Hi All and thanks to Zack for encouraging me to write this up.
To help us test new OpenCTDs without going several miles offshore, we developed a cheap, reliable, (mostly) safe pressure vessel to simulate 50m depth. The set up uses commercially available whole-home water filter housings, a cheap air compressor, and off-the-shelf pressure fittings. It fits anything that can go into a 4.5" by 20" cylinder. So far, we’ve pushed a couple dozen CTDs down to 50m or more.
There are some more intense stainless steel industrial water filter housings that are rated to 300psi which could conceivably get you down to a little more that 200m, but I haven’t had a chance to test those out, yet.
@estackpole may be able to give you some tips/lessons learned on building cost-effective hydrostatic test chambers that can go deeper, and how to keep them (mostly) safe as you do.
There are a couple of guys in Poland who run a website called CPSDrone who have done something similar. Might be interesting to compare notes with them. They offer plans for building a drone that can go down a couple of hundred meters (3D printed parts) as they did some testing using a homemade pressure chamber that looks similar to what you’ve constructed. Great work!! Ron