Measuring O-Ring With a Caliper

The Bright and Innovative History of O-Rings

O-rings come in all shapes and sizes thanks to modern manufacturing methods. But it was not always so. These small parts, though vital to the inner working of much of our modern machinery, had a seemingly innocuous beginning.

Seal for a Light Bulb

In 1882, Thomas Edison’s patent for his light bulb showed a rubber seal where the metal and glass came in contact with each other. The rubber kept the mercury in the bulb and ordinary air out of it. Of course, light bulbs are manufactured much differently now. Although the equipment used to make light bulbs probably use O-rings to manufacture them. 

Edison got his inspiration from rubber gaskets (made of natural rubber back then) used to seal the counter-bores of piping. Edison also filed a patent in the United States for a water faucet using O-rings (an innovation still used today).

Lots of Experiments Before Widespread Use

Swedish inventor J.O. Lundberg filed a patent in his home country for an O-ring in 1896. But it was Danish-American innovator Niels Christensen who modernized the O-ring to the point where it turned into a manufacturer’s dream. 

Like many inventors, Christensen wanted to make money on his creation, which he patented in 1937 after four years of many failed experiments. He was an expert in hydraulic brake systems at the time. A terrible streetcar accident in Oak Park, Illinois, in the late 1800s motivated Christensen to invent a better braking system for these modern marvels. He patented sealed motor compressors to control the flow of compressed air for streetcar brakes. His invention was proven through the first elevated trains in Chicago in 1897. 

However, Christensen still needed a seal that would let brake pistons slide easily while blocking the flow of brake fluid. Pistons did use rubber rings, but they didn’t move very well. He tested, re-tested, and tested again. His method wasn’t very scientific. Christensen would run trials and then examine the results under a microscope to see where it was scratched. 

Finally, success. A rubber ring with a circular cross-section tested at 2.79 million strokes and return strokes at 600 psi at atmospheric pressure without leaking. His patent application did have one flaw. Christensen felt that the movement of the rubber strengthened it, but he didn’t realize that continuous lubrication, due to the action of the piston, reduced wear on the ring.

Then World War II Happened

Christensen tried selling his invention to steel mills and every manufacturer he could think of without success. Then the U.S. Department of Defense needed airplanes to fight a war overseas. The country needed tens of thousands of airplanes, and they needed to operate in extreme conditions while bringing troops home alive.

The inventor of the O-ring met engineers and officers of the U.S. Army Air Corps at Wright Field (now Wright-Patterson AFB) in Dayton, Ohio, in June 1940 with a trunkload of O-rings. Recognizing how Christensen’s O-rings worked, the men gathered that day installed some O-rings on the braking system on a well-used Northrop A-17A, the workhorse of the Army Air Corps fleet’s single-engine attack aircraft.  

The problem with aircraft braking systems is that they often broke down after a few landings because the seals would not hold up under the extreme conditions needed to bring aircraft to a halt. Repairs would be costly, and it would reduce the effectiveness of missions. In wartime, planes needed to land, reload their fuel and armaments and take off again without any problems. Stopping to make repairs on brake systems would take too much time.

Field & Laboratory Testing

Field testing of the O-rings included 88 landings of the aircraft. The brakes held up every time and didn’t fail. The same thing happened in controlled laboratory conditions. Two years later, Christensen’s invention was in every new plane that rolled off the assembly line. 

Think about the implications of the O-ring. It allowed planes to operate more efficiently on aircraft carriers, allowing them to launch more missions in shorter amounts of time. It also saved the lives of pilots in the aircraft. Further, who knows how many thousands or even millions of lives O-rings saved due to the missions flown by aircraft during the war, as well as improved safety of automobiles once manufacturers adopted O-rings in their hydraulic parts.

The one problem for Christensen: he received just $75,000 for his invention because the military bought it. His dream of getting rich didn’t happen after a lifetime of hard work. Christensen was 72 in 1937 when he patented his O-ring design.

Nineteen years after Christensen’s death, the U.S. courts awarded his estate $100,000 in 1971 for his invention. If today’s standards are any indication, Christensen’s invention is worth hundreds of billions of dollars because O-rings are in everything from automobiles and heavy equipment to medical devices and airplanes.

O-ring Surface Treatments by EZ Coating

O-rings are everywhere, and they have advanced our modern society in many ways. Now, companies have choices for O-ring surface treatments that beat PTFE in several important factors, like the coefficient of friction and abrasion resistance, for your industrial equipment, heavy machinery, and manufacturing equipment. 

Contact us for more information or if you need a test sample. We’ll respond within 24 hours.