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Jan 22, 2019, 03:22 PM
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Idea

Air tank for airbrush


I got my self one cheap airbrush kit with a small compressor, you can get one for like 30$. I've made a cheap air tank for it with an Coke plastic bottle and I'm quite happy with it.
- http://store.piffa.net/gunpla/comp/

Specs are:
- 1.9atm max pressure
- 10 liter air per minute
- 1.6ampere 12v, so you can use it with a lipo 3s 2200mah in case (warning: no reverse current protection)

It's enough to keep my airbrush up to ~1.3 atm constant while painting and I usually can do with just 0.6-0.8atm.

As the air compressor is quite noisy I'm thinking about using a larger air tank, something like 5, 10 or even 20liters in order to keep the compressor turned off while I'm painting.

So I was thinking of using a plastic fuel tank for the air. I know they should be build with some good quality in order to store fuel and pass some test but I don't know it those might be suitable to hold air at a pressure of ~2 atm max without danger.

Do you know anything about it? Anyone has been using those for a while or anything else (cheap) comparable?
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Jan 22, 2019, 08:13 PM
JimN8UAY
Jimn8uay's Avatar
I've used this for some time and it works great. I can fill it up and using a regulator it lasts for some time. Every once in a while I see it on sale. https://www.harborfreight.com/5-gall...ank-65594.html

Jim
Jan 22, 2019, 08:46 PM
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Quote:
Originally Posted by Jimn8uay
I've used this for some time and it works great. I can fill it up and using a regulator it lasts for some time. Every once in a while I see it on sale. https://www.harborfreight.com/5-gall...ank-65594.html

Jim
It looks nice, thanks for the link, price it's not bad.
I'm in Europe so it won't do for me, yet it looks like a good solution.
Jan 24, 2019, 08:39 PM
Play that funky music right
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Tanks used for storage of refrigerant or helium for party balloons may be an option. Check with a local automotive shop to see if they have an empty container you can purchase or take out of the metal scrap pile.

Ken
Jan 25, 2019, 02:38 PM
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Quote:
Originally Posted by kenh3497
Tanks used for storage of refrigerant or helium for party balloons may be an option. Check with a local automotive shop to see if they have an empty container you can purchase or take out of the metal scrap pile.

Ken
Thanks Ken, actually I'd rather avoid something metallic, I'm mostly interested in something plastic that I can move easily and does not rust. In case some one else is interested: a terminated fire extinguisher (CO2) from a recycling shop could be an option too.
Jan 26, 2019, 09:25 AM
ARFs Are Me
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eaman

Pressurized plastic sounds like a bomb, waiting to go off.

What precautions are used to keep it from exploding ?
Jan 26, 2019, 12:22 PM
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Quote:
Originally Posted by TomCrump
Pressurized plastic sounds like a bomb, waiting to go off.
That's why i started with a small 1.5l bottle and got a compressor that has a working range around 1.3bar : the power expressed is quite low, the break point of those bottle is around ~11bar, in case it brake I suppose (...) that it would be the connections causing a progressive leakage of pressure, or a delamination of the bottle with no explosion.

There are many tests about these on the web regarding air tanks, home made rockets, cannons, landing gears for RC airplanes, anything that requires a pneumatic energy storage for "hobby" robots and similar. I'll post some link later.

Quote:
Originally Posted by TomCrump
What precautions are used to keep it from exploding ?
For the bottle I can think of two "worst" scenarios: explosion with fragments blasting around, drastic single point failure of the connection (the cap of the bottle) that turns the bottle air tank into a missile in your room.

Again, the first measure is to reduce the potential power: usually air tanks for airbrush compressor are 6l metal enclosure that keep between 5-6bar, just reduce that to max ~1.9bar (which actually translate to 1.3bar with constant air flux, but you usually airbrush between 0.6-0.9bar so that's the pressure you have in the air tank with this setup that does not have a pressure / flux regulator after the air tank, only one in the air compressor).

Than you have weight / material: the plastic bottle is much lighter than metal in case of missile, plastic bottle does not rust, plastic bottle is transparent so it's easier to spot degradation. It's been put to my attention that in case of explosion fragments would be harder to spot in a hospital with an x-ray machine.

