Better 3D printers. Re-use the existing "series of (inter)tubes" to route the specifications. Explosives only cause problems on the end points.

Oh puh-lease! You all know what you're thinking but not saying!
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Portals.


There. I said it.

[quote name='Sirisian' timestamp='1315434147' post='4858835']
ah I was wondering where you were getting your logic. You're thinking of sucking on a straw to generate a vacuum to lift water up against gravity. This property of fluid dynamics doesn't apply to increased fluid pressure. The idea with using a vacuum is to pull the air from the front merely so it doesn't slow down the capsule. The real pressure in the system is pushing from behind which can be an arbitrary amount. Interestingly when you use water in this experiment and decompress it to a vacuum it boils.

The reason banks use push and pull method is because they have only one pump. It's possible to use thin PVC and just use two pumps or use one pump and redirect the pressure to push which is far easier than sucking.

You're simply wrong. It takes the same amount of air displacement to push as it does to pull something through a tube.
[/quote]
Here is a quick thought experiment or you can can go test it in the real world. Take a straw that's 11 meters long which I believe is the limit for sucking water up a normal straw that's invulnerable. Now given your idea it should be impossible to perform the same action by pushing water up the straw. (Hint. It's not because increase pressure isn't limited. It doesn't even take that much pressure really).

Same applies for horizontal tubes. Reading material.

You should read the details of my experiment more carefully.

I'm not talking about creating negative pressure to draw water/air through the straw - I'm actually referring specifically to the opposite. Blowing a specific burst of air out of a 10 foot straw is harder than blowing that same burst of air out of a 1 inch straw, because you have 120 times as much volume to move. (Note that you have to consider moving the entire column of air. Sure you can just push a tiny bit in, and poof, some comes out at the other end; this is not relevant to the package transport theory because you have to move the entire volume of air to completely transport the package from one end of the tube to the other.)

When you breathe through a ten foot straw, one of two things will happen. Either you will fail to move the air out of the straw entirely, and exhaust the oxygen (passing out in the meantime), or you will have to breathe in and out 120 times as much air as if you were breathing through the 1 inch straw (hyperventilating and probably passing out in the meantime). In the first case, you have failed to move the package through the tube; in the second case, you have done vastly more work, and required more constantly-applied force to the package to complete the transport successfully.


That's my logic, nothing to do with drinking through a straw. That would be silly.

I'm not talking about creating negative pressure to draw water/air through the straw - I'm actually referring specifically to the opposite. Blowing a specific burst of air out of a 10 foot straw is harder than blowing that same burst of air out of a 1 inch straw, because you have 120 times as much volume to move. (Note that you have to consider moving the entire column of air. Sure you can just push a tiny bit in, and poof, some comes out at the other end; this is not relevant to the package transport theory because you have to move the entire volume of air to completely transport the package from one end of the tube to the other.)

Why were you bringing up negative pressure then? You don't have to create a vacuum on one end of the tube. You just need to pull the air out as fast as you push air in on the other end. Also yes you're right it's a lot of air since you're basically moving the whole column of air with the capsule, but that's to be expected.

Regarding the breathing system that would be an interesting approach. A check valve pump essentially for generating huge gusts of air.

[quote name='tstrimple' timestamp='1315436285' post='4858843']
[quote name='Sirisian' timestamp='1315434147' post='4858835']
ah I was wondering where you were getting your logic. You're thinking of sucking on a straw to generate a vacuum to lift water up against gravity. This property of fluid dynamics doesn't apply to increased fluid pressure. The idea with using a vacuum is to pull the air from the front merely so it doesn't slow down the capsule. The real pressure in the system is pushing from behind which can be an arbitrary amount. Interestingly when you use water in this experiment and decompress it to a vacuum it boils.

The reason banks use push and pull method is because they have only one pump. It's possible to use thin PVC and just use two pumps or use one pump and redirect the pressure to push which is far easier than sucking.

You're simply wrong. It takes the same amount of air displacement to push as it does to pull something through a tube.
[/quote]
Here is a quick thought experiment or you can can go test it in the real world. Take a straw that's 11 meters long which I believe is the limit for sucking water up a normal straw that's invulnerable. Now given your idea it should be impossible to perform the same action by pushing water up the straw. (Hint. It's not because increase pressure isn't limited. It doesn't even take that much pressure really).

Same applies for horizontal tubes. Reading material.
[/quote]

That's not the same comparison at all. In your magical tube device, there is air behind the object being moved that means that there is no limit to how far a low pressure could move the object.

