertical pipe.

4:34 But if you look carefully, you can see it’s not just water.

4:38 The water flows into this tee fitting that acts like a vent,

4:41 allowing the stream to kind of swirl around and draw in air.

4:44 There are quite a few ways to intentionally mix air and water.

4:48 The historical description of the pump at the Alhambra

4:51 was pretty unclear when it comes to this part.

4:54 The priest didn’t provide much detail about how

4:56 the air was entrained in the downward flow.

4:59 Professor Cáceres tried two methods and had the most

5:02 success using a whirlpool to draw water and air downward.

5:05 I don’t know if this is exactly what he tried,

5:08 but it is dead simple, and it worked surprisingly well.

5:12 You can see the water in the pipe is full of bubbles,

5:15 and it’s moving fast enough to carry them into the next tank.

5:19 The goal in this area is to separate all the air from the water.

5:23 You can see the bubble float upward while most of the water continues onward.

5:27 The sloped top helps trap the bubbles,

5:30 so the flow exiting on the right is just water.

5:33 So far, this is basically just a trompe.

5:35 I mentioned I built one of these before

5:37 in my backyard and made a video about it.

5:39 It looks a little different from this one,

5:41 but the concept is basically the same.

5:43 Entrain bubbles of air in a stream of water, carry them downward,

5:47 and then separate them out- now under pressure- so

5:50 the air can be used for things like smelting,

5:52 powering tools, or in my case, blowing some dry grass around.

5:57 It was just a scale demonstration.

5:59 Trompes aren’t used much these days.

6:01 It’s easier to buy a compressor than to build a piece of infrastructure.

6:05 But it’s still a cool idea,

6:08 and their use is being explored to aerate remote pools of mine

6:12 waste to speed up the bacterial reactions that can help clean up contamination.

6:16 There are probably quite a few edge cases where a source

6:20 of pressurized air is more valuable than a source of moving water,

6:24 and a trompe basically lets you make

6:26 that trade with no moving parts or electricity.

6:29 You can see in my model,

6:31 there’s a riser on the right, just like with the trompe demo.

6:34 The purpose of this is to create

6:36 enough pressure to encourage the bubbles upward.

6:38 You can imagine if there was no back pressure on the system

6:41 and I just let the water out at the bottom of the separator,

6:44 eventually it would just fill up with air.

6:47 That’s not what we want.

6:48 So the water has to flow up the riser and then out through this hose,

6:53 keeping the bubbles under pressure so that they’ll flow out of this tube:

6:58 the discharge line for the pump.

6:59 I tried all this in my garage first,

7:02 but kept spraying the ceiling, so I eventually decided to do this outside.

7:06 My discharge line runs up above the inlet tank.

7:09 As bubbles move into the separator, they float upward and out of this pipe.

7:14 But, because the pipe is pretty narrow,

7:17 water gets kind of trapped between the bubbles.

7:20 This is a little finnicky, but basically,

7:22 the buoyancy of the air mixed with the water occasionally creates enough

7:26 lift for the water to make it all the way to the top.

7:29 And now you can see why they call this a pulser pump.

7:32 You don’t get a very continuous flow.

7:34 But look at that!

7:36 The water is actually going a lot higher

7:39 than where it started in the upper tank.

7:45 We are moving water uphill with no moving parts.

7:49 Actually this part of the pump is a pretty ubiquitous design.

7:53 It’s usually called an air lift pump.

7:55 Basically, pump air bubbles to the bottom of a pipe,

7:58 and let them carry water upward.

8:00 These are often used in dirty situations where you don’t want sand,

8:04 grit, or plant matter clogging up the impeller of a more traditional pump.

8:08 They’re not very efficient,

8:09 but useful in certain situations like wastewater plants and dredges.

8:13 And, this is also how coffee percolators work.

8:16 The steam bubbles carry the liquid water to the top

8:19 where they can percolate downward through the grounds.

8:22 I’m recirculating the water in this demo just

8:25 using a bucket and pump below the table,

8:27 and that drives home a couple of key points here.

8:30 For one, all the water running through the pump does not actually get pumped.

