Intro: 3D Printed 50psi Water Pressure Vessel
3D printed containers are not known, or probably not safe either, for holding water pressure. But I wanted an item I could use on a garden hose, and it should not excessively leak at 50psi. My first attempt, a year ago, sprayed water from every crevice, more of a fountain than holding pressure!
But printers have improved and I changed my printing method also. I decided to make a sphere and determine if it could hold 50psi without any active spray or leak.
Under the functional assumption I wish to put something inside of the vessel (my ultimate objective), the vessel must be printed in parts and then assembled. So I did this test run, printing a sphere, with a hose thread in and out on each end. The sphere printed as 2 hemispheres. Pressure beating surfaces will be coated, and the parts glued together.
My design approach is to print each part with the pressure bearing surface oriented upwards, such that the printer plastic would lay down and adhere as best as possible. So the sphere open upwards, and pipe fittings are vertical.
Step 1: PLA Printed Parts - PVC Glue the Hose Pipes
I printed in PLA material, for strength and holding its shape. Further all the parts have at least 3mm wall thickness, and *the printer is set for 100% fill* !!!
The hose in & out pipes have rims to grab on the inside of the hemispheres. The hemispheres have flat plate surfaces to match with the pipes. I used simple PVC (irrigation pipe) cement to attach the pipes. The water pressure will cause them to press against the hemisphere plate, so this glue is not load bearing.
Step 2: Use Polyurethane Coating on All Pressure Bearing Surfaces
I coated the inside of the hemispheres, and the inside of pipes, and the ends of the pipes, with polyurethane.
I used 3 coats, allowing each to dry.
I was careful not to get the polyurethane onto the snap-rim structure which will join the hemispheres together.
My design of the snap-rim proved to be quite snug and I had to really apply pressure to join the hemispheres together.
On my first attempt, I used the same PVC cement to join the hemispheres, and *it didn't work*. Under about 20 psi the hemispheres popped apart! This failure did not break the plastic, but opened at the snap-rim.
So I switched to Loctite Super Glue Ultra Gel, which is commonly recommended! I should have started with that. Applying a generous layer to the snap-rim, and then 10-15 lbs of force, the hemispheres joined.
Step 3: It Holds Pressure!
Warning: if 50 psi of water pressure suddenly pops open, the bits of plastic debris may be a hazard. Eye protection must be used when any pressure is applied.
In this photo you can see, after a minute or two, the pressure is at 55 psi, and barely a drip on the sidewalk!
I count this as a success!
Warning: to make a practical use of this design idea, destructive testing must be done, to determine the safety margin against the plastic flying apart!