Functional SCUBA Low Pressure Demand Regulator v3.6 by Biketool

Last crawled date: 2 years, 12 months ago

This is what 3D modeling and 3D print rapid prototyping excels at, We were able to take some used bicycle tubes, gas hose, and a cut supermarket snorkel to make a functional if crude prototype of an idea based upon a 20 year old memory, and we did it all in the same afternoon. From the press this project has since attracted we reasonably believe this may be the first ever amateur designed and built functional 3D printed low pressure regulator.
WARNING!! I DO NOT GIVE PERMISSION FOR HUMAN OR ANIMAL USE!!! These terms affect the user license and is in addition to and overriding to any terms of the use license. The permissive license only covers the digital files, any real things printed or made in any other way are your own responsibility and may not be used for human or animal purposes or any use which could in any way confer liability to myself my employer or anyone else other than the end users. Only people over the legal age of consent and contractual obligation in both my and their jurisdictions and any jurisdictions of use or legal responsibility may use these files. What I am saying simply is these files if somehow used to make real things are too dangerous for ordinary people for so many reasons do not imperil lives or property, there is no point suing anyone if you did something illegal like pirating these digital files and knowledge for purposes not intended. This is a litigious and ignorant world, the digital files are free-libre but there are limits on using the 3D models to make real world objects for prohibited uses
OpenSCAD files for an easy to source and inexpensive DIY demand low pressure regulator I intend for my personal demonstration use with 120PSI filled 2l carbonated softdrink bottles or a long hose and a home workshop air tank/compressor. Regulator valve lever is included with the inner_mechanism file until v3. Just print this and acquire a blown bicycle tire of sufficient diameter to scavenge the valve and rubber and some wood screws. A supermarket kiddy pool snorkel is an easy way to find a mouthpiece just snip it to length and zip-tie on. The Schrader valve pin pusher on the pivot lever requires some trimming to function correctly. May require sealing the printed body, as my printed walls were so porous that the regulator would flood with water when inspiring, sealing fixed the issue.
Needs a round rubber diaphragm to press the demand lever(bicycle inner-tube rubber) and a bicycle tire Shrader valve to actually do the precision work of the demand valve, a pin for the regulator valve lever, a scuba mouthpiece (or hack one off of a supermarket snorkel), as well as a bit more rubber innertube scrap for a flapper valve for the exhale port. V2.0 files are printed and tested, the v3.x stuff looks nicer,stronger, and better designed IMHO but is vaporware for now and may require a wider sheet of rubber, comment if you do test them. Just to be clear the only precision part in this regulator is a factory made Schrader valve, everything else is just there to press that pin to release breathing air or to valve out any exhaust air and water in the regulator at exhale.
To make a demo soda bottle pressure vessel I removed the valve core and left the rubber round skirt intact to make the seal, I had a 50% success rate making the seal actually hold so I suggest grabbing a few if possible, to this I attached one end of the air hose. At the regulator end I threaded the intact and functional but with circular tube side skirt trimmed off valve stem into the valve block until I could activate the schrader valve by pushing the purge button(hole in regulator where you can push the diaphragm) then I valved out the air, once empty I loosened the clamp and adjusted the hose as a stop collar so I could easily unscrew the valve block and the bottle could be pressurized with a tire pump and have it stop at the correct position.
I added a terrible laptop touchpad freehand graphic to help visualize how simple this and most second stage regulators are. Do you know how hard it is to draw an arrow with a touchpad?!
I only give permissive license to take this these files for academic study and educational demonstration models on how a second stage demand regulator works, I do not give permission to print or use as SCUBA systems or any use for humans or animals. Our lungs are surprisingly fragile and drowning, air embolism, or lung injury are actually pretty easy when dealing with compressed air and depth, especially to untrained divers so don't use this it is a science demo not a real regulator for human use. This is somewhat inspired by an old Soviet rebreather oxygen demand add valve design which used a schrader valve which I liked because you can get Schrader valves anywhere, I seem to remember some Scott Aerospace fire/mine SCBAs using a schrader too. Beyond using a schrader valve, and a lever actuated by a diaphragm it is a clean sheet design without any reference; water goes down, air goes up, pressure differential pushes diaphragms, flapper valves vent only one way, levers push pins, open valves vent higher pressure. Despite linking to a ScubaPro youtube video to show how a commercial regulator is assembled and works this design has nothing to do with ScubaPro and is not inspired in any way by any of their designs, it was added after the fact for educational purposes.
