Fluid Bridge Rectifier




This project combines woodwork and hydraulics to act as an analogy for a fairly basic, though incredibly useful array of electronic components known as a bridge rectifier.

A bridge rectifier is an electronic component that converts AC current into DC current, and comprises of 4 diodes in specific orientations to ensure the output current only flows in one direction regardless of which way the input is flowing at any given time.

Since the flow of electricity is difficult to visualise in the real world, explanations of how bridge rectifiers work are best suited to diagrams and videos, but this project is intended to provide a physical object for ease of understanding the concept.


  • Approx. 1m x 0.5m of plywood / MDF (9-18mm ideally)
  • Circular saw (Though still possible with a hand saw)
  • Drill and spade bits
  • Wood glue
  • 1m length of 16mm OD, 10mm ID tubing
  • 4x 3-way 16mm OD connectors
  • 4x one-way valves (Check valves)
  • 2x syringes
  • 4x 10mm hosetail connectors with 1/4" BSP thread
  • Flow indicator with 1/4" BSP threads

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Step 1: Making the Box

I created a digital sketch of the way all the components would fit into a wooden frame, and cut them out using a circular saw. The size was mainly determined by the tightest curvature radius of the tubing that I could achieve without it kinking, and the height was decided by the thickness of the syringes (Plus some extra for rigidity when drilling the holes later.

The frame was cut at 45° angles for maximum gluing surface area, and I cut a 3mm deep, 3mm high channel through all outer walls for a sheet of acrylic to go after (Thus converting it to a display case). The central divider was cut to the same height as the position of the recesses, so the acrylic panel would slide over the top of it.

Once glued together, I drilled holes through the bottom frame, centre divide and the two squares to provide a mounting solution for the syringes. It was necessary to remove the top of the holes in the divide since I couldn't mount the syringes after gluing the frame together.

Step 2: Test Fitting the Tubing

The tolerance of the tubing lengths had to be kept to a minimum for a couple of reasons: Firstly, even being a couple of mm out could make the difference between not making a proper seal with O-ring in the 3-way splitters due to being too short, or being too long and kinkind due to having to accommodate the extra length. Secondly, the first 8 pieces I cut (2 either side of the 4 one-way valves) used up over half of the 1m tube I had ordered, so it may be wiser to order longer lengths.

The two sections in the middle that fitted either side of the flow meter were the only others that had to be an exact measurement, which I couldn't determine until I had done a test assembly of the splitters, flow meter and hosetail connectors. When the latter finally arrived (Due to lost shipments and BSPT fittings incorrectly advertised as BSP!) I cut the two to length, which left around 40cm to divide between both syringes.

Thankfully I had accounted for a little bit of extra slack in the right hand tube due to the two tight bends it would have to make, so 100cm was just barely enough for the whole tubing run.

Step 3: Painting & Details

With all the test fitting complete, I removed the internal components and sanded down any sharp edges to give everything a smoother feel. A couple of areas needed filler, so I spread a thin layer of car body filler along the plywood edges as well as any voids. For a clean look, I gave the whole thing a couple of coats of white acrylic paint (Sponged on to try and hide some of the wood grain) and finished it with a gloss varnish.

I wanted to add some details to denote the one way valves acting as diodes, as well as a name plate to "title" the whole project, so I used a mini laser engraver to etch onto some small 20mm wide offcuts of 3mm ply. The title plate was 20cm long, so I tried to carefully align the engravings after splitting the image into 5 separate sections which was somewhat successful.

Step 4: Final Product

Despite a worrying moment where it seemed like the whole thing wouldn't actually work (Two of the valves were facing the wrong way!) the finished project worked perfectly.

I will eventually wall mount the box since it has an interesting visual appeal in itself, even if it's difficult to demonstrate its functions in such a location.

Here is a video showing the fluid bridge rectifier in action!

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    11 Discussions


    9 days ago

    It is a great innovation and probably something you can't buy. I've included a similar demo that I used when teaching analog electronics. I added a simulated capacitor (bottle) and resistor (needle valve). My students simulated and implemented bridge rectifier circuits but THEY said that playing around with my pneumatic model was the best way to learn. I also connected pressure sensors to the setup that produced graphs that were very similar to the waves from electronic rectification and smoothing.

    1 reply

    That's a great demonstration! I couldn't get the flow meter to work with the relatively small volumes of air (Before filling the system with water) but larger volumes and narrower tubes would help. Using a bottle as a pneumatic capacitor is a great idea!

    I wish I'd been introduced to demonstrations like yours when I was younger. Not only do they do a much better job at involving you, but they also make it easier to understand the reason why things work, rather than just the fact that they do!


    10 days ago

    Building on DoctorYoda's comment, an even more informative change might be to have one of those rotating indicators in series with each of the one-way valves.

    1 reply
    Shadow Of IntentOldSkiBum

    Reply 9 days ago

    That's not a bad idea, definitely worth considering for a larger build.

    This setup was optimised for for cost and space so it would have to be about 10% taller and wider to accommodate an additional 4 flow meters, plus it would have doubled the price what with even the cheapest flow meters being about £3 - 4 (I only spent around £12 - £15 on the tubing, syringes, connectors, valves and flow meter since I already had the wood offcuts and acrylic).

    The flow meter kind of represents the "load" on the DC side, so it might be a bit confusing to have one in series with each "diode". An ideal solution that comes to mind (If such a thing exists) would be valves that show whether they are in an open or closed state, perhaps by having a coloured sleeve that is exposed when the valve core slides open, similar to the pressure indicator tyre caps you can get!


    10 days ago

    Nice work, I really like it! One improvement idea: a number of small, colored particles (like bits of plastic) could be introduced into the water, showing the movement of charge carriers in the wire too.

    2 replies
    Shadow Of IntentDoctorYoda

    Reply 9 days ago

    Thank you! I did briefly mention adding pearlescent pigment in the video (It works very well in custom PC water cooling loops for showing the flow rate / direction) although it doesn't always show up as well on cameras since the particles / patterns are often too small to make out in detail.

    I did consider the idea of tiny plastic pieces as they'd make a better analogy for electrons, but I felt like they might cause issues with the one way valves, potentially causing them to stick open

    Alex in NZ

    10 days ago

    I remember when a friend of mine (hello DH!) showed me the bridge rectifier that he had invented. Even though they weren't the first person to invent it, it totally blew my mind!
    Thank you for sharing another new way of doing it :-)

    1 reply
    Shadow Of IntentAlex in NZ

    Reply 9 days ago

    Thanks! I was always fascinated by interactive exhibits at science museums as a child, so it's been great fun to make something that visualises electronics in another form!


    10 days ago

    I like it... a great teaching aid!


    11 days ago

    Although I don't know any practical application for this either, T think it looks really cool and might be good as a classroom demonstration object. :)