Pneumatic tube transport
by Chris Woodford. Last updated: November 25, 2014.
If you enjoying reading the
Sherlock Holmes detective stories, you'll know there's every
chance you'll meet a deadly assassin looming on the next page, ready
to strike at a moment's notice with his poison-tipped blowpipe. These
age-old weapons are classic examples of pneumatic technology: they
use the power of compressed air—blowing hard on one end of a pipe
fires a missile at high speed from the other end. In the late-19th century, around the same time the Sherlock Holmes tales were first published, blowpipe technology
became very popular for sending messages and small objects down much
longer pipes linking remote parts of large buildings. In our modern
age of fiber-optics and the Internet, you might think this rather
quaint "pneumatic transportation" is a thing of the past—but
you'd be wrong. Thousands of hospitals, factories, banks,
department stores, and other places still rely on pneumatic tube
transport to move medicines, cash packets, and other small items with
speed, security, and efficiency. One drive-through McDonald's even
uses a system like this to deliver burgers to its customers! So how exactly do
pneumatic tubes work? Let's take a closer look!
Photo: Need to send cash quickly and securely to another part of your building? You could use a pneumatic transport canister like this. It's made from a tough plastic called polycarbonate, which protects whatever you pack inside. Once the tube is loaded, you screw a cap on the end and place it in the transport tube to be sucked or blown to its destination roughly 5–6 times faster
than a messenger could carry it.
What is pneumatic tube transport?
Pneumatic tube systems (also called PTT, airlift, air transport, Lamson tubes, air tubes, and pneumatic
transit systems) are amazingly simple—and best illustrated by example...
Suppose you run a large department store full of checkouts (cash desks) that are taking money from
customers all day long. To reduce the risk of theft, it's a good idea to
collect that money every so often and remove it to a place that's
more secure before you deposit it in the bank. You could have a
cashier walk around all the checkouts in turn, but that takes time
and it makes the cashier vulnerable to robbery. Also, some checkouts
will take money more often than others, so it's generally better if
the checkout operator dispatches money at regular intervals as it
A common solution many stores employ is to have a pneumatic tube
system linking each checkout with the cashier's department, a strong
room often located on a different floor of the building. Every time
the checkout operator collects more than a certain amount of cash,
they dispatch it securely to the cashier's department using the
Photo: Pneumatic tubes have been used at the US Library of Congress since the late 19th century to send requests between readers and the stores where archive materials are held. The system might seem archaic, but it's tried, tested, and efficient—and still used in parts of the Library to this day. Note the two metaldoors opening up for incoming tubes (left) and outgoing tubes (right, and currently being loaded by the operator). You can also see two spare tubes standing at the bottom. Read more about the system in A Series of Tubes from the Library blog, December 16, 2011. Photo courtesy of US Library of Congress.
How does pneumatic tube transport work?
For simplicity, let's assume we're linking one checkout with the cashier's
department. The checkout has a large metal box called the sending
station with a door that opens onto a tube. Some systems have doors
that lock with keys or open with numeric keypads and PIN numbers;
others are unsecured. The tube (a pipe made of something like PVC plastic or
a strong lightweight metal such as aluminum) runs all the way to the
cashier's department, often only a short distance but sometimes up to 600m
(~2000ft) or so. At the cashier's department, the tube connects to a
more sophisticated box called the receiving station, which may also
have a lockable door. This is sometimes also called the powered
station, because it provides the air power that moves packages back
and forth. It's essentially the same as the sending station, but it
has a compressed air pump attached that can either suck air from the
tube or blow air into it according to which way down the tube
packages need to be sent. Often, the sending and receiving stations
have chimes, ringers, or flashing lights to signal when a package has
just been received.