If you need a real acquire-to-use second stage regulator for a scuba or vehicle/aircraft submerged water escape rig buying used and getting serviced is so cheap and you will almost certainly like the results better in any case considering how much effort is required to trip the schrader valve, not to mention you do not have my permission to use this regulator for those purposes. I do very strongly endorse having a 100% separate from your SCUBA spare-air type rig for a rush to the surface should you experience a main equipment failure, also for people piloting aircraft over water in case of ditching and submerged escape(in addition to life preserver, raft, EPIRB, radio, and survival kit) or even 4x4ing where there is a possibility that the vehicle could end up submerged. This is not the basis for that equipment though. I use a regular SpareAir for SCUBA diving and keep a Navy surplus Aqualung SEA when piloting small aircraft over water.
Demand valves and positive pressure demand valves are also used in firefighting, environmental suit, and mining SCBA rigs, demand valve oxygen add is also used in closed loop C02 scrubbing rigs in space suits, escape rigs, and rebreather diving systems. Demand valves are found in many gas and liquid systems, you could also use this to simply measure or switch based on pressure or vacuum rather than a adding Schrader valve. Use it for any other quick and dirty same day proof of concept reduction to practice as long as nobody threatens anyone's life safety or property with it.
The mechanism is explained here:https://en.wikipedia.org/wiki/Diving_regulator
andhttps://en.wikipedia.org/wiki/Schrader_valve
and
start at 7:00 for the second stage https://www.youtube.com/watch?v=dEaRXTjV9qM
The regulator works like this:
Sucking air from the mouthpiece drops pressure in the sealed regulator body,
the air or water outside pushes inwards the rubber diaphragm which is sealed against the valve block body
The pressure difference also presses the flapper exhaust valve shut
The diaphragm pushes against the pusher disk which centers diaphragm push pressure against
the valve lever
the valve lever is pushed backwards
pivots and
the push pin on the lever pushes against the Schrader valve pin
the Schrader valve opens
air enters the regulator through the schrader valve from
the air hose or tank for as long as there is suction
the entering air balances the suction until
the lungs fill
the suction stops,
inside and outside pressure are again balanced
the diaphragm returns to normal position and
the lever returns to a normal position
the valve closes
then the diver exhales
the exhaled air along with any water in the regulator body exits through the one way flapper valve over the vent
the inhale exhale cycle repeats until the compressed air supply is exhausted
You can also push through the hole in the front cover exposing the rubber diaphragm to purge your regulator, though with the carbonated beverage bottle setup it is not like you have to air to waste with a purge, but if you are making a demo which sources from an air tank or compressed air system it is an easy way to functionally demonstrate without sucking directly on the regulator.
Edits
7-18, upgraded everything to 2.0 added assembly screw holes did some test prints and made the valve block work though requires some trim on the pin pusher, actually activates the pin vs v1, bicycle tire Schrader valve screws tight into valve block now. I hope to do a v3 with a m2 screw rather than plastic on the lever to give better adjustability. Added pusher disk for between diaphragm and valve lever and to make sucking air easier.
7-20, edited the back cover again so that you just put a membrane of rubber over the valve&body and sandwich it with the mouthpiece part. It works when tested but leaks on inspiration and needs a better seal at the back and possibly around the front diaphragm. I did a bead of chewing gum sandwiched between the body and mouthpiece opening in keeping with the available at a supermarket rules. Everything secured with round head wood screws.
7-21, Learned something about pneumatics and FDM printing, it turns out that the body, ABS printed at 100%, 0.5mm layers, 250C is so porous that it requires sealing to prevent water entering the regulator. I am soaking some acetone into the walls to see if that is sufficient, then had to use an ABS acetone paste and caulked the inner walls with that. System is now well sealed, trimmed the diaphragm to fit inside the outer protective cap so it is easier to re-assemble, going to bake at 60c to dive off the acetone. once the acetone is gone I think I can call this finished. Tested in a pool, it releases a bit slowly from a 100psi soda bottle, certainly not the familiar hard rushing air blast from a real high pressure SCUBA rig but works as a demo, the sealing held and the exhaust valve works too, the regulator stays dry between between the sealing and purging any leak water on exhale.
