External Compressor

[andrewganschow]

I'm looking for an external compressor, with low enough pressure (25~30 psi) that won't pop off hoses all the time, but will have sufficient feed to a pneumatics system. I was wondering if anyone here used an external compressor for models, and if so what kind.

[futtigue]

Ive often thought about this same thing. I have a large compressor in my garage, and can run pneumatics through a regulator and nozzle that you would use to inflate a football. Of course, this is inconvenient, as the garage is detached, unheated, and the compressor is very noisy.

Two solutions Ive been considering as I slowly bring together the parts for my own Pneumatic Engine are:

Using a small, quiet desktop compressor sold for hobbyists airbrushes. These are much quieter than typical garage compressors, as they are meant for indoor use. They will not provide the full 90 psi that a shop compressor would, but 40 psi should be fine for lego.

The other solution (and this is the one I am looking into, as my Lego Pneumatic Engine might eventually go in a vehicle) is to use an HPA (high pressure air) canister from a paintball gun. You cannot use a C02 canister, as C02 cools as it expands, and I imagine this would be very damaging to the soft rubber seals in Lego pneumatics (not to mention the moisture). HPA tanks are a bit more expensive (50 or 60$ Canadian or so) and hold air at a very high 2000-3000psi (requiring another regulator) but are light and portable.

Right now I am trying to find a fitting that will connect the special paintball regulator thread (that will not adjust down to below 500psi very accurately) to a regular compressor fitting for a 0-90psi regulator to bring the pressure down safely. From there I would it a handle, and ball inflator nipple.

Hopefully this provides you with some ideas, and maybe someone else has tried one of these.

[JGW3000]

I'm thinking that a fish tank air compressor may do the trick, but these usually are in the 8-10 psig range, maybe higher - I haven't checked. Benefits are quiet and low voltage, plus have easily adaptable hose connections.

[futtigue]

JGW3000,that is an excellent idea with the fish tank compressor. That never crossed my mind.

To revisit my first post, here is someone who used a combination of 2 modified regulators to step down 2500 psi HPA from a paintball tank to 100 psi for an air nailer. If this is possible, reducing pressure to the 40-90psi range that Lego Pneumatics top out at shouldnt be much more difficult.

Edited January 19, 2016 by futtigue

[andrewganschow]

I've looked into airbrushing compressor, never thought of a fish tank compressor. I think the airbrush compressor would work better as it'd provide a better, but the fish tank pump is a very interesting idea.

[dr_spock]

My fish tank air compressor is pretty noisy. I think an airbrush compressor with a pressure control valve would work better.

[Blakbird]

My fish tank air compressor is pretty noisy. I think an airbrush compressor with a pressure control valve would work better.

An airbrush compressor would certainly work better, but aquarium compressors are super cheap. The only question would be whether they provide enough airflow and pressure.

[nerdsforprez]

I'm kinda confused...are u just looking for pressurized air (air tank with compressed air) or also something that not only hold the compressed air but continuously compresses it as well (I.e. Has a motor)? The former would be much smaller and lighter than the latter...

[Twelvebears]

The other solution (and this is the one I am looking into, as my Lego Pneumatic Engine might eventually go in a vehicle) is to use an HPA (high pressure air) canister from a paintball gun. You cannot use a C02 canister, as C02 cools as it expands, and I imagine this would be very damaging to the soft rubber seals in Lego pneumatics (not to mention the moisture).

Any compressed gas cools on expansion - First Law of Thermodynamics. It's just more noticeable on small canisters as the tin cools faster that a large, heavy one. The moisture is just the water in the surrounding air condensing.

As a source of dry, pressurised air, a hobby compressor would be the best option if Jim can stand the noise.

[futtigue]

Any compressed gas cools on expansion - First Law of Thermodynamics. It's just more noticeable on small canisters as the tin cools faster that a large, heavy one.

Sure, but doesn't expanding Co2 create a much lower temperature as it turns from liquid to gas than high pressure air would? I mean, when a paintball gun with a c02 tank is fired enough, you can see 'snow' emerging with the markers. I dont believe this occurs with HPA, but admittedly I am not a paintball expert.

[neonic]

How about a 'compressor' to blow up your tyres? It's a small thing and runs on 12volts.

Or maybe an pump from a car's windowwasher? I know they use them often to feed their, mostly homemade, waterfalls and fountains.

[bonox]

Sure, but doesn't expanding Co2 create a much lower temperature as it turns from liquid to gas than high pressure air would? I mean, when a paintball gun with a c02 tank is fired enough, you can see 'snow' emerging with the markers. I dont believe this occurs with HPA, but admittedly I am not a paintball expert.

Air isn't typically sourced as cryogenic, so a liquefied CO2 source has a greater change of enthalpy due to latent heat effects through the phase change than a single phase expansion of compressed air. Air (or any individual gas) will do the same thing though if you liquefy it and then compare to you CO2 cartridges.