Most of the time the receiving station will be collecting cash packages from the
checkouts so it will be set to receiving mode (also called vacuum
mode). This means the compressor will be working like a vacuum cleaner so
it sucks air along the tube from the sending station. If someone
wants to send cash from the sending station, they simply load it into
a sturdy cylindrical, plastic canister (only slightly smaller than
the tube and very snugly fitting), place it in the tube in the sending station, and close the
door. When properly loaded, it blocks and seals the tube. Now as the compressor sucks on
the tube, it creates a partial vacuum in front of the canister that
sucks it all the way along until it reaches the receiving station,
where it can be unloaded. Canisters can be sent in the opposite
direction simply by setting the compressor to blow air along the tube
in the opposite direction (behind a canister, pushing it along);
department stores often send small change back to checkouts that way.
Artwork: How a pneumatic transport system works: a tube links the sending and receiving stations. The air compressor pump at the receiving station can suck or blow air. When it sucks, it pulls canisters along the tube toward it; when it blows, it pushes the canisters in the opposite direction.
Just as a vacuum cleaner is limited by the suction power of its
electric motor, so pneumatic
transport tubes are limited in what they can carry, how quickly,
and how far. Typically, canisters are about 5–15cm (2–6 inches) in
diameter and 20–30cm (~8–12 inches) long, made of a toughened plastic
such as polycarbonate, and have rubbery bumpers at the ends to
provide a good air seal and prevent noise as they travel down the
tubes. They unscrew at one end to carry small items weighing up to
about 2kg (~5lbs) or so at speeds of up to 10m (33ft) per second.
That equates to about 36km/h or 22mph—or roughly 5–6 times faster than
a person can walk.
Most pneumatic tube systems are very simple networks linking one receiving station with a
number of sending stations, or vice-versa. However, much more
elaborate, computer-controlled systems are also commonplace, in which
many sending stations link to many receiving stations and packages
can route and transfer in all manner of complex ways; these are the
sorts of systems that hospitals use. A large pneumatic system
might have up to 500 sending and receiving stations, dozens of
transfer units where packages can be routed between senders and
receivers in complex ways, and dozens of compressor/blower units to
provide the pneumatic power.
Advantages and disadvantages
Pneumatic tube systems are a fast, simple, secure, and reliable way of transporting
small objects relatively large distances across a building or (using
underground or overground pipes) between buildings on the same site.
They can move things up, down, or sideways and, because they're
pneumatic, provide a soft, air-cushioned ride for fragile items (many
systems use air-cushioned brakes or bumpers that bring arriving
canisters slowly to a rest at the receiving station). Since they
remove the need for a person to carry things, systems like this save
time and money and tend to pay for themselves quite quickly. They
also offer secure connections between different parts of a building,
reducing opportunities for theft and accidental damage in transit.
If they have a disadvantage, it's that the tubes that link stations ideally need to
be planned into a building's infrastructure when it's first designed
(perfectly possible for something like a new hospital or department
store); it's harder (though far from impossible) to install a complex system
with many sending and receiving terminals into an existing, older building.
Systems like this are widely used in hospitals and department stores, so those are the
places to keep your eyes peeled if you're hoping to spot pneumatic
tubes in action. You're most likely to notice them near checkout desks,
especially when someone sends a bundle of money off to the cashier's department.
Look out for a box (with or without a key lock or numeric keypad)
with a tube coming out of the top and disappearing into the ceiling
up above. You're unlikely to use a system like this directly unless
you work in a bank, store, or hospital, although some pharmacies and
banks do use pneumatic tubes to deliver items securely to
self-service, electronic kiosks.
Photo: Tubes, ancient and modern! This 1942 photo shows the large-scale transport tube system used to connect the main yard office of the Illinois Central Railroad with other offices nearby. Photo by Jack Delano, U.S. Farm Security Administration/Office of War Information, courtesy of Library of Congress, Prints & Photographs Division, FSA/OWI Collection, [LC-USW3-010495-D].
Find out more
On this website
On other websites
These informative articles are worth a look:
Pictures of pneumatic tubes
- Pneumatic tubes: Pictures of tube systems, old and new, that people have shared on Flickr.
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