DIY Fish Decompression Chamber

[JaredWaites]

I'd like to make a mini hyperbaric out of large 10"-12" PVC Schedule 80, its rated for operating at 140 PSI, and it won't nearly be getting to 120 on most occassions.

It has a minimum bursting pressure of 790 PSI. So I think it would be safe to run it a little higher than 140 PSI although there is no need to.

Anyway so I'm curious if anyone has any good ideas...I plan to use a threaded cap on one end to fill with the saltwater, place the fish inside, replace cap. Then pressurize the unit using a bike pump or small 12V compressor.

What do you think? Any idea's?

- Jared

 

[mts0628]

Hey Jared:

Well, using 120 psi, that's about 236 fsw. So, now my question is why are you doing this? If it is to bring fish to the surface from a depth, please realize that unlike humans, when fish come up too quickly for them, that resuscitation is unlikely and really, strange when you think about it. This is not to say that it hasn't been done before. I mean, who would have thought of putting snakes in a pressure chamber? But then again, please realize the time era and context on which JS Haldane was doing his work.

As far as your fish, the trick is to bring them up slowly. I do not have much experience with this, as I only take what I eat and I do not collect fish from their habitat for show. I was with a guy who wanted to get a few unique fish and while he caught a few, most of them died on the way to the surface and we were conservative on out ascent profile. I think the biggest problem is with their swim bladders but I am not sure.

And finally, compressed gas is dangerous (DUH!) but recognize that just because the PVC tube is rated, what about the additional components and their attachment (via glue or threading)? Looking at most hyperbaric chambers, the ends are domed or rounded. This design is superior but not practical for the DIY'er.

An alternative would be to make a pressure chamber out of an old aluminum 80 [cuft] scuba tank. My good SB buddy 350xfire had a thread on making his. A lot of good scoop about acrylic and sealing (o-rings versus gaskets) too. And filling the chamber/tank with water will reduce the hazard but not eliminate it.

I hope this helps and no matter what, no mad scientist experiments. Good luck!

With kind regards,
Thomas

 

[miketsp]

I'd like to make a mini hyperbaric out of large 10"-12" PVC Schedule 80, its rated for operating at 140 PSI, and it won't nearly be getting to 120 on most occassions.

It has a minimum bursting pressure of 790 PSI. So I think it would be safe to run it a little higher than 140 PSI although there is no need to.

Anyway so I'm curious if anyone has any good ideas...I plan to use a threaded cap on one end to fill with the saltwater, place the fish inside, replace cap. Then pressurize the unit using a bike pump or small 12V compressor.

What do you think? Any idea's?

- Jared

12" cylindrical pvc tube can resist a significant pressure.
The problem is the flat caps.
A few years ago I was building a UW housing for a film camera and when I started getting into the formulae for flat pressure resisting windows (there's a surprising amount of literature on the Internet for both aeronautical applications and DIY submarines) you find that once you get above 5 or 6" diameter, the wall thicknesses get ridiculous.
As mentioned already by another poster at 12" you would need to mold domes and this starts getting a little tricky, although not impossible.
The other issue is how do you intend to renovate the air inside the chamber to ensure an O2 supply for the fish. Also bicycle pumps and 12V pumps won't exactly give you a clean compressed air - the air will be heavily oil laden. Your best method to get clean compressed air would be a scuba tank and a regulator. Equip the chamber with an over-pressure valve, preferably 2 at different settings - one to allow you to get a flow-through and renovate the air and the second at a higher setting to act as a safety valve.
If you plan to put fish inside, it would of course be recommended to have a viewing panel to observe when they're all dead and your experiment has ended.

This is all purely academic as I can't really see the practical use for your application.

 

[JaredWaites]

Hey Jared:

Well, using 120 psi, that's about 236 fsw. So, now my question is why are you doing this? If it is to bring fish to the surface from a depth, please realize that unlike humans, when fish come up too quickly for them, that resuscitation is unlikely and really, strange when you think about it. This is not to say that it hasn't been done before. I mean, who would have thought of putting snakes in a pressure chamber? But then again, please realize the time era and context on which JS Haldane was doing his work.

As far as your fish, the trick is to bring them up slowly. I do not have much experience with this, as I only take what I eat and I do not collect fish from their habitat for show. I was with a guy who wanted to get a few unique fish and while he caught a few, most of them died on the way to the surface and we were conservative on out ascent profile. I think the biggest problem is with their swim bladders but I am not sure.