[Chr.Maglekaer]

Revell has these low-pressure compressors for airbrush - http://www.revell.de/en/products/airbrush/compressors.html

[bonox]

The general gas law of pV=nRT has the gas specific marker 'n' (or number of moles related to the atomic mass of the gas) cancel when you compare two different states - two different pressures and volumes to find a change in temperature for example.

edit: as for the 'snow' out of a paintball gun, I think that's a user failure that shouldn't happen if you're using it correctly. If you don't keep the canister upright, you can get liquid siphoning into the chamber rather than the gas, and this rapid expansion behind the projectile gives you the snow. It's hard on the equipment and wasteful of gas

Edited January 19, 2016 by bonox

[futtigue]

The general gas law of pV=nRT has the gas specific marker 'n' (or number of moles related to the atomic mass of the gas) cancel when you compare two different states - two different pressures and volumes to find a change in temperature for example.

Exactly - and we are comparing two different states. There is no need to compare the temperature drop of liquid air as it expands vs. liquid CO2 as it expands, because we are not using liquid air.

It only makes sense to compare the two sources we can use - HPA (a gas) as used for paintball, and CO2 (a liquid which boils off a gas) as used for paintball. I understand that both might see a very similar (and harmful to Lego) temperature drop were they to start out at the same pressure. But, for our practical purposes, they do not.

Which means High Pressure Air from a light, portable paintball (or possibly even SCUBA) tank would be far superior to a CO2 paintball tank (which would be cheaper). This is something that could be used to power vehicles with pneumatic engines, without having to follow it around with a hose!

[andrewganschow]

I don't think canisters would fit the need here. The small revell compressed would be perfect, although I don't have a 220/240 outlet in my little lego corner.

[RohanBeckett]

I bought a small air pump on ebay (was actually advertised as ideal for technic pneumatics)

to be honest, I haven't played with it much, but upon quick test, last year, seemed to work well - which is why it came up in my searches!

I'll dig it up tonight and get details (maybe post a video)

It was fair small... smaller than a D cell battery - possibly around C cell size

RB

[andrewganschow]

Now that sounds like an interesting little compressor there.

[nerdsforprez]

I'm kinda confused...are u just looking for pressurized air (air tank with compressed air) or also something that not only hold the compressed air but continuously compresses it as well (I.e. Has a motor)? The former would be much smaller and lighter than the latter...

I only asked this question because if you are running an LPE or something off of compressed air.... just use a tank. I made a home made tank years ago and just carried it around with me. My LPE only ran for a minute or so..... but for my LPE this worked fine. Easy enough to build... soda bottles and the nipples taken from bicycle tubes......

Another option would be metal air tanks. They can hold much more pressure and if you have a regulator that can release the appropriate pressure to Lego then using a metal air tank you could actually have quite a decent run time

[andrewganschow]

Just looking for a constant compressed. No air tanks needed.

[MSc Shobaki]

My best advise is to buy a Dust-Off spray can for offices. It is used to blow away dust from you office desktop and other things. It also comes with a rigid hose, approx 2,5mm outer diameter. At full pressure I think you get 4 bars of pressure. I have a couple of those at my office where I run my LPE V8 ;) good amount of rpms which makes my collegues drop their jaws everytime I run it.

One spray can here in Sweden cost roughly 10€

Edited January 20, 2016 by MSc Shobaki

[andrewganschow]

I think a three pack here in the US is roughly $4.50

[futtigue]

The small revell compressed would be perfect, although I don't have a 220/240 outlet in my little lego corner.

That link was to an Australian or European site. They dont need to be 220/240v, in fact every single one ive seen here in Canada is 110v. If you're in Canada or the USA it should actually be very hard to find a 220/240v one.

[dr_spock]

An airbrush compressor would certainly work better, but aquarium compressors are super cheap. The only question would be whether they provide enough airflow and pressure.

I did a quick test with a basic air pump from my aquarium.

http://youtu.be/C2rPRa_ZMg4

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http://youtu.be/C2rPRa_ZMg4

It kind of works up to a point. Then it hits a limit. The more expensive aquarium high pressure air pumps for ponds and very large aquariums would probably work better. They are as expensive as airbrush compressors though...

Edited January 21, 2016 by dr_spock

[RohanBeckett]

Ok, so I dug out the pump I bought, and gave it a proper test...

for 6V.. it's actually very powerful! (that's a train/boat weight that it's lifting with ease, in the video!)

Ideally, finding a version that runs on 9V might be more practical...

I found a website that lists the model, and it does say that this one might be ok at 12V, but with a lower current - I haven't tried it yet

Googling 'Mini Pump 9V' yields quite a few results

Anyway.. here's some pics.. and I think the video speaks for itself (esp compared to the fishtank pump! - Sorry Dr Spock! :)

the nozzle/nipple on it IS slightly larger than lego.. but a soft lego hose connects just fine.

Something like this could easily fit inside a decent sized Technic creation.

I can't seem to find any record of how much I paid for this.. I seem to recall around AUD$30?

Edited January 21, 2016 by RohanBeckett