Effect of Temperature On Pressure Gauge Readings
The pressure gauge's indicated gas pressure changes with ambient temperature. As temperature decreases, the pressure inside the cylinder decreases. The relationship between the temperature and the pressure of a gas is estimated by using the formula PV = nRT. (See Universal gas constant.) What is particularly important to understand from the formula is that the temperature is in kelvins, not degrees Fahrenheit. Consider the freezing point of water at 32 degrees Fahrenheit (0 degrees Celsius, 273.15 degree Kelvin) and compare it to 96°F (35.6°C or 308.71K; normal human body temperature is 37°C). While 96 is arithmetically three times 32, the difference in temperature from a scientific point of view is not threefold. Instead of comparing 32°F to 96°F, temperatures of 273.15K and 308.71K should be compared. The actual scientifically valid change in temperature from 32 to 96 °F (0 to 36 °C) is by a factor of 1.13 (308.71K/273.15K), not 3. If an air cylinder is pressurized to 4,500 psi at 96°F and later the temperature drops to 32°F, the pressure gauge will indicate 4,000 psi (4,500/1.13). Stated differently, a drop in temperature of 10 degrees Fahrenheit (5.5 degrees Celsius) causes a pressure decrease of about 82 psi. Failure to accurately account for the effect of temperature on pressure readings can result in underfilled air bottles, which in turn could lead to a firefighter running out of air prematurely.
Read more about this topic: Self-contained Breathing Apparatus
Famous quotes containing the words effect of, effect, temperature, pressure and/or readings:
“The effect of liberty to individuals is that they may do what they please: we ought to see what it will please them to do, before we risk congratulations.”
—Edmund Burke (1729–1797)
“What has been the effect of [religious] coercion? To make one half the world fools, and the other half hypocrites. To support roguery and error all over the earth.”
—Thomas Jefferson (1743–1826)
“The bourgeois treasures nothing more highly than the self.... And so at the cost of intensity he achieves his own preservation and security. His harvest is a quiet mind which he prefers to being possessed by God, as he prefers comfort to pleasure, convenience to liberty, and a pleasant temperature to that deathly inner consuming fire.”
—Hermann Hesse (1877–1962)
“Today’s pressures on middle-class children to grow up fast begin in early childhood. Chief among them is the pressure for early intellectual attainment, deriving from a changed perception of precocity. Several decades ago precocity was looked upon with great suspicion. The child prodigy, it was thought, turned out to be a neurotic adult; thus the phrase “early ripe, early rot!””
—David Elkind (20th century)
“The eating of a MacDonald’s meal is like the reading of Reader’s Digest—small, easily digested, carefully processed, carefully cut down, abridged. Reader’s Digest gives us knowledge that is easily compartmentalized, simplified, ideologically sound.”
—Clive Bloom, British educator. “MacDonald’s Man Meets Reader’s Digest,” Readings in Popular Culture: Trivial Pursuits?, St. Martin’s Press (1990)