ScienceIQ.com

Rossi X-ray Timing Explorer Solves Mystery of Pulsar 'Speed Limit'

Gravitational radiation, ripples in the fabric of space predicted by Albert Einstein, may serve as a cosmic traffic enforcer, protecting reckless pulsars from spinning too fast and blowing apart, according to a report published in the July 3 issue of Nature. Containing the mass of our Sun compressed into a sphere about 10 miles across, pulsars are ...

Continue reading...

RossiXrayTimingExplorer
Biology

Wetlands Top Ecosystem

Wetlands are areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season. ... Continue reading

Wetlands
Astronomy

Cosmos Provides Astronomers with Planet-Hunting Tool

If only astronomers had a giant magnifying glass in space, they might be able to uncover planets around other stars. Now they do -- sort of. Instead of magnifying a planet, astronomers used the ... Continue reading

PlanetHuntingTool
Biology

Marmaduke and the Taco Bell Chihuahua Are Cousins

You would never think Marmaduke, the enormous great dane of the newspaper cartoons, and the tiny Taco Bell chihuahua are close relatives. But the fact is, ALL dogs are pretty close relatives. ... Continue reading

Marmaduke
Geology

Hurricanes, The Basics

There is nothing like them in the atmosphere. Born in warm tropical waters, these spiraling masses require a complex combination of atmospheric processes to grow, mature, and then die. They are not ... Continue reading

HurricanesTheBasics

For Want Of An O-Ring

ForWantOfAnORingWho can forget the Challenger disaster of 1986, the culprit, a failed O-ring. But what exactly is an O-ring and how did it cause the destruction of this space shuttle? When surfaces are flat, gaskets are used to form a tight seal. How about when the machined surfaces are not flat but round? The sealing function in that case is served by an O-ring. O-rings are commonly used in hydraulic and pneumatic applications, often at very high pressures. But while an O-ring nominally serves the same purpose as a gasket, it functions in an entirely different manner. A gasket must be compressed strongly to make it fill in any inconsistent regions on flat surfaces. Compressing an O-ring in the same manner as a gasket completely defeats the functioning of the O-ring. The O-ring becomes flattened and is destroyed. Unfortunately, there are many technicians out there who never seem to learn that lesson.

The proper use of an O-ring as a pressure seal is very much a balancing act. The O-ring is designed to meet certain strength specifications and material applications, and when properly selected and applied will provide a sure seal against high fluid pressures. The trick is to apply just enough pressure to the joint to cause the O-ring material to seat against the surfaces and to stiffen against the pressure exerted by the fluid it must contain. As pressure is applied through tightening the joint, the O-ring material compresses somewhat to fill the space available to it in a specially machined groove. It becomes stiffer and unable to shift under the influence of fluid pressures, thus securing the seal. Over-tightening results in over-compression and deformation that destroys the O-ring and the seal and allows fluids to leak, possibly with dire consequences.

The restrictions on O-ring materials are more stringent. Because of the way in which O-rings function, the materials from which they are made must not be rigid materials. O-rings must be chemically inert to fluids such as hydraulic oils, organic solvents, and a variety of acidic and caustic water-based solutions. This leaves only special rubber and plastic formulations, usually silicon-based. Unlike gaskets, O-rings must be made to precision dimensions and with close attention paid to uniformity of shape. An O-ring that does not meet these requirements will certainly fail at the first opportunity. In the case of the Challenger, the cause of the failure was the temperature. On the morning of the Challenger launch, the temperature was below freezing, causing the O-rings to become hard and lose their flexibility. The result was a catastrophic leak of fuel which, when ignited, engulfed the entire shuttle in superheated flames. A devastating result due to the failure of an O-ring.