Pressure Vacuum Conversion
Measuring Pressure and Vacuum
Pressure is measured in ways that reflect how the pressure measurement is being used and the location where the pressure is being measured. A variety of techniques and devices are used for the measurement of pressure and vacuum. These are devices generally referred to as either pressure gauges or vacuum gauges. Pressure measurement is usually described in reference to atmospheric pressure, absolute pressure or gauge pressure.
Atmospheric or barometric pressure is the pressure exerted by the weight of the atmosphere and varies by altitude, location and weather. A column of air one square inch in cross-section from sea level to the top of the atmosphere weighs about 14.7 pounds. This gives the measure of atmospheric pressure as sea level a value of about 14.7 pounds per square inch. Absolute pressure is measured in reference to a perfect vacuum. Because of this, absolute pressure is equal to gauge pressure plus atmospheric pressure. Gauge pressure uses ambient air
pressure as its zero point. This means that gauge pressure is actually equal to absolute pressure minus ambient atmospheric pressure.
The manometer is one of the oldest types of pressure gauge still in common use. Manometers use a column of liquid, usually either water or mercury (Hg) to measure relative pressure. A vacuum gauge is used to measure the pressure in a vacuum, usually relative to the atmospheric pressure of the immediate surroundings.
Pressure Measurement in Process Systems
Differential pressure is the pressure measurement most frequently encountered in industrial process systems. Differential pressure is the difference in pressure between two points in a system. Differential pressure gauges will have two inlet ports, each connected to one of the two points being compared.
Pressure Vacuum Conversion Factors