
Basics of Pneumatic Logic - Koshkin
https://www.hydraulicspneumatics.com/technologies/pneumatic-valves/article/21122363/basics-of-pneumatic-logic
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emersonrsantos
I love pneumatic logic! I’ve gone to sleep many nights thinking about
pneumatic logic gates, and they are still used today on pneumatic equipment
powered by wind, like a lot of pipe organs in Europe made in the 1800’s where
there was no electricity to turn on and off the pipes.

Here’s an example of such apparatus:
[https://www.woodofhuddersfield.com/uploads/1/1/2/3/11238427/...](https://www.woodofhuddersfield.com/uploads/1/1/2/3/11238427/tubes_orig.jpg)

~~~
Animats
Yes, some pipe organs had enormous switching systems. They didn't do all that
much; they just switched the keyboard to pipe rank connections. Physically,
they were huge, like multiple upright pianos. Some needed compressed air for
power; others were entirely electrical.

They had no direct function in producing sound. All this was separate from the
actuators for the pipes.

~~~
emersonrsantos
Exactly, what produced the sound was pipes (and is, in a non-electrical or
electronic organ) using the same air that feed the pipes by the bellows.

It replaced mechanical track action, keyboard coupling, register switching and
even had memory to ‘remember’ a register presets or register sets.

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beambot
If you like that, you'll get a kick out of fluidic logic -- used in old-school
ICBMs, oscillators for spraying wiper fluid, etc

[https://hackaday.io/project/45555/gallery#5233f682e2114006e2...](https://hackaday.io/project/45555/gallery#5233f682e2114006e27d5fd5b5e37760)

[https://en.wikipedia.org/wiki/Fluidics](https://en.wikipedia.org/wiki/Fluidics)

Also worth checking out Bubble Logic (PDF warning: it's an MIT PhD thesis):

[http://cba.mit.edu/docs/theses/08.09.Prakash.pdf](http://cba.mit.edu/docs/theses/08.09.Prakash.pdf)

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fringleot
Still handy in ATEX rated zones

EDIT: a little more context.. ATEX rated zones are where there may be or
always is an explosive atmosphere, this makes computer controlled systems an
interesting challenge.

IMHO control systems are all distributed systems and from a creator centric
perspective there is something exceptionally satisfying when part of the
distributed logic and state management is in pneumatic valves.

IANAL or expert but it is also an ingenious way to get around IEC 61508
complexity. When I worked on control systems priority one for safety concerns
was making logic physical (not software at all) as it is very very hard to
prove software running on an OS is in any way safe - while engineering
diagrams with know failure modes etc was deemed preferable (by our team at
least).

again: not a lawyer or expert :)

~~~
arethuza
Many year ago, I worked on a project providing training simulations for the
Reactor Shutdown Safety Sequencing Equipment (RSSE) of a UK AGR power station
- the project manager had been involved in the construction of the plant and
explained that the equipment involved actually used mechanical sequencing
essentially based on clockwork as it was designed using technology that was
_really_ trusted when the AGR plants were first designed in the 1960s - which
basically meant 1940s level technology.

Edit: Pretty sure I have the words in RSSSE correct though perhaps not in the
right order.

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yummypaint
Heres another page on the same site with more extensive info and examples:
[https://www.hydraulicspneumatics.com/technologies/other-
tech...](https://www.hydraulicspneumatics.com/technologies/other-
technologies/article/21883874/book-2-chapter-2-air-logic-circuits)

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jessaustin
If you've ever been to the dentist, you've probably been pretty close to
pneumatic logic. Every delivery unit I've seen has used it. (Power a handpiece
only if it's not in its holster, spray water only when the water switch is on
and the handpiece is turning, etc.) Fixing them is a pain. You have to have
just the right rubber sheets, gaskets, o-rings, etc. Also they're just a block
of metal with a bunch of hoses attached. It's impossible figure out what an
individual valve does just by looking at it.

~~~
VBprogrammer
I believe very similar control circuitry is used in aircraft landing gear
hydraulics. For example to open the landing gear doors before extending the
legs.

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quickthrowman
There are still pneumatic controls operating HVAC equipment all over the
place. A lot of it is being replaced with electronic temperature controls as
the service life of the existing HVAC equipment comes to an end and it gets
replaced. Facilities are now looking to interface HVAC temperature controls in
with wider building automation systems.

The only context I see pneumatic controls in is a system to be demolished and
replaced, so it’s neat to see how they work and how they’re functionally
equivalent to electronic logic gates.

~~~
userbinator
That's sad to hear, because the original controls would probably outlast the
new electronic stuff with only a bit of regular maintenance.

~~~
meditative
There's no remote monitoring, they're more complex and expensive. You need
either multiple compressors, or run long stretches of hose/pipe.

They're super cool and rewarding to work with, everything feels like steam
punk, but there's no real practical reason to keep them there. The electronic
stuff is _very_ reliable when installed correctly and quality parts are used,
much like the pneumatic systems.