For active precautions: http://store.piffa.net/gunpla/comp/final.jpg
You can cover the bottle with plastic tape, that makes the bottle resistant to higher pressure (I've seen over 200psi) and reduces the delamination / fragmentation.

I did no t do that: I just rolled the bottle in a substantial old blanket, then you may want to use some kind of plastic net like that used to hold potatoes ( https://www.google.com/search?q=pota...w=1056&bih=534 ) to keep it firm and prevent fragments to escape. In case it would also alleviate the sound of a drastic failure, which could be the worst part.

This should work also in case of the "missile scenario": main point is that you have a light mass, wrap the blanket so that it has much material by the other side of the cap (where it would impact), put the whole thing in a corner against a wall or under some heavy furniture.

Do your math and see if 1.5l of air at ~0.8bar pressure is adequate for the setup, in case not you may use a 0.5l bottle that is two time more resilient to compression and will generate much less power as it's 1/3 of volume.

Notice: this air compressor is always on, it's not like other setups where you have a pressure switch that turns on the motor at ~3bar and turns off at ~4bar. So the air tank is not there to reduce the motor uptime (heat, noise) but just to reduce the "pulsing effect" of the air compression on the paint stroke.

Regarding the plastic fuel tank as an air tank I've not been able to find anything around about it, that's why I'm asking here before starting on something that is potentially 7 / 14 times more dangerous.
Last edited by eaman; Jan 26, 2019 at 12:30 PM.
Jan 26, 2019, 08:36 PM
Registered User
Thread OP
As for some links, I can share something I've in my bookmarks regarding max pressure and effects of the blast at higher pressure, the idea is that this thing has been done for some time so we have some previous knowledge, but you should always look up for your data yourself and do not trust some random internet guy that promote dangerous staff.

Again: my scenario is ~0.8bar (11 psi, 0.8atm) for 1.5litre of air, I'll leave some links about break point which should be around ~150psi for a 2l bottle.
Please guys do not try any dangerous thing at home, do not put in danger people or pets around you (even annoy them with loud noises).

- http://www.aircommandrockets.com/pro....htm#BurstTest
-
Under Water Burst Tests (1 min 12 sec)

-
Exploding Pop Bottle goes Kaboom ! ! (6 min 6 sec)

-
POWER PRESSURE WASHER ● vs ● PLASTIC POP BOTTLES (4 min 43 sec)

- http://www.sscentral.org/homemade/air_canisters.html
Jan 28, 2019, 12:46 PM
Registered User
Pop2l pop bottles are easy cheap to source.
I've seen videos where 2 are fitted under a small Airbrush compressor.
Seems the bottle caps are the failsafes.. as they let go before the Bottle itself does....at ~200psi
Don't personally see Any issue with using these as air tanks for airbrushing.
Why the long complex postings?
Jan 28, 2019, 02:43 PM
Registered User
Thread OP
Quote:
Originally Posted by Bare
[CUT]Why the long complex postings?
Well one user suggested that this may be dangerous so I went into some details, I feel that he was right to ask about safety issues.

To summarize the long post:
- it's a very cheap setup, 30$ compressor + AB kit with a almost free plastic bottle as air tank
- work pressure is ~12psi and bottle usually can sustain up to 140psi
- No need for a large air buffer as the compressor is always on while you paint, it's only to keep the air flow stable

Plastic bottles are IMHO a better solution than the usual metal air tanks coz they don't rust, they are way lighter, easier for maintenance as they are transparent and don't rust, more than adequate for the pressure (~[8-30]PSI).
Jan 31, 2019, 05:31 PM
Just always blame the wind....
ServiceRep's Avatar

Quiet Air Compressor


This is a very quiet air compressor. I have owned several air compressors from very large to very small. The large ones are noisy and as they get smaller, they even get noisier !
This compressor is quiet. I can use it and still talk on the phone while it is pumping. I would call it a loud hum for a few minutes and then it shuts off.
The best compressor I have ever owned for everything except for powering large air tools.
It has a good regulator and 2 gallons of air. Great for spraying paint. Not to heavy so it is easy to move around.

https://www.lowes.com/pd/Kobalt-QUIE...sor/1000405185
Feb 01, 2019, 12:48 PM
Registered User
Here: genuinely silent .Their TC 20 is best of the affordable breed;
http://www.tcpglobal.com/Airbrushing...r-Compressors/
Feb 04, 2019, 11:30 PM
Registered User
Eamin, Plastic bottles for compressed air is a bad idea. Even at low psi. Its the repeated change that does it. A simple one time test will not show this. Your compressor will make many cycles even when painting for a short time. It will fail at some point, and shards of plastic flying are a bad thing. If you insist on using plastic, change it every use and keep it in a container, contain it, when using.

