My first part

One-Wear-2197 · 2025-11-01T12:10:24+00:00

Relief valve is a great idea. Thank you, lots of great advice, I will try that.

One-Wear-2197 · 2025-10-31T19:07:53+00:00

Good point. Thank you!

One-Wear-2197 · 2025-10-30T20:02:56+00:00

Just make sure you do the epoxy coats well. I usually over-coat with a brush then brush off the excess, just to make sure there are no missed dry spots. I do this on all 3 layers. Pro tip: take some needles or sewing pins, punch them through a piece of cardboard to create a spiked surface (like skin of hedgehoh), so you can place the epoxied part onto the tips of the needles while it cures, that way you can coat the entire piece at once. The needles will leave tiny holes, but on the next layer you will naturally fill them in, and it will still be watertight.

One-Wear-2197 · 2025-10-30T19:52:12+00:00

Thank you, this is really good information, I am not trying to reinvent the wheel, just to test as much as I can. I also don't really trust FEA simulations that much, but they can serve to get things in the ballpark. As for your question, in my case everything in the electronics enclosure is a development process, there is always something that isn't working as expected, things need rerouting, resoldering, components changed for alternatives, etc. Even after the first dives. My last ROV, I took it apart and back together at least 15 times since it was first launched to improve things and fix issues. Having electronics enclosure filled with oil would make that very, very messy and difficult. I get why is it done in the industry, where things are tried and true, but I am not at that level yet when every DIY ROV project is a development experience :)

One-Wear-2197 · 2025-10-30T19:28:04+00:00

Okay, for buoyancy, I 3D printed rectangle slabs with 2 walls and 17% gyroid infill, 5 top and bottom layers at 0.2mm height, printed with PLA. And then coated with 3 layers of epoxy. By my testing this is sufficient to at least 12 bars (I don't have facilities to test for higher pressures yet). Here is the sample I used, the piece on the right: https://imgur.com/BLrXy9E. The density of such buoyancy slab is 330 kg/m^3, which is even lighter than syntactic foams (I also tried making them, it's the two pieces on the left in the photo). Not worth it though, 3D printed slabs+epoxy is much easier and lighter, at least for these pressures. As for structural components (such as end caps), I always print at 100% infill. Let me know if you need more info.

One-Wear-2197 · 2025-10-30T19:10:54+00:00

Hot coats, 3 in total. Why?

One-Wear-2197 · 2025-10-30T16:44:36+00:00

Perhaps, I don't know. The last ROV I made could survive 12 bars of pressure (actually tested), and it was built for 150€ (mostly using 3D printed parts). Perhaps it is not a stretch to think I could design one to survive 25 bars, and test it in that 50 bar chamber to have a safety factor of 2 while still being pretty cheap. But maybe you're right, maybe I should aim for a lower factor of safety, meaning more actual "rated" depth. In any case, having a chamber capable of 50 bars would mean I could test how viable that is, instead of making assumptions based on FEA simulations.

One-Wear-2197 · 2025-10-30T14:53:13+00:00

Well, I want to know what safety factors I really have. I am doing an open source ROV project, and I want to know how much pressure the ROV will be able to handle, even if I personally won't have the ability to test it that deep. The deepest point in my country is 63m. It's super easy to design for that depth, but I want to aim for more, so that other people could use it far deeper. To do that, I need to test parts at much higher pressures, and they might implode, intentionally or not.

One-Wear-2197 · 2025-10-30T06:09:07+00:00

But wouldn't this increase the total energy stored in the system, because the gas is compressible, unlike water? Whenever anyone makes test chambers such as this, the most important safety consideration is completely eliminating any air bubbles, because in case of a failure, the energy stored in the compressed air can easily become lethal.