And finally, compressed gas is dangerous (DUH!) but recognize that just because the PVC tube is rated, what about the additional components and their attachment (via glue or threading)? Looking at most hyperbaric chambers, the ends are domed or rounded. This design is superior but not practical for the DIY'er.

An alternative would be to make a pressure chamber out of an old aluminum 80 [cuft] scuba tank. My good SB buddy 350xfire had a thread on making his. A lot of good scoop about acrylic and sealing (o-rings versus gaskets) too. And filling the chamber/tank with water will reduce the hazard but not eliminate it.

I hope this helps and no matter what, no mad scientist experiments. Good luck!

With kind regards,
Thomas

Yeah the problem with bringing the fish up really slow to acclimate them and let their swim bladders adjust, in order to properly do this, it must be done over the course of a few hours from a hundred or so feet...

I've successfully captured a few fish and used a small syringe needle to vent their swim bladder and the fish have done great...but I'd like to see how gradually bringing them up and then using the chamber to recompress them to their depth and slowly adjust the pressure, to the surrounding area. The problem with bringing a fish up from major depth is they cannot release the gases quick enough from their bodies and actually their swim bladder expands and forces its way out of their mouth and their eyes can even 'pop' and bulge out. At that point they are normally beyond return...I'm trying to prevent this so we can get a more ethical successful method to capture tropical fish. The majority of saltwater fish kept in my hobby are all wild caught. With efforts for breeding aquaculture species, there are still some species that would benefit from this as there are also a lot of deaths associated with the shipping and importing of tropical fish and even capturing. A lot of capture methods use Cyanide to force fish and inverts from coral heads and reefs.

12" cylindrical pvc tube can resist a significant pressure.
The problem is the flat caps.
A few years ago I was building a UW housing for a film camera and when I started getting into the formulae for flat pressure resisting windows (there's a surprising amount of literature on the Internet for both aeronautical applications and DIY submarines) you find that once you get above 5 or 6" diameter, the wall thicknesses get ridiculous.
As mentioned already by another poster at 12" you would need to mold domes and this starts getting a little tricky, although not impossible.
The other issue is how do you intend to renovate the air inside the chamber to ensure an O2 supply for the fish. Also bicycle pumps and 12V pumps won't exactly give you a clean compressed air - the air will be heavily oil laden. Your best method to get clean compressed air would be a scuba tank and a regulator. Equip the chamber with an over-pressure valve, preferably 2 at different settings - one to allow you to get a flow-through and renovate the air and the second at a higher setting to act as a safety valve.
If you plan to put fish inside, it would of course be recommended to have a viewing panel to observe when they're all dead and your experiment has ended.

This is all purely academic as I can't really see the practical use for your application.

Let me further explain my needs for a system like this, mainly to be used for research of marine specimens for local aquariums and even local FWC has shown an interest. I have no plans to sell such plans to make this unit, or the unit itself. I'd like to pioneer a new method for treating captured fish for the ornamental tropical fish industry. Its a multimillion if not near billion dollar world wide industry. I've been collecting tropicals for years and have actually used a setup as mentioned that used a step type bicycle air pump. Its not that its not possible, there are just a few problems to which I plan to overcome within the first or second model of this unit. I don't have to worry about the oxygen supply as the oxygen in the water along with the small amount of surface air compressed will provide more than enough oxygen for a few hours of treatment especially if the air that is introduced is compressed medical oxygen. Everyday hundreds of fresh and saltwater fish are shipped overnight and some even 2-day air throughout the United States and they live just fine so I'm not worried about the oxygen content of the water, although that's easily monitored.

A viewing window will not be necessary as it will just complicate the mess....although I can easily use a thick walled cast acrylic tube and use a schedule 80 end cap along with a schedule 80 threaded male adapter and use a threaded plug to seal the hole.

 

[mts0628]

...
As mentioned already by another poster at 12" you would need to mold domes and this starts getting a little tricky, although not impossible.
The other issue is how do you intend to renovate the air inside the chamber to ensure an O2 supply for the fish. Also bicycle pumps and 12V pumps won't exactly give you a clean compressed air - the air will be heavily oil laden. Your best method to get clean compressed air would be a scuba tank and a regulator...
If you plan to put fish inside, it would of course be recommended to have a viewing panel to observe when they're all dead and your experiment has ended...

