Recreating an Ancient Pump with No Moving Parts

[00:01] On the hill above Granada, Spain, sits the  Alhambra: a medieval palace and fortress   complex of the historic Islamic world. Built  and modified over centuries, the Alhambra is   now a UNESCO World Heritage site and stands as  one of the best-preserved palaces in the world.

[00:19] Every city needs a reliable source of water,  and that stood as a challenge for the Alhambra,   perched high above the nearby rivers. Medieval  engineers used a lot of creative solutions to   divert natural sources of water and distribute it  to the cisterns, baths, and fountains within the  

[00:35] complex. Another YouTube channel, Primal Space,  has an excellent video on all the ingenious ways   they managed water, and one of the details  in that video really caught my imagination. Alcazaba is the stone fortress on the western  tip of the Alhambra that sits higher than most  

[00:52] of the palace city. Apparently, throughout  the Renaissance (and maybe even starting   in the medieval period), the fortress was  supplied by water using a pump that had no   moving parts. In 1764, a priest observed the  device. He couldn’t understand how it worked,  

[01:07] but he did his best to describe it  anyway. More than a century later,   a Spanish engineering professor, Cáceres, took it  upon himself to try and recreate the device using   the priest's description. By that time, remnants  of the device were gone. Historians estimate it  

[01:23] existed until the end of the eighteenth century,  when a higher canal replaced it. Even so,   the professor got it to work, presenting his  results at a 1911 scientific congress in Granada. Was it the actual pump design the priest  described? We’ll never know for sure,  

[01:38] but it seemed likely to that professor, and more  recent historians have found it plausible. And   that’s pretty fascinating to me. A pump with no  moving parts, able to lift water above its source,  

[01:50] quietly serving a hillside fortress  centuries ago. It is clever, effective,   and, all these years later, mostly unknown  today. You can’t pick one up off the shelf   at your local hardware store, at least not  yet. So I decided to take after Professor  

[02:05] Cáceres and try to build one myself. I’m  Grady, and this is Practical Engineering.

[02:20] There’s something really magical about taking  advantage of flowing water to accomplish work.   I don’t know exactly what it is. Seeing a  natural force, like the flow of a river,   interacting with human ingenuity to do something  important - it’s really cool to me. And it’s  

[02:36] especially cool when it’s purely mechanical.  Don’t get me wrong; I love electronics, circuits,   and sensors. But doing a job with water alone -  you have to admit that there’s something special   about it. I’ve covered a few devices like this  before. I built a trompe, which is basically  

[02:53] a water-powered compressor. I also built a  ram pump, which is a water-powered pump that   uses check valves to harness kinetic energy,  converting it to pressure. But I have to admit   that Primal Space’s video is the first time I had  ever heard of what seems to be mostly referred to  

[03:08] nowadays as a pulser pump. And there really  isn’t much information out there about them,   despite the fact that they’ve been around for  centuries. The idea isn’t really that complicated,   but the details are a little tricky, so  I decided I would try to come up with a  

[03:24] design that boils it down as simply as possible.  And you know we have to break out the acrylic. Actually, most of the parts for this  demonstration came from my friends at   Send Cut Send, who sponsored this video. I could  buy sheets of acrylic and cut all this out myself,  

[03:38] and I’ve done so much of that, but just  look at this. An entire idea from my head   shipped to my door. The quality’s better, the  cuts are way more precise than I would make,   and I don’t have a day's worth of measuring,  cutting, and cleaning up to do. I can’t recommend  

[03:52] Send Cut Send enough. If you have projects that  use sheet goods, give it a try at the link below.   I just had to tap the holes… then glue   everything together. Now, let’s turn on  the water so we can see this in action.

[04:07] Step one is this basin up top. Rather  than connecting directly to the hose,   I wanted a free surface of water  at the top, just so it’s clear,   from an energy perspective, that this is the  starting point. This tank provides a simple,  

[04:21] consistent, and obvious input for the  pulser pump. It’s the equivalent of the   end of a canal in an ancient palace, and the  goal is to raise the water above this level. From the basin, the water falls down this  vertical pipe. But if you look carefully,  

[04:36] you can see it’s not just water. The water flows  into this tee fitting that acts like a vent,   allowing the stream to kind of swirl around  and draw in air. There are quite a few ways   to intentionally mix air and water. The historical  description of the pump at the Alhambra was pretty  

[04:52] unclear when it comes to this part. The priest  didn’t provide much detail about how the air was   entrained in the downward flow. Professor Cáceres  tried two methods and had the most success using   a whirlpool to draw water and air downward. I  don’t know if this is exactly what he tried,  

[05:08] but it is dead simple, and it worked  surprisingly well. in the pipe is full of bubbles, and it’s moving  fast enough to carry them into the next tank. The goal in this area is to separate all the  air from the water. You can see the bubble  

[05:24] float upward while most of the water continues  onward. The sloped top helps trap the bubbles,   So far, this is basically just a trompe. I  mentioned I built one of these before in my  

[05:38] backyard and made a video about it. It looks a  little different from this one, but the concept   is basically the same. Entrain bubbles of air  in a stream of water, carry them downward,   and then separate them out - now under pressure -  so the air can be used for things like smelting,  

[05:52] powering tools, or in my case, blowing some dry  grass around. It was just a scale demonstration. Trompes aren’t used much these days. It’s easier  to buy a compressor than to build a piece of  

[06:05] infrastructure. But it’s still a cool idea, and  their use is being explored to aerate remote pools   of mine waste to speed up the bacterial reactions  that can help clean up contamination. There are  

[06:17] probably quite a few edge cases where a source of  pressurized air is more valuable than a source of   moving water, and a trompe basically lets you make  that trade with no moving parts or electricity.