8:34 In fact, in my little demo here, I didn’t actually measure it,

8:38 but I’d guess the discharge flow rate is somewhere less

8:40 than five percent of the total flow rate through the pump.

8:44 You need a lot of water to move just a little bit upward.

8:47 So for two, this is not a free energy device

8:50 in the same way a hydropower turbine isn’t producing free energy.

8:54 In a practical sense, the pulser pump is extracting energy

8:58 from the flowing water to push water bubbles downward,

9:02 temporarily storing the energy.

9:04 Then it’s extracted again to push some of that water back up.

9:13 So it really is that simple.

9:15 A pulser pump is basically a combination of two steps:

9:18 a trompe to supply the bubbles,

9:20 and an air lift pump that uses those bubbles to carry water upward.

9:24 But in some ways, it’s not simple at all.

9:28 Two phase flow, where air and water move together, is pretty complex.

9:32 If you thought fluid dynamics was tricky with one fluid, just try using two!

9:37 You can tell just by looking at my demo

9:39 that there’s not a lot of stability here.

9:41 At the down tube, sometimes you get a regular stream of small bubbles,

9:45 and occasionally you get one big one.

9:48 At the discharge, sometimes you get regular pulses;

9:50 sometimes you get big bursts.

9:52 Every step of the process is just so …gurgly.

9:57 There are a lot of knobs to turn here,

9:59 and they all affect the system in different ways.

10:02 Let’s say you have a fixed flow rate,

10:04 and a fixed amount of height between your inlet and outlet.

10:08 You still have to select the diameter of your down pipe,

10:10 which will affect the fluid velocity, and so how much air you can draw in.

10:14 There are probably many different ways to mix

10:16 the water and air that are more or less efficient,

10:19 depending on the configuration.

10:21 And there’s the diameter of the discharge line.

10:23 A bigger pipe can move more water,

10:25 but too big and the bubbles don’t crowd up enough to carry water with them.

10:30 There is quite a bit of engineering guidance out there for air lift pumps,

10:34 since they’re pretty widely used.

10:35 Not so much for trompes, although I did find an interesting paper

10:39 in the Journal of Applied Thermal Engineering.

10:42 The author called them “hydraulic air compressors” and that’s actually one

10:45 of the tricky parts to finding more information on devices like this.

10:50 Since they’re pretty obscure, there’s not much consistency in terminology.

10:54 The most I could find on pulser pumps

10:56 was a few old YouTube videos and college projects.

11:00 And this recent paper on the hydraulic techniques for water supply

11:04 at the Alhambra doesn’t even venture a name for the device used there.

11:08 So this is still kind of just trial-and-error engineering.

11:11 I’m sure I could spend hours

11:13 trying different configurations and improving this demonstration.

11:16 If you’re a grad student looking for a thesis idea,

11:19 I think pulser pumps would make a pretty interesting project,

11:22 because I can see some applications here.

11:24 In fact, I’m not the only one.

11:26 Hydraulic ram pumps are pretty popular around the internet

11:29 and in rural areas that have abundant water but no electricity.

11:33 They were well known by the time Professor Cáceres did his experiment in 1911.

11:38 In his paper, he said about the pulser pump: “This arrangement will always have,

11:43 over the hydraulic ram, the advantage of eliminating valves entirely,

11:48 since it contains no moving solid parts.

11:50 Doing away with the ram strokes seems to remove

11:53 any source of fatigue in the pipes and, of course,

11:56 the very annoying noise that makes the ram inapplicable near living

12:00 quarters.” I can’t help but think back to him in his lab,

12:03 seeing the water spurt out from the top

12:05 of the discharge line for the first time.

12:07 You can tell his excitement in the paper:

12:10 “Beyond its historical appeal, the idea has real value for modern engineering.

12:14 In cases where efficiency is not critical,

12:17 reviving it could solve practical problems,

12:19 using a layout so simple that it is remarkable

12:23 it has not become common knowledge after several centuries.” I

12:27 wonder if he would be a little disappointed

12:29 that the idea never really did catch on, despite its novelty.

12:33 But I still think it’s pretty cool.

12:35 And maybe someone will see my demo working and try it for themselves,

12:39 carrying the ancient idea forward for new applications.

12:42 Thank you for watching, and let me know what you think!