Absolute pressure equal to or below atmospheric pressure

Mercury barometer tube shown here demonstrates these measurements. Standard sea level air pressure pushes the mercury to a glass tube about 30 centimeters. In other words, barometer reads 30 Century Hg. Abs. Because of this last application, you must understand, absolute pressure.

Manometer for pressure measurement is used for all services in the mechanical refrigeration systems and sensors that remain installed in the systems for routine measurements. Unless otherwise stated, assume pressure used in the service of the work of the pressure sensor. One rises above sea level, is the pressure drops about 1 inch of mercury per 1000 feet. At a height of 1,000 feet above sea level, reading will be around 29. Hg. Abs. At 4000 feet, it would be about 26. Hg. Abs.

If the atmosphere were to disappear completely, pressure would be exerted on the surface of the mercury in the dish and reading will be 0. Hg. Abs. Absolute pressure, equal to or greater than atmospheric pressure expressed in pounds per square inch absolute. Is the abbreviated PSIA.

Using the same mercury barometer tube we used fortheln. Hg. Abs. dimension, we see that the normal atmospheric pressure at sea level is about 14.7 psi. If the atmosphere were present and all pressures were deleted, read as follows : 0 PSI. As 0. Hg. Abs. and 0 PSI mean just what they say, there is absolutely no pressure now. With 14.7 psi is 30. Hg. Abs., we can say that 1 inch is equal to approximately 2 Century Hg. Abs. By the way PSIA is used for pressure-enthalpy diagram for refrigerants will be discussed in subsequent modules.