Column Manometers

Calibration of Gauges Simple liquid-column manometers... 

Those that are based on the height of a liquid column (manometers)... 

Multiplying Gauges To attain the requisite precision in measurement of small pressure differences by liquid-column manometers,... 

Modern methods of pressure measurement began as early as 1643 with the development of the mercury-column manometer by Torricelli, which are still used in some antique domestic barometers. The unit 1 Torr = 1 mmHg = 133.322 Pa (by definition exact) is a reminder of this almost outdated technique. 

Liquid-Column Manometers The height, or head, p = phg/g to which a fluid rises in an open vertical tube attached to an apparatus containing a liquid is a direct measure of the pressure at the point of attachment ancf is frequently used to show the level of liquids in tanks and vessels. This same principle can be applied with U-tube gauges (Fig. 10-la) and equivalent devices (such as that shown in Fig. 

From a hydraulics standpoint, a reboiler and column base function crudely as a U-tube manometer whose natural period in seconds is approximately V//1.3 where / is the length in feet of the liquid column. Manometer theory says that damping is increased as the liquid flow restriction is increased. There may be a connection between this and choked-flow instability for a period of 3 seconds, / = 15 feet, which is fidrly typical for industrial installations. 

Low vacuum (760-25 Torr) is the vacuum that can be achieved or measured with liquid column manometer. 

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