[06:29] You can see in my model, there’s a riser on the right, just  like with the trompe demo. The purpose of this   is to create enough pressure to encourage the  bubbles upward. You can imagine if there was   no back pressure on the system and I just let  the water out at the bottom of the separator,  

[06:44] eventually it would just fill up with  air. That’s not what we want. So the   water has to flow up the riser and then  out through this hose, keeping the bubbles   under pressure so that they’ll flow out of  this tube:

[06:58] I tried all this in my garage first, but kept  spraying the ceiling, so I eventually decided   to do this outside. My discharge line runs up  above the inlet tank. As bubbles move into the  

[07:11] separator, they float upward and out of this  pipe. But, because the pipe is pretty narrow,   water gets kind of trapped between the bubbles.  This is a little finnicky, but basically,   the buoyancy of the air mixed with the water  occasionally creates enough lift for the water  

[07:27] to make it all the way to the top. And now you  can see why they call this a pulser pump. You   The water is actually going a lot higher than where it started in the upper tank.

[07:45] We are moving water uphill with no moving parts. Actually this part of the pump is a pretty  ubiquitous design. It’s usually called an air lift   pump. Basically, pump air bubbles to the bottom  of a pipe, and let them carry water upward. These  

[08:00] are often used in dirty situations where you don’t  want sand, grit, or plant matter clogging up the   impeller of a more traditional pump. They’re not  very efficient, but useful in certain situations   like wastewater plants and dredges. And, this  is also how coffee percolators work. The steam  

[08:17] bubbles carry the liquid water to the top where  they can percolate downward through the grounds. I’m recirculating the water in this demo  just using a bucket and pump below the table,   and that drives home a couple of key  points here. For one, all the water  

[08:31] running through the pump does not actually  get pumped. In fact, in my little demo here,   than five percent of the total flow rate  through the pump. You need a lot of water  

[08:45] to move just a little bit upward. So for two,  this is not a free energy device in the same   way a hydropower turbine isn’t producing free  energy. In a practical sense, the pulser pump  

[08:57] is extracting energy from the flowing water  to push water bubbles downward, temporarily   storing the energy. Then it’s extracted  again to push some of that water back up.

[09:13] So it really is that simple. A pulser pump  is basically a combination of two steps:   a trompe to supply the bubbles, and an air lift  pump that uses those bubbles to carry water   upward. But in some ways, it’s not simple at all.  Two phase flow, where air and water move together,  

[09:31] is pretty complex. If you thought fluid  dynamics was tricky with one fluid,   just try using two! You can tell just by  looking at my demo that there’s not a lot   of stability here. At the down tube, sometimes  you get a regular stream of small bubbles,  

[09:45] and occasionally you get one big one. At the  discharge, sometimes you get regular pulses;   sometimes you get big bursts. Every step  of the process is just so …gurgly.

[09:57] There are a lot of knobs to turn here, and they  all affect the system in different ways. Let’s say you have a fixed flow rate, and a fixed  amount of height between your inlet and outlet.   You still have to select the diameter of your  down pipe, which will affect the fluid velocity,  

[10:12] and so how much air you can draw in. There are  probably many different ways to mix the water and   air that are more or less efficient, depending  on the configuration. And there’s the diameter   of the discharge line. A bigger pipe can move  more water, but too big and the bubbles don’t  

[10:27] crowd up enough to carry water with them.  There is quite a bit of engineering guidance   out there for air lift pumps, since they’re  pretty widely used. Not so much for trompes,   although I did find an interesting paper in  the Journal of Applied Thermal Engineering.  

[10:42] The author called them “hydraulic air  compressors” and that’s actually one of   the tricky parts to finding more information on  devices like this. Since they’re pretty obscure,   there’s not much consistency in terminology. The  most I could find on pulser pumps was a few old  

[10:58] YouTube videos and college projects. And this  recent paper on the hydraulic techniques for   water supply at the Alhambra doesn’t even  venture a name for the device used there. So this is still kind of just trial-and-error  engineering. I’m sure I could spend hours trying  

[11:13] different configurations and improving this  demonstration. If you’re a grad student looking   for a thesis idea, I think pulser pumps  would make a pretty interesting project,   because I can see some applications  here. In fact, I’m not the only one.

[11:26] Hydraulic ram pumps are pretty popular  around the internet and in rural areas   that have abundant water but no electricity.  They were well known by the time Professor   Cáceres did his experiment in 1911. In  his paper, he said about the pulser pump:

[11:42] the advantage of eliminating valves entirely,  since it contains no moving solid parts. Doing   away with the ram strokes seems to remove  any source of fatigue in the pipes and,  

[11:55] of course, the very annoying noise that makes  the ram inapplicable near living quarters.” I can’t help but think back to him in his  lab, seeing the water spurt out from the top   of the discharge line for the first time.  You can tell his excitement in the paper:

[12:10] “Beyond its historical appeal, the idea has  real value for modern engineering. In cases   where efficiency is not critical, reviving  it could solve practical problems, using a   layout so simple that it is remarkable it has not  become common knowledge after several centuries.”

[12:27] I wonder if he would be a little disappointed  that the idea never really did catch on,   despite its novelty. But I still  think it’s pretty cool. And maybe   someone will see my demo working and try  it for themselves, carrying the ancient  

[12:40] idea forward for new applications. Thank you  for watching, and let me know what you think!