Are Closed-Loop Systems Possible?

[GeorgeCrecy]

Hello one and all,

For those that have more experience with pneumatic systems, I was wondering if a self-sustainable, closed-loop system is feasible with LEGO pneumatics? 

I have been toying with the following idea in my mind: Air tanks lend air to an engine and to a power generator, leftover air from the engine going to a turbine, and from that to two compressors. Power from the pneumatic power generator goes to the lego-built compressors which resupply air to the air tanks. 

Would such a system work? Or am I looking at a pipe dream (pun intended)? 

[higgins91]

If you put this to perfection you will be the inventor of the perpetual movement! well done :)

[Mechbuilds]

It will work for a little but then stop due to losing power due to heat made by friction, eventually stopping. 
Or it will simply just not move. 

[TeamThrifty]

Perpetual motion! Check out the laws of thermodynamics... you're violating them!!! 

[Zerobricks]

Sounds like you're trying to blow on your own sail...

[CrankyCraig]

A pipe dream I'm afraid. It will work for as long as it takes for the air pressure in the system to equalise after opening the valves on the tanks.

Props for the cheeky shot at physics though. It's always worth it on the off chance you catch it sleeping.

[doug72]

NO

[letsbuild]

I think you're all reading this wrong. 

My understanding is instead of bringing new air from outside into the system, using it, then ejecting it back outside, he wants to fill a loop with air, routing the "exhaust" from the cylinder straight to the "intake" of the compressor.

@GeorgeCrecy am I right?

EDIT: I read that wrong. He's definitely talking about a perpetual motion machine.

In that case, you could still have a "closed-loop" pneumatic system, you just wouldn't be able to power your compressor from it. You'd have to bring power in from elsewhere.

Edited May 20, 2020 by letsbuild

[doug72]

9 hours ago, letsbuild said:

EDIT: I read that wrong. He's definitely talking about a perpetual motion machine.

In that case, you could still have a "closed-loop" pneumatic system, you just wouldn't be able to power your compressor from it. You'd have to bring power in from elsewhere.

There was a discussion topic on this way back in Nov 2017. I have a book which has  chapter on this subject with 50+ examples of supposed Perpetual Motion - NONE of which would worked.
See this topic: unfortunatley the video showing it apparently working no longer available. but it must have had either a hidden motor or HOG pulling a string off scene.

I made a Mock PM GBC module, which would have used a hidden motor behind the white back scene had I finished it.
See this post

 

Edited May 21, 2020 by Doug72

[letsbuild]

29 minutes ago, Doug72 said:

There was a discussion topic on this way back in Nov 2017. I have a book which has  chapter on this subject with 50+ examples of supposed Perpetual Motion - NONE of which would worked.
See this topic: unfortunatley the video showing it apparently working no longer available. but it mast have had either a hidden motor or HOG pulling a string off scene.

I made a Mock PM GBC module, which would have used a hidden motor behind the white back scene had I finished it.
See this post

 

The system I'm thinking of is one where the air is entirely contained within the system but the compressor is powered by an external battery. Not perpetual motion. I know that is impossible

[Lipko]

39 minutes ago, letsbuild said:

The system I'm thinking of is one where the air is entirely contained within the system but the compressor is powered by an external battery. Not perpetual motion. I know that is impossible

Put the whole system in a big closed tank and voliá, closed system.  seriously though, it should be possible but I don't how much practical usage would it have. Maybe on a submarine or is space or similar. Air is "free", if you have to put energy in the system anyway, you could just pump air and use it as the energy source.

Hydraulics is quite close to a closed system. Any "vented" oil goes back into the oil tank. In case of pneumatics, you just vent to the atmosphere, no need to lead the "zero energy" air back anywhere.

Edited May 21, 2020 by Lipko

[Didumos69]

A closed loop system is a system with a feedback mechanism that regulates the primary system. That should be doable with LEGOs. Self-sustainable is not possible.

I think this classifies as a closed loop system:

 

Edited May 21, 2020 by Didumos69

[dr_spock]

I think it is doable in virtual reality.  There is one way to find out.  IRL, grab some parts and build it.

 

 

 

 

[JGW3000]

Closed-loop fluid systems are very common - anyone with an air conditioner or refrigerator has one. As long as an external source of energy is supplied and the system is kept free from leaks, a closed loop system will operate indefinitely, until parts or seals wear out, which usually happens on the hottest day of the year 

[pleegwat]

Lego compressor pumps take in outside air, and air escapes through the three-way valves if they are not in the center position. I think I read once (during my dark age) of someone who ran fluid in lego pneumatics, and that was difficult because of those two points of outside interaction. He basically had to submerse the compressor pump's intake valve in a liquid bath, and make sure all three-way switches were in or above that bath as well.

You could set up a closed loop system if you don't use compressors or valves, but then all you'd be able to do is synchronise the movement of two or more cylinders. That probably does have applications.

