Pneumatic mail: principle of operation

Perhaps the strangest cargo ever sent by air mail is living people. A report from 1869 on the movement of a 15-year-old in a pipe near London, in a London Pneumatic Despatch Company trailer: “The journey from one end station to another took nine minutes. The journey was exciting every time, the air was fresh and cool even on the hottest summer days. From Holborn Circus, the pipe was diving down a steep slope to Farrington Street, and the speed reached 60 miles per hour. In the dark, I felt like flying down a mountain, feet forward. The accelerated trailer skipped up the hill to Newgate Street. For the first time, it seemed strange and even frightening to this flight underground, so close to the surface that the sound of hooves and the roar of wagons were heard. ”

Piston Arrival

However, the first trips by pneumatic transport began a quarter of a century earlier. 1844, a suburb of Dublin, 200 passengers occupy seats in the world's first train "atmospheric railway" in the town of Dalki. The cars in it are completely ordinary, there are seven of them, but there is no locomotive in the train! Five minutes before departure, a bell rings and the steam engine starts to pump air from a pipe 40 cm in diameter laid between the rails at a point of arrival almost 3 km away. There is a piston in the pipe that is hooked onto the first carriage truck. The driver removes the train from the brake, and the cars smoothly gain speed. The train noiselessly, without the usual locomotive smoke and soot rises uphill and arrives at the final station in a few minutes, having traveled at a maximum speed of 64 km / h.

This trip made a lasting impression on contemporaries. Returning the train, without frills, rolled down the hill, and third-class passengers helped him to get under way - they got out and pushed.

Since the 30s of the XIX century, pneumatic transport has developed rapidly. It is interesting that progress in this area went along the path of size reduction - from passenger cars of the 19th century to compact capsules of our time.

Clearly, creating traction using a pipe of small diameter is easier than building a tunnel the size of a railway wagon. But, so that the piston connected to the compound could move, a slot had to be made in the pipe along the entire length. And how to close this slot hermetically? We settled on a variant with a leather flap valve: a passing piston opened it, and a roller mounted on a wagon trolley closed and sealed it.

The valve models worked perfectly, but in real life it turned out as always: in the heat, the skin dried and cracked, it froze in the cold and warped. At night, crowds of rats ate deliciously fat-soaked skin, and the first morning piston brought a generous crop of carcasses to the station, mixed with condensate accumulated overnight.

In order for the valve to work satisfactorily, after each train, a worker had to be let in, who would lubricate the valve and press it against the pipe. A beautiful idea turned into a headache, and after ten years of operation, the first pneumatic railway was closed.

The drawing dates from 1870 and depicts a passenger cabin of a pneumatic carriage at the Broadway station of the New York subway.

Sarcophagus for senators

More successful application of pneumatic traction turned out to be mail transportation, but they did not immediately abandon the idea of ​​carts on wheels. In the early 1860s, the London Pneumatic Despatch Company connected several London post offices with a miniature railway tunnel about 120 cm high. Cargo capsules ran about 60 cm high and 2 m long along the rails, equipped with a rubber seal for sealing. Each capsule could carry up to 3 tons of cargo per flight at a speed of up to 60 km / h.

People who wanted to ride through the tunnels also felt quite comfortable, especially if they put a mattress in the capsule. The most furious optimists believed that the day was not far off when sirs and peers after a working day in parliament could not drag home on London traffic jams, but quickly rush to their native land in underground tunnels.

The vacuum created a "pneumatic wheel" - a design of rotating metal disks with a diameter of 6 m, which, like a centrifuge, ejected air from the tunnel. Alas, it was difficult to seal even a small tunnel, so it was not always possible to create the required pressure drop. The wheel was modified, but even when its power was six times higher than the original, the system worked unstably and the capsules constantly got stuck in the tunnels. In 1875, the company was liquidated.

Postal artillery

By this time, the idea of ​​a “tube-capsule” survived yet another metamorphosis and finally found successful application. Smoothly curved metal pipes of small diameter, the capsules that fit into them, moving like shells along the trunk, huge cobwebs of diverging star-shaped mail lines. One after another, European capitals acquired classic pneumatic mail. At the peak, the size of the networks reached impressive proportions: in Paris up to 467 km, in Berlin - up to 440. Tens of millions of messages were sent annually.

Each network had its own pipe and capsule size. In Paris, a fragile young lady could handle the forwarding of messages, and in New York, far from white collars worked by mail. Severe New York capsules with a diameter of 20 cm and a length of 61 cm were made of steel, so their weight reached 9.5 kg. They looked like shells, and the workers who loaded them were called rocket launchers. To prevent the capsules from getting stuck, from time to time a perforated container with lubricant was let through the pipes - therefore the capsules were constantly dirty. Sometimes the “rocketeers” were given working aprons, but more often they simply offered to work in dirty clothes, tea was not a bar!

