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Manometer for Barometric Pressure

Imagine a balloon artist squeezing off a portion of a long balloon to make a balloon animal. Some sections of the balloon animal bulge out. It bulges because the air in its segment has been squeezed and pressurized. While our atmosphere doesn't have distinct compartments, areas of the atmosphere continually and dynamically bulge, like the balloon, creating pockets of high barometric pressure and areas of relatively low pressure. In the atmosphere, temperature and altitude cause most of the changes. Manometers are devices used to determine the degree to which air is pressurized.

Manometers
- A manometer measures atmospheric pressure or air pressure. Manometers typically use two chambers. One chamber is a sealed vacuum. The second chamber is exposed to the atmosphere. A liquid---often mercury, as used in thermometers---forms a liquid gasket between the open and sealed chambers. This allows the atmospheric pressure to affect the mercury. When barometric pressure increases, it exerts pressure on the mercury, squeezing the vacuum chamber; when barometric pressure decreases, it relieves pressure on the mercury, allowing the vacuum chamber to expand. Like a thermometer, marks are printed along the chamber, but they measure pressure not just heat.
Types of Manometers
- There are many ways to measure pressure differentials. Meriam Process Technologies, a maker of manometers, breaks them into three categories: U-tube, well type and inclined. U-tubes are like a thermometer bent into a u-shape with one end cut off and exposed to the atmosphere. A well type manometer expands on the U-tube type; on the sealed side of the tube, it has a reservoir. This allows more liquid to be displaced providing greater potential accuracy and range in measurements. An inclined manometer may just extend one arm of the manometer in a vertical but extremely narrow cylinder to increase the precision and readability of the barometric pressure. Inclined tubes are like thermometers that are leaned over with the top removed, exposing the mercury to atmospheric pressure. The incline makes pressure variances more visible in the mercury.
Altitude
- You may not give much thought to the weight of air. But air does have weight. In our atmosphere, it works just like a dam. Water at the base of a dam is pressurized by all the water sitting on top of it, just as air at sea level or below is pressurized by all the air sitting on top of it. If you rise in the atmosphere, there's less air and there's less air-mass above to pressurize the air--so, there's a corresponding decrease in barometric pressure.
Heat
- Heat doesn't just change the temperature of air; it changes the volume, too. As air is heated, it naturally tends to expand. If it does not have room to expand, its pressure increases. Because our atmosphere is full of heating and cooling cycles with day and night, there's constantly changing air temperatures, which means constantly changing air pressures. Manometers are the tools to precisely measure that pressure, wherever you happen to be.

Nature