What is the difference between gage pressure and absolute pressure

Every field of science and discipline has different preferences, and it is the same with various regions and organizations. At times, pressure is expressed as a depth of a particular fluid. The most commonly used are mercury mm Hg , based on its high density, and water mm H2O , based on its availability.

However, measuring pressure with a column of liquid is not precise. Density of the fluid and especially, gravity can vary in any given region. There are also other kinds of pressure units, such as, ATM and torr. The absolute pressure is measured relative to the absolute zero pressure. Absolute pressure, is pressure that would occur at absolute vacuum, or zero pounds per square inch PSI. All calculations involving the gas laws require pressure, and temperature, to be in absolute units. Conversely, gauge pressure is the most commonly used reference of pressure.

Machines like air compressors, well pumps, and tire gauges will all use gauge pressure. A mercury barometer measures atmospheric pressure. The atmosphere is able to force mercury in the tube to a height h because the pressure above the mercury is zero.

Explain why the fluid reaches equal levels on either side of a manometer if both sides are open to the atmosphere, even if the tubes are of different diameters. Figure 3 shows how a common measurement of arterial blood pressure is made.

Is there any effect on the measured pressure if the manometer is lowered? What is the effect of raising the arm above the shoulder? What is the effect of placing the cuff on the upper leg with the person standing?

Explain your answers in terms of pressure created by the weight of a fluid. Considering the magnitude of typical arterial blood pressures, why are mercury rather than water manometers used for these measurements? Find the gauge and absolute pressures in the balloon and peanut jar shown in Figure 2, assuming the manometer connected to the balloon uses water whereas the manometer connected to the jar contains mercury. Specifically, consider the smaller height to which blood must be pumped.

Pressure cookers have been around for more than years, although their use has strongly declined in recent years early models had a nasty habit of exploding. How much force must the latches holding the lid onto a pressure cooker be able to withstand if the circular lid is Neglect the weight of the lid.

Calculate the pressure you would observe in units of mm Hg if the pressure at the heart were over 80 mm Hg. Assume that there is no loss of pressure due to resistance in the circulatory system a reasonable assumption, since major arteries are large. A submarine is stranded on the bottom of the ocean with its hatch Calculate the force needed to open the hatch from the inside, given it is circular and 0.

Air pressure inside the submarine is 1. Assuming bicycle tires are perfectly flexible and support the weight of bicycle and rider by pressure alone, calculate the total area of the tires in contact with the ground. The bicycle plus rider has a mass of Skip to main content. Fluid Statics. Search for:. Gauge Pressure, Absolute Pressure, and Pressure Measurement Learning Objectives By the end of this section, you will be able to: Define gauge pressure and absolute pressure.

Understand the working of aneroid and open-tube barometers. We mainly find the absolute pressure that weather conditions change in high and low.

We are also looking for absolute pressure at the atmospheric level. If pressure above zero is observed, the absolute pressure is known. It is also called complete vacuum pressure because it applies atmospheric pressure and overpressure. Sometimes it happens that the atmosphere changes its condition constantly then we have to measure pressure in pounds per square inch absolute i. The best example of Absolute pressure is to predict weather changes. Furthermore, an example of Absolute pressure is in food packaging, gas analysis, aeronautics systems.

As the name suggests absolute complete so it is very important to measure pressure with full concentration because any wrong value of pressure measurements leads to major data errors. We hope you understand all the terms related to pressure and its main types: gauge pressure and absolute pressure. I try my best to explain all these two terms with their differences. These all terms are a part of the mechanical department.

We all see the weather measurement value and all other pressure measurements value all these measurements come from the use of these absolute and gauge pressure instruments. A gauge always needs a reference point since the reading is made with a deflection in the gauge caused by a difference in pressure. Usually, a gauge is vented, meaning it uses the pressure of the air as reference. This is why it is called gauge pressure. Since gauge pressure is measured relative to the ambient pressure, changes in the weather result in different readings on the gauge pressure.

A lower atmospheric pressure would make your tires have higher gauge pressure, whereas they would actually have the same absolute pressure.

A positive gauge pressure refers to a pressure measurement that is greater than the ambient pressure. The reference pressure may even be the standard atmospheric pressure 1 atmosphere which represents the pressure at sea level at standard temperature.