The only place that _might_ make sense to leave them in a little longer is
inside a hazardous environment, which requires detailed certification for
installed electrical equipment.

~~~
ganzuul
Since a bad solar flare could mess up our electronic stuff we should at least
keep the equipment we need to rebuild society not sensitive to EMP.

~~~
danielheath
Still easier to shield existing digital gear for EMP. Compared to the cost
when one inevitably does hit the shielding is dirt cheap.

~~~
ganzuul
You should test that shielding though, and AFAIK the dangerous voltage enters
equipment through cables. Unless everything is fiber optics you would need
some chonky optocouplers on all signal paths.

Pneumatic air is usually supplied with plastic tube and hose. There are no
unexpected electrical circuits coupling to unrelated equipment.

~~~
meditative
it will no doubt damage a lot of equipment, it's still cheaper to replace
everything than to have incompatible spare pneumatic gear laying around.

~~~
ganzuul
I think the problem is one of bootstrapping. With PLCs controlling even sewage
pumps society will have a lot of more important things to do before we come
around to fixing elevators, automatic doors, or even chip fabs. Then there are
herds of forgotten VAXen and AS400s that have been chugging along for decades
running who knows what mission critical code, all gone without as much as
specs remaining.

The less basic infrastructure which is wiped out the faster we can rebuild.
Right now it looks like we will be falling back to whatever cam-actuated
automatic lathes which have not been sold below scrap value that are left. And
I hear those things are a bitch to set up.

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spiralganglion
For anyone unfamiliar with those ANSI valve symbols, you'll find a charming
explanation of them here:
[https://www.lunchboxsessions.com/materials/hydraulic-
schemat...](https://www.lunchboxsessions.com/materials/hydraulic-schematic-
symbols/introduction-to-valve-symbol-reading-lesson)

(Disclosure: I'm on the team that built this site)

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twirlip
Oh, I've only read about pneumatic logic in Ted Chiang's "Exhalation" and Neal
Stephenson's _Cryptonomicon_. How neat to read about actual gates and their
functioning.

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rypskar
This brings back memories. The first "programming" I was exposed to at school
was using pneumatic. I remember one task was to construct a system to act like
the doors on a buss, where one button is used to both open and close the
doors. Working with real components make the logic so much more intuitive.

~~~
ganzuul
Lots of maintenance guys are also exposed to boolean logic through pneumatics.
Expectations are not super high but surely some students discover a fondness
for logic this way.

Edit: Reminds me, Festo makes some really unexpected and creative stuff but
ostensibly they produce pneumatics. I would really like to know what kind of
culture is behind this creative bent of theirs and if it is related to logic.

~~~
rypskar
It is incredible what some used to do, I once used a day or two trying to
document an old logical system that was using 20-30 relays and contactors by
tracing the wires. Did end with giving up and had it rewritten in PLS-code.
The old system was created a long time before I started working there by
someone who where good at that kind of work and never learned to code in PLS.

I don't know how it is done now, but at least 20 years ago more advanced
systems where expensive and creating something using logical gates was what we
where used to, so used that for simple systems. In some ways creating
something using logical gates and get it to work is like doing something
simple with command line tools instead of writing lots of code to do it

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Koshkin
Apparently the idea of "jet logic" as a useful substitute for electronics in
some situations (hence dubbed "pneumonics"), gained some popularity in Russia
back in the '60s. Here is a moment in a fascinating educational video where
they explain the workings of a jet NOR/OR gate:

[https://youtu.be/gzGRLdB0BpE?list=PLgqu8dCNRlmX_d0Oz3T6gRTyw...](https://youtu.be/gzGRLdB0BpE?list=PLgqu8dCNRlmX_d0Oz3T6gRTywGgKumJGl&t=697)

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thro1
You may enjoy: Escape Pod 194 - Exhalation

[https://escapepod.org/2009/04/10/ep194-exhalation/](https://escapepod.org/2009/04/10/ep194-exhalation/)

[https://traffic.libsyn.com/escapepod/EP194_Exhalation.mp3](https://traffic.libsyn.com/escapepod/EP194_Exhalation.mp3)

16:22 - debugging self own pneumatic brain

How this kind of logic works with reverse airflow? (Would it be like time
going back when Inhalation?)

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amelius
Downsides:

Mechanical wear, leaks, difficulty to put a pressure probe at various points
in the circuit, slow speed, size, complicated 3d geometry, need for compressed
air, audible noise, ...

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emmelaich
The original 'series of tubes'!

I've commented on HN before that Ted Stevens attended engineering school in
the heyday of pneumatic machines.

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sova
This reminds me of the recent moving visual on twitter of "fluid logic gates"
where streams of water represent incoming electricity.
[https://twitter.com/page_eco/status/1188749430020698112](https://twitter.com/page_eco/status/1188749430020698112)

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bencollier49
I suppose this article might be useful to Dwarf Fortress players; I'm not sure
if it's minecart logic or fluid logic which is en vogue right now.

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sircastor
I was just looking up "pnuematic computer" a couple of days ago. There was an
ad from Target telling me they had pnuematic computers.

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kwhitefoot
It's a pity they didn't explain how the gates actually work.