Mike brought up great points. I am envisioning Mythbusters and vacuum forming for the domes but at the crazy thicknesses, DIY becomes PITA I think and then attaching them securely to the housing, GRRRR! Also, I never would have considered the air and recirculation issues (but then again, I never thought about this application).

Let me further explain my needs for a system like this, mainly to be used for research of marine specimens for local aquariums and even local FWC has shown an interest...A viewing window will not be necessary as it will just complicate the mess....although I can easily use a thick walled cast acrylic tube and use a schedule 80 end cap along with a schedule 80 threaded male adapter and use a threaded plug to seal the hole.

Uh, oh yeah. "I see!" said the blind man. So you do have a genuine intended purpose for this thing. Neat. I still am kinda' skeptical on the practicality of the system but if it will work for you, great!

On the chamber note, people safety is always first. Make a solid and safe pressure chamber with an OPV/drain first and then add the amenities. While you discount a viewing port, I think it would be simpler to seal and more reliable to use for your intended purpose.

Well, good luck with your building and please post pictures when you complete your project.

With kind regards,
Thomas

 

[antero]

Can't you just build a volume w/required pressure differential strength and make a bleed valve. You put a poor animal into the chamber at depth. Screw the bleeder and surface w/it. Then slowly release and drain watching the pressure gauge? Or am i missing something?

Would you like to try it first on cats? I have one to spare but you will need a scooter size chamber

 

[JaredWaites]

The purpose is to collect the fish and get out of the water without long decompression times. Now the local harvesters and locals in other countries that rely on the ornamental fish business are killing hundreds of thousands of fish by using cruel collection methods and using outdated collection techniques. Although I'm not discrediting your idea, I don't think its feasible to carry a length of 2'-3' PVC diving, along with clear catch nets and even small 2-3 foot cast nets. That's a lot more gear to bring with you and keep up with at depth. It takes a while to decompress fish this is the problem with common techniques to collect fish now, they use nets, transfer them to holding vessels and the divers surface, every hour or two they raise the vessels higher in the water column. But this can lead to a long day of decompression.

The only problem with a viewing port or something in this nature is that if I use a PVC pressure vessel then I would have to find a clear thick acrylic cap. It can be done but I don't know if its worth the money, or even if they make an 10"-12" end cap in cast acrylic. I'm over 100% positive that a pressure vessel made of PVC will hold the PSI that I'm looking at, including the gauges and other features.

A lot of this project will mainly benefit research labs, such as the Gulf Coast Marine Specimen Laboratory (GCMSL.org - currently offline) and a few other places that I'm involved with that do marine specimen research, including coral disease, RTN, etc.

 

[DIWdiver]

Could you perhaps provide a small viewing port at each end so the size wouldn't be prohibitive, and you could see the whole vessel?
D

 

[diverdown78]

I'd like to make a mini hyperbaric out of large 10"-12" PVC Schedule 80, its rated for operating at 140 PSI, and it won't nearly be getting to 120 on most occassions.

It has a minimum bursting pressure of 790 PSI. So I think it would be safe to run it a little higher than 140 PSI although there is no need to.

Anyway so I'm curious if anyone has any good ideas...I plan to use a threaded cap on one end to fill with the saltwater, place the fish inside, replace cap. Then pressurize the unit using a bike pump or small 12V compressor.

What do you think? Any idea's?

- Jared

iv put alot of pipe together for columbia gas an i suggest you use polyehylene pipe use for medium pressure gas

 

[smellzlikefish]

Hi Jared;

I've worked in a couple of public aquariums and have been on a number of collecting trips with various aquarium personnel and professional fish collectors. My last aquarium had a specimen (only one of its kind in captivity) that had been brought up from ~300 feet and needled. I think your idea is a great one that has potential to alleviate the stresses of capture on the fish brought from depth and may enable even deeper species to be brought up, for better or worse. I never did trust the needling method, even if the fish appeared fine afterwards. I think the PVC should maintain the ambient pressure at depth negating the need for a bicycle pump or compressor. Simply take your octo and put a little air in the chamber at depth. I might swap the pump out for a pressure gauge and slow release valve like they have on the pressure pots at SCUBA equipment repair shops. The idea is simple enough, I might just borrow it and try it on my own, if you don't mind! I see DIY fish recompression tables in the future...