8-3, v3.0 Enlarged the screw holes and made thick housings for them as well as moving them outwards to keep the main wall inner integrity and keep it smooth to make sealing easier. added O-ring groove around mouthpiece mating area and six screw holes use with rubber washers or o-rings. Left v2.0 files as they have been field tested successfully, v2.0 also works with simple wood screws.
8-3.2 Did a v3.5 body and split off the valve activator arm as it's own file and replace the plastic valve pusher nub with a machine screw.
8-3.3 v3.6 mod on the valve block body assembly, just added a stop block to prevent the valve activator from bending or breaking if pushed too hard, not likely from sucking against the diaphragm but makes me feel better when pushing the purge valve.
A cheap demo SCUBA tank:
We neutralized the buoyancy of the ~1.5l softdrink bottle air tank with a 2kg sledgehammer head, so obviously it held 2l of air displacing 2l or 2kg of water; buoyancy was perfectly neutral and the weighted bottle would hang in the water wherever placed. the tank was made by wrapping a 1.5l carbonated drink bottle with 3M nylon strapping tape. we drilled the cap and removed the seal disk. We cut the schrader valve and the rubber disc where it attaches to the innertube from a bicycle innertube and removed the valve core. The valve stem was pushed through the hole in the bottle cap until the disc was forward of the cap threads, then the bottle cap was screwed down seating the rubber disc against the bottle opening. Rubber gas hose was hose clamped onto the protruding schrader valve stem. A second bicycle valve stem with the attachment disc trimmed off was hose clamped at the end of the hose, this one with the schrader valve core intact. the system is filled through the functional schrader valve at the end of the hose with a bicycle pump to 100psi; once full the valve is screwed into the regulator until air is heard escaping, then back off unscrewing until the air is no longer heard. We moved the hose to the point where the threads had a bit of friction when fully tightened speeding assembly.
Again I must stress that even with these proposed upgrades this regulator was designed as an educational demo and I would not want to hear of it being used to dive, it is not designed or tested for use at depth. I have no idea what the actual pressure rating for a cheap bicycle schrader valve is, or gas hose but I would not imagine anyone designing over 150psi/20bar. Be smart only use diving life support gear from a trusted modern manufacturer source with a known and logbooked history, your life depends on it. Also take a SCUBA refresher class from a real instructor on a regular basis to shake off your bad, dangerous, or deadly habits.
Perhaps posting this thing will inspire a trained, experienced, and certified engineer who is willing to take on the perilous legal responsibility which many countries put onto makers to review, test, fork, and release this design as certified or endorsed as safe to dive; until then I am the only person with permission to print for human diving purposes if that even turns out to be legal, all others are pirating my design if they dive or even breathe with it or use it in a design which could ever be used or accessed by a human or animal. For you all this is a functional demonstrator model no more usable for real world application than the printable jet engine models found on thingiverse. I simply do not have the deep pockets or insurance coverage to accept the liability to ever release this as a working device.
Daydreaming/sketch notes:
It would be fun to find a CO2 tank for a soda fountain and fill it using a scavenged refrigerator pump with an air filter on the intake side. Most can produce 600-800psi and that is about the typical room temp pressure of compressed CO2 so is a good match for available hardware. This would require a first stage regulator to take tank pressure down to about 200PSI for this regulator. Might print in PLA and do al lost PLA cast in brass and lathe/drill&tap to spec.
I might also modify a smaller seltzer maker CO2 bottle adding a first stage, on/off valve, gauge, and a fill port and carry it like a spare-air along with a regular dive rig for my own(and nobody else's) testing purposes at depth.
If I do that then we also need a pressure gauge, a depth gauge is easy marking a plastic tube with 1/2 way at 33ft or 10m 3/4 the way at 66ft/20m etc. and a luminous compass.
Of course these pressures get dangerous fast so perhaps better to stick with a commercial first stage.