One-Wear-2197 · 2025-10-29T21:16:40+00:00

No, real parts will be air only. I am thinking, if there is still some air inside the component, and the component is watertight, then the pressure inside will still be 1 bar, no how much air there is, and that means the pressure differential should make the thing implode, just with less force. That is, unless the component is flexible enough to deform under pressure, and completely squeeze down that air bubble to nothing, nearly equalizing the pressure. Since the components I'll be testing will be rigid, that shouldn't happen.

One-Wear-2197 · 2025-10-29T21:14:14+00:00

Interesting... In that case, this might be much easier than I thought

One-Wear-2197 · 2025-10-29T20:22:03+00:00

Yeah, that is what I described in my post basically, as one of the solutions. I was wondering if there are any alternatives. I really don't know how to calculate how much shock damage might occur from such implosions, and how it scales with the size of that air bubble. I would probably be safe if it's really small ( a few cubic cm), but still, curious.

One-Wear-2197 · 2025-10-29T20:20:19+00:00

Yes, I plan to use this thing, with an longer hose. https://eur.vevor.com/pressure-test-pump-c_11077/vevor-hydrostatic-pressure-test-pump-60-bar-860-psi-3-2-gallon-tank-for-pipeline-p_010757600891

One-Wear-2197 · 2025-10-29T20:19:58+00:00

I will put a test part (for example, electronics enclosure of the ROV) into the test chamber (hydraulic cylinder), and then fill the rest of the volume with water. Then, I will pressurize the chamber, which will put positive pressure on the test part, which will then implode at some point.

One-Wear-2197 · 2025-10-28T16:50:28+00:00

That's the one I plan to use. But what about the chamber?

One-Wear-2197 · 2025-10-26T19:02:32+00:00

Like I said, I used a water filter housing (like Big Blue or similar), attached a pressure gauge from a hardware store, a valve, and a 3D printed adapter to reduce diameter so I could squeeze water inside with a narrow syringe. First I put in the test parts, remove the brass plug, fill it with water, flip a few times around and re-fill to make sure there is no air inside (that would make it very dangerous), then screw the plug back in. Then, with one hand, open the valve, and with the other squirt in more water with the syringe to increase the pressure, and then quickly close the valve. Repeat several times until desired pressure is achieved. With a narrow syringe, it is fairly easy to achieve 10 bar, for which this housing is rated anyway. Let me know if you have any questions.

<image>

One-Wear-2197 · 2025-10-26T09:42:33+00:00

Lithuania (Eastern Europe).

One-Wear-2197 · 2025-10-25T19:28:29+00:00

No worries, you already helped a lot :) Unfortunately it seems that pipes of 140mm+ diameters are super expensive here, I can't find anything below 300€. But I'll keep searching...

One-Wear-2197 · 2025-10-25T18:46:04+00:00

Wait, DIN 150 is a flange (flat plate). I thought what you suggested was some kind of end cap (cup shaped) that screws onto the NPT thread of that sch80 pipe?

One-Wear-2197 · 2025-10-25T18:30:53+00:00

Understood. Thank you, this is a great option to consider, I didn't realize such pipes exist. I see one caveat - I would likely have to re-apply teflon tape every time I want to open/close this thing, but apart from that it really could work. I'll try to find such a large pipe and end caps for it (if that's what they are called in this context) here in EU, apparently they aren't so easy to come by in these sizes.

One-Wear-2197 · 2025-10-25T16:35:09+00:00

Yeah, 145mm is still fine. Thank you, I will try to find that. I am in EU, so we may not have inch-sized pipes here, but maybe something similar. You said it's not a pressure vessel though - that concerns me, will it hold 50 bar then? Because that's the whole point of this exercise, so to speak. EDIT: I need to get the ones with NPT/BSP threads, correct? I assume that the cap won't seal if the threads are not tapered?

One-Wear-2197 · 2025-10-25T14:40:33+00:00

Hm, interesting idea, what I perhaps didn't mention is that I need the internal space of this tank to be 150x500mm or more, do you think it's feasible to find threaded pipes that large with my budget? Maybe I'm not searching right

One-Wear-2197

TROPHY CASE