Air makes a blast

The ability to release an air pulse very quickly enables the manufacture of many novel products, the most important of which could save many lives. Tom Shelley reports

The ability to release compressed air within a millisecond has allowed the development of compressed air 'guns' with a multitude of uses.
Objects, including long lengths of cordage, can be launched up to 100m, without having to resort to explosives.

And shocks can be delivered to free up powder blockages, and single blows or pulses of air delivered to simulate a variety of physical processes. But best of all, the valves look to be a better way of powering the multiple air bags expected to be required on the next generation of cars to be sold in the US and elsewhere.
Pneumatic air cannons which, deliver sudden pulses of air are quite well known. It is even possible for readers to make them themselves, although we at Eureka will take no responsibility for what readers may do to themselves if they try.
One design available on the Internet requires only a ball valve, some lengths of pipe and a rubber disk. A family of products developed in Russia, however, uses a patented valve which responds unusually quickly, and the company has devised products which are completely self contained, and which resemble and can be used and aimed much in the same way as a 'bazooka' rocket launcher.
Russians seem to like developments which go with a 'bang' and perhaps for this reason, lead the world in explosive forming and bonding techniques.
This particular family of products is made by Ista, a company spun out of a research department at what is now the St Petersburg State Technical University. The names on the original patent are Dr Sergey Isakov, now Ista's chief executive officer, and Dr Sergey Yurkin, now the technical director. The principle behind most air cannons is to store compressed air or gas, and let it go suddenly, by releasing pressure holding some kind of valve or diaphragm in place.
The valve in the Ista design is conical, and release of gas pressure inside the cone causes it to be pushed backwards away from its seat, and allows gas to rush past the outside of the cone in such a way as to minimally restrict passage. Most of the other designs around, with pistons and diaphragms, which step backwards require the escaping gas to make some kind of a 'U' turn. This inevitably reduces final gas velocity, which to be useful, needs to be as high as possible.

Ista products have the ability to throw a cartridge releasing up to 100m of line. One of these devices was recently seen on Russian television when it was used to help rescue a man stuck on an ice floe. The method used in the West is to use a rocket attached to a folded line. The rocket can only be used once, which can be unfortunate for the people being rescued if it happens to miss and there is no replacement, and the line takes a very long time to re-fold round all the pins in its holder.
The most common use of the products in Russia is to break down bridges and funnels formed in powders, particularly bakery flour, in hoppers and bins. Delivering a sudden pulse of air to the powder is less damaging to a construction than fixing mechanical vibrators fixed to the outside, and far less damaging as well as more effective than hitting the outside with a sledgehammer.

The company has so far supplied a substantial number of units: 85% to bakeries, 10% for rescue work, and 5% to laboratories. Shock waves delivered by air cannons are much less hazardous for student researchers to work with than explosives.
The really exciting possible application, however, according to Dr Yurkin, is to use the valve in the next generation of automotive air bags.
Airbags are particularly favoured in the USA where it has been found difficult to persuade drivers and passengers to always wear seat belts. Research has shown that because crashes do not always happen head on, front air bags are not sufficient to protect occupants. In particular, when the increasingly popular sport utility vehicles roll over, which they are liable to do because of their high centre of gravity, it is essential to have side air bags if occupants are to avoid death or serious injury.
New designs being studied by Mercedes Benz, among others, involve the use of up to eight air bags in a single vehicle. Present technology requires the use of pyrotechnic squibs. Use of compressed gases could be at the same time cheaper, less hazardous, and more flexible. One gas vessel could power several adjacent bags, and valves could open according to which bags were needed instead of firing all of them.
To those who would say that gas valves would be likely to have an unacceptable amount of leakage over time, one has only to point to gas filled fire extinguishers. Fire extinguisher valves generally do not leak, but their gas fill pressure should be checked from time to time as a part of routine service and maintenance. Squibs become unreliable after a time, and should be replaced, but properly maintained fire extinguishers last almost indefinitely. Pyrotechnic devices are used in some fire extinguishing systems, but valve based systems are preferred. Such is likely to be the case with air bags. Dr. Yurkin is somewhat cagey about prospects for his valves in automotive air bags, but when we met him at the last Russian Venture Fair in St. Petersburg, he did say that Daimler-Chrysler was showing "Great interest" in the idea.
As well as new markets, Ista is also looking for collaborative arrangements and possible investment, with a view to being able to expand its production facilities more rapidly.

Russian Venture Capital Association: and

Design Pointers

Valve can open fully in about 1ms
Air or gas is released in such a way that it is not required to change direction, resulting in maximum instantaneous velocity
Main market at present is in clearing blockages in bakery flour bins and hoppers, but substantial sales are also being found in line launching for rescue work, and in producing shock waves for laboratory experiments. The largest potential market, however is in the next generation of automotive air bags.