Your straw in a well would be equivalent to trying to blow an object through a tube that was capped on the end. The positive pressure could move the object some, but you would reach a point where the pressure on the other side of the object was equal to the pressure you were blowing at and the object would stop moving.

Why were you bringing up negative pressure then? You don't have to create a vacuum on one end of the tube. You just need to pull the air out as fast as you push air in on the other end. Also yes you're right it's a lot of air since you're basically moving the whole column of air with the capsule, but that's to be expected.

Regarding the breathing system that would be an interesting approach. A check valve pump essentially for generating huge gusts of air.

Negative pressure does not imply a vacuum. I would like to politely suggest at this point that you need to study up on your physics of non-ideal fluids/gasses before expending too much more effort on this particular theory :-)

I would like to politely suggest at this point that you need to study up on your physics of non-ideal fluids/gasses before expending too much more effort on this particular theory :-)

Your example didn't say anything about the system that wasn't already stated. It's assumed that the column of air must be moving to move the canisters.

Are you arguing that the energy required is too great?

There are two basic ways a pneumatic delivery system can work: positive pressure, and negative pressure.

The negative pressure version requires evacuating air from the receiving end of the line, thus causing a pressure differential within the (sealed) tube. For this to effectively transport objects, you need two requirements. First, the total volume of the tube must not be so great that the package's movement is impeded by friction past a certain point; it is possible to have too little air left in the sending side to push the package hard enough to overcome friction. Second, the evacuation must be done with enough speed and force to overcome static friction and inertia of the package. The more air you must evacuate, the harder this is. Similarly, the larger/heavier the package, the harder this is. Any curvature in the tube whatsoever will also compound the difficulty. My argument against this version is that you cannot evacuate that much air fast enough to create sufficient negative pressure to overcome inertia and friction simultaneously for heavy objects and sustain this over long distances. There's a reason why banks frown on you placing heavy objects in the pneumatic tubes.

The positive pressure variant works by pushing air into the sending end of the line, while allowing air to escape the receiving end. This is analogous to your "pushing water up a long pipe" concept. The problem is, as the package travels, the pressure required to continue pushing it increases, because the volume of air that must be pressurized increases. Remember that simply "blowing air" into the tube will not work, because you need a sealed tube on the sending side. Escaping air will take the path of least resistance and simply vent instead of pushing appreciably on the package. You must account for the constant friction created by whatever mechanism is moving the package, plus the friction needed to maintain the seal, plus the resistance of the entire column of air that must be displaced out of the tube, plus the increasing volume of pressurized air. By the time you move a package even 100 yards, you're talking about massive pressures that would probably rupture the entire system, and at the very least cause dangerous outgassing at the exit point when the package finally arrives. My argument against this version is that you cannot produce enough constant positive pressure to move any appreciable mass over a substantial distance. Eventually, pressure will equalize as the package travels due to expansion inside the sealed tube, or the pressures involved will become too great to be practical.

A hybrid system would extend the maximum reach of a pneumatic delivery mechanism, but not by enough, and not at a sublinear cost for power involved. In other words, it probably wouldn't pay off to hybridize the system by pushing and pulling simultaneously.

If you operated this system in space, where there is an effective vacuum and no friction, you can of course just nudge a package and let it float through space until it arrives; this ignores gravitational effects, of course, and also ignores the incredible difficulty you would have in aiming the package to begin with to make it arrive in the correct location. If you use a guidance or correctional propulsion system, you're no longer operating by pneumatics either, so you're really talking about a totally different concept.


No matter how you slice it, this wouldn't work over long distances. Existing pneumatic systems succeed by limiting the distance and size/mass of objects transported. As soon as you try to remove either barrier, the difficulty of solving the problem scales nonlinearly. You can't just throw N times as much horsepower at it, it's probably closer to N^2.

This is just replacing the system we have now with a near identical automated system that doesn't reuse existing infrastructure. Why not just automate the current postal system? Both projects would probably be feasible in the same amount of time.

Also, there's a good reason packages go through hubs. They would and should do the same thing in an automated system or it would waste a bucketload of energy. It is less expensive to move a lot of things than one thing. The hub system allows you to move many things closer to their destination quickly and repeatedly and only forces you to do the expensive few items to house transaction twice and for a very short period of time.

Also pneumatic tubes would probably turn into a clusterfuck of pressure calculations requiring every computer part in the world to accurately model the amount of mail that gets sent in a single US state every day. Congratulations, you have sent us back to the stone age so we can receive mail.