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 determined by using the formula PV = nRT. 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) and compare it to 96 °F (35.6 °C; 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 to 96, temperatures of 273.15 K and 308.71 K should be compared. The actual scientifically valid change in temperature from 32 to 96 °F is by a factor of 1.13 (308.71/273.15), 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 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: Scott 2.2/ 3.5/ 4.5 Air-Pak SCBA
Famous quotes containing the words effect of, effect, temperature, pressure and/or readings:
“I shall th’effect of this good lesson keep
As watchman to my heart.”
—William Shakespeare (1564–1616)
“An actor must communicate his author’s given message—comedy, tragedy, serio- comedy; then comes his unique moment, as he is confronted by the looked-for, yet at times unexpected, reaction of the audience. This split second is his; he is in command of his medium; the effect vanishes into thin air; but that moment has a power all its own and, like power in any form, is stimulating and alluring.”
—Eleanor Robson Belmont (1878–1979)
“The siren south is well enough, but New York, at the beginning of March, is a hoyden we would not care to miss—a drafty wench, her temperature up and down, full of bold promises and dust in the eye.”
—E.B. (Elwyn Brooks)
“The mother whose self-image is dependent on her children places on those children the responsibility for her own identity, and her involvement in the details of their lives can put great pressure on the children. A child suffers when everything he or she does is extremely important to a parent; this kind of over-involvement can turn even a small problem into a crisis.”
—Grace Baruch (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)