I understand you want a light air portable tank that takes little space, consider using a tire tube; I have seen then used. When deflated they take very little room.

For those that are looking for a quiet air compressor. Look a the Rolair compressors, excellent products. , I have been using a JC10P for painting etc. and am very pleased. Prices are not bad if you get it from a good tool discount shop. You can run them 24 hours a day.
Last edited by gzkpez; Feb 04, 2019 at 11:40 PM. Reason: grammer
Feb 05, 2019, 08:12 PM
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Thread OP
Quote:
Originally Posted by gzkpez
Eamin, Plastic bottles for compressed air is a bad idea. Even at low psi.
That's interesting, can you link some materials related?
Is this about the fact that the container is elastic (at least in the middle, the cap and bottom are quite rigid as I use epoxy for the junction and it does not break) so multiple changes in its dimension may weaken the material?
I'll look into that. Well I've been using mine for just one month so it may not be enough to cause degradation, it looks fine. Maybe I will pop it and see how much it takes now.

Quote:
Its the repeated change that does it. A simple one time test will not show this. Your compressor will make many cycles even when painting for a short time.
I get what you mean but consider that this particular kind of compressor does not make as many "cycles" as the usual ones with an air tank and a pressure switch, this just stays on all the time.
Quote:
It will fail at some point, and shards of plastic flying are a bad thing. If you insist on using plastic, change it every use and keep it in a container, contain it, when using.
Well if you look at the first post I always planned for this like it may fail in the worst way, I keep the bottle wrapped in a blanket which is hold in a plastic net (or just secure it somehow) to prevent fragments to blast around. It's 1.5 liters of air compressed at ~0.9atm. That's an assumption but I guess that if it's gonna fail for fatigue that would be in a joint or with a delamination that should cause a leakage rather than an explosion.

Yet it's a good advice to change the bottle often, all the work goes in dressing up the cap with a connector, if you drink like 1 bottle of whatever per week you may as well put the new one in place each time. Maybe use a 500 or 750cc bottle, those should be stronger while you have less potential power in case of explosion, after all you don't need that much of a air buffer just to prevent the "breathing effect" of the air compressor.

Quote:
I understand you want a light air portable tank that takes little space, consider using a tire tube; I have seen then used. When deflated they take very little room.
I've seen those and that's what people used some 30 years ago: an old tire tube with a manual pump. I'm not sure how do they behave without a tire on them to keep them from expand, but I guess you can harvest a whole old car wheel for not much, also the pneumatic valves are good to make junctions.
Feb 12, 2019, 08:14 PM
Registered User
The plastic in just about all soda bottles is PET, you can tell by the number 1 in the center of triangle recycle. There are a lot of other bottles, especially non soda, with different plastics out there, that are not as good. I once dropped a PET soda bottle and it shattered when it hit the floor made a mess, that is not suppose to happen must of been made incorrectly or something; they are made fast and cheap. Even purposely built tanks fail, especially when not maintained, rust is a big factor.

If I was to do it I would stick to the 2 litter size. I do not think a smaller one is any less dangerous, as long as you having your bottle contained (like you are planing) it decides to rupture. What you need to do is protect yourself from the parts, by containment; the flying parts can hit your eyes or cut an artery. After that you need to make sure it works, and does not break when you are painting.

As far as using a blanket, I would only worry about the lint getting on your model from it. If you have any contractors 5 gallon pails, I would use one of those to put your 2 litter bottle in. I have way to many of those from painting floors, and driveways etc in my garage. The big box stores around here sell new ones sometimes for 2 or 3 dollars as a promotion sometimes. Or you could use a little trash barrow with a top; if you have one.

The tire I see being used is a set up with a tiny compressor, it is a old tube from some farm equipment or something, smaller then most car tires , I suggested it if you had a tube laying around. They use it all the time for air brushing.


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