Pressure gauge, absolute

Pressure and Vacuum. Pressure is usually designated as gauge pressure, absolute pressure, or, if below ambient, vacuum. Pressures are expressed in pascals with appropriate prefixes. When the term vacuum is used, it should be made clear whether negative gauge pressure or absolute pressure is meant. The correct way to express pressure readings is "at a gauge pressure of 13 kPa" or "at an absolute pressure of 13 kPa."... 

Any Pressure Leve) Above Atmospheric (gauge or absolute = (gauge) + (barometer))... 

For example, for a line discharging a compressible fluid to atmosphere, the AP is the inlet gauge pressure or the difference between the absolute inlet pressure and atmospheric pressure absolute. When AP/Pi falls outside the limits of the K curves on the charts, sonic velocity occurs at the point of discharge or at some restriction within the pipe, and the limiting value for Y and AP must be determined from the tables on Figure 2-38A, and used in the velocity equation, Vj, above [3]. 

The pressure units (gauge or absolute) must be consistent for all components used in determining both suction side and discharge side conditions. Most designers use gauge as a reference, but this is not necessary. 

Vacuum pressure Gauge pressure in psi (gpsi) is the amount by which pressure exceeds the atmospheric pressure of 14 psi (negative in the case of vacuum). The absolute pressure (psia) is measured with respect to zero absolute vacuum [29.92 in. (101 kPa) Hg], In a vacuum system it is equal to the negative gage pressure subtracted from the atmospheric pressure. (Gauge pressure + atmospheric pressure = absolute pressure) (1 in. Hg = 0.4912 psi of atmosphere on a product) (1 psi = 2.036 in. Hg). 

The gauge shown on the left is sealed with respect to the atmosphere and is used to measure changes in absolute pressure. The gauge on the right is open to the atmosphere and sample, and therefore it is used to measure gauge pressure. 

Vacuum and pressure measurements were all originally made compared to atmospheric pressure, or gauge pressure. The term psig (pounds per square inch-gauge) refers to this comparison. Absolute pressure includes atmospheric pressure (14.7 psi) and is called psia (pounds per square inch-absolute). For example, your tire pressure is 35 psig or 49.7 psia. Generally, unless otherwise identified, the lone identification psi refers to gauge pressure. 

Most pressure gauges give readings which are the difference between the pressure of interest and the pressure of the surrounding atmosphere. These readings are known as gauge pressures, and can be converted to absolute pressures by addition of the barometric pressure. Absolute pressures must be used in thermodynamic calculations. 

The fluid pressures referred to so far are all absolute pressures, in that a pressure of zero corresponds to a perfect vacuum. Many pressure-measuring devices give the gauge pressure of a fluid, or the pressure relative to atmospheric pressure. A gauge pressure of zero indicates that the absolute pressure of the fluid is equal to atmospheric pressure. The relationship for converting between absolute and gauge pressure is... 

The abbreviations psia and psig are commonly used to denote absolute and gauge pressure in Ibf/in.. Also, it is common to refer to negative gauge pressures (absolute pressures less than atmospheric) as positive amounts of vacuum for example, a gauge pressure of — 1 cm Hg (75.0 cm Hg absolute if atmospheric pressure is 76.0 cm Hg) may also be called 1 cm of vacuum. 

Your textbook lists five types of pressures atmospheric pressure, barometric pressure, gauge pressure, absolute pressure, and vacuum pressure. 

Gauge pressure + barometric pressure = absolute pressure. 

P = gauge air pressure in flake Pg = atmospheric pressure (absolute)... 

Absolute Pressure (psia). The sum of atmospheric and gauge pressures. Absolute pressure in a perfect vacuum is 0, and at the atmosphere at sea level is 14.7 psi (0 psig). 

Confusion about absolute pressure readings, gauge pressure readings, and vacuum pressure readings Condensation in lines to pressure indicator ... 

PRESSURE, ABSOLUTE - Pressure referred to that of a perfect vacuum. It is the sum of gauge pressure and atmospheric pressure. 

PSIA - Symbol or initials used to indicate pressure measured in pounds per square inch absolute. Absolute pressure equals gauge pressure plus atmospheric pressure. The "A" indicates that the gauge pressure is reading in absolute. 

Pressmes can be measured in environments from the near vacuum of space to more than 1,400 megapascals (MPa) and from steady state to frequencies greater than 100,000 cycles per second. Sensors that measure with respect to zero pressure or absolute vacuum are called absolute pressure sensors, whereas those that measure with respect to some other reference pressure are called gauge pressure sensors. Vented gauge sensors have the reference side open to the atmosphere so that the pressure reading is with respect to atmospheric pressure. Sealed gauges report pressure with respect to a constant reference pressure. 

P = average absolute pressure (not gauge) across the valve) is better for a gas. Why ... 

The term pressure is used throughout this chapter to mean the absolute pressure, not the gauge pressure, which is the pressure above atmospheric pressure. Absolute pressure is gauge pressure plus atmospheric pressure. Absolute temperature and temperature differences are measured in Kelvin (K). = /(°C) +... 

Gas pressure The force exerted by a gas in its surroundings. In the United States, gas pressure is commonly designated in pounds per square inch (psi). The analogous SI unit is the kilopascal (kPa). One psi equals 6.894757 kPa. The term psia refers to absolute pressure. Absolute pressure is based on a zero reference point, the perfect vacuum. Measured from this reference, the standard atmospheric pressure at sea level is 14.696 psi however, local atmospheric pressure may deviate from this standard value because of weather conditions and distance above or below sea level. Gauge pressure, designated by the term psig, is that pressure above local atmospheric pressure. Therefore, psia minus local atmospheric pressure equals psig. 

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