Ask Engineers ! Pneumatic post transport system
December 2, 2019 8:30 AM   Subscribe

At my place of work we'd REALLY benefit from a means of transporting small objects (wristwatches) pretty directly from A to B then from B to A again, the human route the wristwatches take is long and circuitous, but the route for an object could be pretty direct...

I'd love to build a pneumatic tube transport system, there's a few examples on the web:-

but I'm still left with questions...

How do you go about calculating how tight the radii can be? Should you suck or blow from one end, a point in the middle, do both but from opposite ends etc.

I'd love to backyard engineer this but would love some help!

posted by dance to Home & Garden (13 answers total) 4 users marked this as a favorite
If it's for your work, you could perhaps buy a commercial system? Or at least get a consultation from a company selling them, who might be able to answer your questions (if you're subtle about the fact that you're thinking of building your own). I don't have any specific recommendations, but there are lots of hits on Google for "commercial pneumatic transport system"
posted by richb at 8:40 AM on December 2 [2 favorites]

Another concern I don't see mentioned: Are there any vibration/shock constraints on the watches that need to be met? Some of the systems seem to have a pretty hard stop.
posted by yuwtze at 9:38 AM on December 2 [4 favorites]

There was just an fpp about this: The Cash Railway Website.

I can't find their website, but Lamson - who developed many of these systems in the late 19th century - are still in business.
posted by scruss at 10:04 AM on December 2 [2 favorites]

I'm guessing that the minimum turning radius will depend on the shape of your capsule. A sphere should be able to go around any corner. I have no idea how you'd get a cylinder around a corner without losing too much air pressure to keep it moving, but obviously many professional systems do it.

If you suck, you get a maximum of 15 psi if you can create a perfect vacuum. If you blow, you can get pressure as high as you'd like.

It looks like this is still a big industry for hospitals, so I'd guess that much of the serious engineering knowledge is behind the walls of companies like Lamson, Translogic, Swisslog, etc. So far my searches of Google Scholar aren't giving me much useful information. Pneumatic transport of particulates seems to be much better covered by engineering books.
posted by clawsoon at 10:23 AM on December 2 [1 favorite]

The most I can find so far is a review article by Henry Liu and, if you can find a copy of it, Chapter 7 of his book "Pipeline Engineering" (table of contents). No idea if it covers any more detail than the review article.
posted by clawsoon at 10:30 AM on December 2

I'd look for books, perhaps old ones even, if I was diving into this.

This site also offers an overview with links and patents, the latter might be especially helpful.
posted by RolandOfEld at 12:18 PM on December 2

I've done some pneumatic transfer design for dense phase and dilute phase solids (so, streams of stuff vs containers of stuff) and I have found that there's a LOT of secret sauce wrapped up in how materials interact with piping, and it's not just bend radii: it's material friction, grounding, humidity control. I'd be pretty reluctant to try and homebrew something because I have a sense of how many variables are involved.

The other thing I was surprised when I learned is how incredibly inefficient air transfer is: moving air at the velocities and pressures involved is very energy intensive and means eg that the clearances between the capsule and the conduit need to be snug to avoid side leakage...which then aggravates the risk of jams and the strong need for precisely designed elbows.

That said, commercial "long radius" or "sweep" elbows and conduit may be useful components for you.
posted by hearthpig at 12:26 PM on December 2 [2 favorites]

If points A and B are on the same floor, I’d look into using an O scale model railroad, like Mr. Rogers had.
posted by bigbigdog at 12:55 PM on December 2 [4 favorites]

Does it need to be pneumatic? How big a distance are you talking? Could you do something where your small containers are hooked onto ropes that are moved on pulleys?
posted by beandip at 1:23 PM on December 2 [1 favorite]

I assume you've already looked at all the options from the recent Cash Railway FPP.
posted by clawsoon at 2:46 PM on December 2 [2 favorites]

At the last few annual congresses of the Chaos Computer Club in Germany, there has been a temporary pneumatic tube system around the venue, built from standard flexible drainage pipe and vacuum cleaners.

They have been doing this for several years, so have had time to refine things and make it cheap and easy to deploy. They publish capsule specifications so that anyone can build their own capsules to be compatible with the system. Might be a great reference & source of advice if you're thinking of building your own DIY system.

Website for the project and wiki page from last year's event.
posted by automatronic at 1:40 PM on December 3 [6 favorites]

@automatronic - that website looks like it will be a GOLD MINE thank you so much!
posted by dance at 6:31 AM on December 5

Thanks all. @clawsoon, look at the effect these German lads are getting with just suction. It's amazing.
posted by dance at 3:45 AM on December 6 [1 favorite]

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