Questions on a DIY project

[TMCR]

Ok I have a couple of questions. I am new to any scuba or breathing assisted type activities and I have a project that I am doing that I would like to verify some things and learn on others. My main questions are:

1. Mathematical calculation verification
2. Regulator Information

First, I would like to clarify a few things before presenting the design of the project. This project is only intended to give a set number of breaths to allow me to search a river bottom that averages 5 feet with one section that goes maybe 12-20 feet max. This is not intended to be a scuba tank in any way, just a device to give me a set number of breaths. Ok with that out of the way, now I can lay out the design. The "tank" will be made out of 2" pvc and have a total length (tentitively) of 74". Using elbows and tees I will have 3 sections @ 18" long and 2 @ 10", which will form a square with a post in the middle. There will be a filter at the the discharge port which the regulator will be hooked to. Filter medium will be a 13X dessicant sieve followed by activated charcoal. Tank will be filled to a maximum of 100 psi and more likely 80 psi (mathematical equations that follow will show 80 psi) for safety. Tank will be filled with a standard t handle bike pump (possibly with the same type of filter attached). Regulator will be a cheap $22 hooka regulator from amazon (to be posted below). All pipe will be covered with closed cell foam for additional impact resistance. Now for the first question. I want to make sure my air calculations are correct and that I am not missing anything.
Interior volume of tank: 3.81 liters
My calculation from the tank calculations on this site:
3.81L x. 03666 x 80psi / 14.7 = 0.7601339 ft³
Average human breath: .5 liters
5L = 0.0176573333607 ft³
0.7601339 ft³ / 0.0176573333607 ft³= 43.0491901. So my estimated amount of breaths I can take from this would be 43. This again is just an estimate. Are there any errors or additions to my calculations I may have missed? Now for the regulator. Here is the regulator I am thinking of getting for this: https://www.amazon.com/dp/B01AL6U

N22/ref=asc_df_B01AL6UN225247010/?tag=hyprod-20&creative=395033&creativeASIN=B01AL6UN22&linkCode=df0&hvadid=167139952559&hvpos=1o1&hvnetw=g&hvrand=7890581859452685895&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9029671&hvtargid=pla-311901231993.

It says a maximum of 145 psi, so I am assuming that I would have to adjust it down to 80 psi? Or will I not have to adjust it at all? Is there any danger of not adjusting it? Also, can someone explain how the regulator of this type takes the pressure down to a non dangerous level for breathing? It's hard for me to word this question correctly, but basically when breathing from a tank what psi of air is too much to try and breath in in one breath and how does the regulator prevent to high of a pressure from being inhaled? Just trying to get educated. I don't need to have this project done until next summer so I wish to learn as much as possible. Thanks and looking forward to talking with everybody.

 

[tbone1004]

holy sigfigs.....

I officially don't condone this idea for the record, but if I were to do it this is how I would.

ok, so you need to do the following "rough" math based on minutes not number of breaths.
.8cfm is about right. Then multiply that by 1.6ata based on your 20ft depth is about 1.3cfm

Your regulator needs a certain pressure to function. Hookah second stages are designed to run about 110psi, and typically are good for 3ata. At 3ata you can knock 30psi off so you need about 80psi feeding that second stage to make it happy.

If you want 1 minute of breathing at depth and have a 100psi limit, you need 20psi to equal 1.3cf and at 100psi, the total volume to be 5*1.3 or 6.5cf for a total internal volume of about .9cf or 27 liters.
That will give you somewhere around 15 breaths at "normal" breathing resistance. You can likely suck it down lower, but you will have increased work of breathing which is another safety issue.

If you feel that you can build something that is of similar volume and will safely hold 100psi, while also have a safe regulator attachment, they go for it. I would urge strongly against it. The cost/size/complexity/risk of this project does not balance out, especially compared to purchasing a small pony sized bottle or learning to freedive properly


My official recommendation. Learn to freedive.... You can stay down for about 2 minutes with not a whole lot of practice and 20ft is a cakewalk
If you want to breathe while down, just get a small AL19 or something and monkey dive it. Not really any more expensive, but a lot less risk for something to go seriously wrong

 

[northernone]

I like the level of understanding and thought you're putting into this project. Happy to help as it develops but I have a few cautions.