A label with an address was attached to each capsule from the outside, so they did not have to be opened between the stations. And capsule jamming sensors were “control fans” at each receiving bell. As the capsule moves, it pushes air in front of it, and the fan rotates. If the fan stops, you must act. The operator called the central station, and, determining where the capsule came from, the mechanic increased the pressure at the departure point and decreased at the arrival point. In 99% of cases, this helped. Well, if you were unlucky, you had to dig the streets.

Pneumatic mail worked in any weather and was not dependent on road conditions. But its maintenance was expensive, in addition, the throughput of capsular pneumatic transport is very limited. The capsule of New York mail, not the smallest among the existing ones, included a maximum of 2.5 kg of mail, and no more than four capsules were sent per minute. And to cross this threshold was impossible. Therefore, with the proliferation of telephones and automobiles, urban pneumatic mail systems closed one after another.

Swiss company Swisslog develops medical equipment for leading European clinics. Among its products there are also containers for pneumatic mail - reliable, airtight, with an antibacterial coating. Each container is equipped with an RFID tag, due to which the computer centrally monitors the position of all containers in the system.

Money down the drain

Pneumatic post did not give up and continued the struggle for survival. She cringed again to settle in large office buildings, and held out there for quite some time. Even turned into a symbol of bureaucracy. But electronic document management knocked her out of these positions. Then she occupied narrow niches - large enterprises where it is important to quickly send small items.

Of course, the most relevant is cash. In large stores, cashiers quickly accumulate significant amounts. So it is not far from the robberies. And using secure pneumatic mail, it’s easy to send the proceeds at least every three minutes to a remote safe room. In banks, on the contrary, operationists receive exactly as much cash at the workplace as they need at the moment.

In the container, you can transport both documents and laboratory glassware, small devices, and even liquids. There are also special cleaning capsules for piping care.

I found less obvious application of pneumatic mail in large clinics: it is the quick sending of tissue samples to the laboratory for medical tests. For this task, it is important that the capsule smoothly slows down, and does not arrive at the destination station as an artillery shell. In modern systems, air is supplied to the incoming capsule, and it gradually slows down.

The third application is sampling in production. There are systems that allow, for example, to scoop up a sample of molten metal and automatically send it for testing.

The principle of operation of pneumatic mail for 150 years has not changed. But materials and management have reached a new level. For example, now each capsule can be tracked individually and automatically sent to any point on the network, connecting up to several hundred users. And if the capsule is stuck, electronics will determine its location.

Product pipeline

Each type of transport has its pros, cons, and the balance is constantly changing. Cars provide freedom of maneuver, but burn oil, with 70% of the fuel spent on moving the car itself, and only 30% on moving cargo. Many cars are traffic jams, accidents, endless construction and repair of roads. Fuel is not getting cheaper either. The search for alternatives does not stop, and capsular pipelines are one of them.

The idea seems eccentric, only until you think about how much a city dweller receives every day through pipes of liquids and gases. For example, 10 tons of water per month per person is a very economical calculation. It would be real madness to try to bring, and after use, also take away all this mass with cars. Sewerage, gas pipelines and oil pipelines, the movement of bulk materials in production - pipelines are everywhere, there are so many of them that they simply merge with the landscape. Streams move day and night, invisible, silent, environmentally friendly. And to move large objects through the pipe, it is enough to put them in transport capsules.

Noel Hodson, Foodtubes Project Coordinator, explains that it’s best to introduce pipelines to big cities. A pneumatic delivery network in the London Croydon area with a population of 52, 000 people and a hundred supermarkets will cost $ 300 million and will fully pay off in five years. And most importantly, save the area from the arrival of 700 trucks every day. The Foodtubes team is confident that when the first network is built, other areas will want the same, and gradually the networks will merge into the citywide web.

A group of researchers from Imperial College London suggests using the roller coaster experience for capsule piping. At these attractions, the wheels of the trolleys are fixed in the rail, which means that the pipe does not direct the capsule and the load on the pipe walls decreases sharply. Therefore, instead of steel, you can use simpler and cheaper plastic pipes.

However, even if we see product pipelines and pipelines in real life, most likely they will not be completely pneumatic. One of the main limitations of pre-pneumatic pipelines is a small capacity, because at the same time only one composition can be in the pipe. Accordingly, the longer the pipe, the less its useful load. A possible solution is to accelerate the capsules not with air, but with electric linear motors, simple, reliable and cheap. But that is another story.

The article “Case is a pipe” was published in the journal Popular Mechanics (No. 9, September 2014).

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