[GeorgeCrecy]

Hey there everyone,

Wow! I need to check my settings, I got no notifications about this thread getting replies.

In any case, I realize this is quite theoretical, and that the lego pneumatics introduces many opportunities for leakage between connections, but here is what I am mainly trying to accomplish in a better way than I explained originally:
I am attempting to recreate through lego multiple pneumatic engines powering different things, and these pneumatics being supplied sequentially from multiple custom air tanks made from plastic bottles for longer run times. There would be four things needing air: 1) main reciprocating engines under some load, 2) a "turbine" also under some load, 3) electric generating engines, and 4) the return to the bottles. I suppose it isn't entirely necessary to reuse the air for the compressors when I could instead reroute any leftover air for another purpose I have in mind. But, as others were mentioning there might not be enough leftover and/or other problems might also arise. So perhaps it would be better to use the term closed-loop in regards to the electric generators helping to power both the compressors (regardless of where the incoming air comes from) and lights for the overall build. And regarding the turbine, especially for like a 10-12 stud wide cylinder for it to be the scale I am intending, it might be better to just hide a smaller and easier to build turbine inside.

Anyway, thanks to everyone for your thoughts on the idea so far, I look forward to any more feedback, and if I can I will see about testing my model IRL. We shall see!
P.S. For any interested in what in the world I'm trying to do with this, I might direct you to a previous post of mine where I have some in-progress pics of the engines themselves (in LDraw): 
https://www.eurobricks.com/forum/index.php?/forums/topic/156278-need-help-replicating-historic-engine-system/&tab=comments#comment-3171756 

Edited June 16, 2020 by GeorgeCrecy

[aeh5040]

Closed-loop pneumatic systems definitely can be and have been done in LEGO.  Several people were experimenting with them in the early 2000s IIRC.  I think there were discussions in the old LUGNET Forum - I don't know how easy they would be to find.  The basic idea was to use multiple switches mechanically linked so that the hidden fourth port is never connected to anything...

Edited June 16, 2020 by aeh5040

[Erik Leppen]

All I can think about regarding this topic is the alternative model of 8868 (one of the most innovative models, like, ever), but I don't know if that's what the topic starter meant...

[DrJB]

I think all of us have different definitions of 'Closed-Loop' ...

1. Perpetual machine, compressed air keeps on moving downstream, and actuates many picstons, pumps, ... etc - Strictly speaking: NOT Possible, unless #2.

2. Same as above, with a constant supply of air - Very possible/doable. In fact, all you have are transducers/switches/pistons all connected in series, with a constant fluid input at some end.

3. Regulated/Controlled Systems. Where a variable is measured/sensed and then the system 'adapts' its dynamics to perform some function. The AC example above is valid. The AC measures the temperature, and based on such temperature it decides to turn cooling on/off. Strictly speaking this is On/Off control ... not continuous. The best example here is the self-balancing robot that came with Mindstorms EV3.

[aeh5040]

What I was talking about (and I think what the OP may be talking about) is a 4th possibility: a pneumatic system in which there is no input or output of air (so the air could in principle be replaced by some other fluid).  This has been investigated and done.

[DrJB]

Thank you, good point. Care to provide more details? I have a 'hard time' understanding/accepting that a system keeps on moving forever as the first law of thermodynamics needs to hold. Or maybe, my understanding is off, regarding this specific topic.

[Lipko]

On ‎6‎/‎18‎/‎2020 at 5:22 PM, aeh5040 said:

What I was talking about (and I think what the OP may be talking about) is a 4th possibility: a pneumatic system in which there is no input or output of air (so the air could in principle be replaced by some other fluid).  This has been investigated and done.

It is called hydraulic system...

[aeh5040]

4 minutes ago, Lipko said:

It is called hydraulic system...

Hydraulic means using an incompressible fluid (i.e. a liquid), which is probably not a good idea with the LEGO pneumatic parts..  Pneumatic means using a gas (e.g. air).  However, yes, a closed loop is what you would need for a hydraulic system.

[Lipko]

As I wrote earlier, I see no point in closed loop for air for everyday use, since you have it everywhere freely and it's not that hard to condition it. Venting things against a pressure (something that would build up in a finite volume closed loop) would just decrease the power you can get with using air (less force in a cylinder since you have a counter acting pressure).

[aeh5040]

On 6/22/2020 at 7:13 PM, Lipko said:

As I wrote earlier, I see no point in closed loop for air for everyday use, since you have it everywhere freely and it's not that hard to condition it. Venting things against a pressure (something that would build up in a finite volume closed loop) would just decrease the power you can get with using air (less force in a cylinder since you have a counter acting pressure).

No particular disagreement from me on that.  But, some people want to tackle it because it's there!

Edited June 23, 2020 by aeh5040