Building your own PVC pneumatic bomb concerns me. Homemade scuba tanks can be done but PVC is not the suitable material. If there is a defect or damage, it shatters into rather unpleasant shrapnel. I'm fortunate to be unscathed but I have a dog who would hide under the porch at the appearance of a pvc pipe for years following a certain diy project I was working on that sounds similar to yours in some ways.

If you read up on pulmonary embolisms and lung expansion injuries related to breathing compressed air at depth and get training for SCUBA diving safely I, for one, will be happy to help with your homebuild project.

At this point I do not feel comfortable in making suggestions towards the completion of something that can easily be fatal.

Enjoy the learning process!

Regards,
Cameron

 

[tbone1004]

another alternative is to purchase a spare air, and then have a large scuba tank on the surface that you can transfill into which is going to be super small, much safer, and realistically not cost that much more.
Your location isn't provided, but you can get a pair of used AL80's for about $200, and a spare air for about $200. $400 and you have something safe, more versatile, and MUCH smaller underwater than what you are proposing.

Spare Air also has a hand pump option which isn't cheap, but again, because you can get to 3000psi, you have a much smaller package, as well as it being a lot safer than a PVC bomb

 

[uncfnp]

another alternative is to purchase a spare air, and then have a large scuba tank on the surface that you can transfill into which is going to be super small, much safer, and realistically not cost that much more.
Your location isn't provided, but you can get a pair of used AL80's for about $200, and a spare air for about $200. $400 and you have something safe, more versatile, and MUCH smaller underwater than what you are proposing

This is exactly what I was thinking, after getting certified of course.

I don’t dive rivers but isn’t the risk of entanglement a concern?

 

[tbone1004]

This is exactly what I was thinking, after getting certified of course.

I don’t dive rivers but isn’t the risk of entanglement a concern?

it depends. I avoid river diving, but usually just strap a single on and go so I can stay down as long as I want. Entanglement with that limited of an air supply would certainly be a concern to me though, though the risk of entanglement is lowered without a big scuba tank. The OP's plan though has the downsides of both

 

[northernone]

This is exactly what I was thinking, after getting certified of course.

I don’t dive rivers but isn’t the risk of entanglement a concern?

Entanglement is significant... my worst was cutting myself out from the inside of a blanket caught in a submerged tree a temperamental current opened up to swallow me. Bicycles, twisted metal, fishing lines etc are everywhere in most populated areas.

Regards,
Cameron

 

[TMCR]

Ok sorry for the delay in responding. First thank you for the replies and for the additional calculations, those have helped immensely. Ok, I thought the pvc might be a bad idea but I like to explore all options. So I have switched my project to my second option. I work as a machinist and my shop does high pressure stuff (valves, chambers etc.) for the oil industry as well as many other industries. My work gave me one of the chambers we make that are rated for 3500psi, so this will now be the basis for my project. I know I know, many of you are thinking why didn't I start with this in the first place. For one With my projects I love to learn all I can and explore all options, and second, time money and energy. A few expenses related to this have changed. For one, apparently my work makes filters that are used by everyone including scuba customers, and they have offered to just make me one. We also make valves so a shutoff valve is an expense that I don't have. I will have to machine an adaptor for the first stage but that will be easy. To fill the tank, I will be trying to get a high pressure hand pump for air guns (they go up to 4500psi) to fill the tanks. With Christmas around the corner I may have to ask for a regulator set that I have my eye on. Thanks for helping me to learn. And keep the suggestions coming. Oh I forgot, the chamber when pressurized will give me 10 minutes of air, according to the calculation that was suggested above. Thanks again.

 

[tbone1004]

@TMCR make sure the chambers are rated to be fully submerged. Oftentimes the coating/hardware used isn't designed to go underwater.... Still unsure how you're coming out cheaper than a small scuba tank though once the fittings have been factored in, but nifty that you work for the guys making the filter housings though

 

[TMCR]

I asked my supervisor when I took it and he confirmed it would be fine. Hmmm, maybe I have missed a part or something. What is a good source for scuba tanks. Here is the list (tank wise at least of what I have or will have after machining the part my self :
.Tank (the above chamber)
. On/off valve
. Fill port
. Adaptor for the first stage
Oh I forgot all parts are either 303, 316, or 6061 aluminum.
Yeah it has been nice, they have been more than willing to help. Thanks for the reply.