ABSTRACT
U-tube manometers are classified into a group of devices that can measure pressure directly and absolutely. Obviously, the U-tube manometers are differential vacuum gauges that compare the known referenced pressures with the measured pressures. One limb of the U-tube manometer is connected with vacuum where pressure is measured, while the other limb is connected to a system with the known referenced pressure. At evacuation of U-tube manometers, the manometric fluids/oils may bubble intensively due to the gas desorption. Therefore, these substances are degassed thoroughly prior to the pressure measurement. Buoyant manometers are force vacuum gauges operating with liquids but designed a little differently from conventional U-tube manometers. The accuracy depends not only on the precision of the measurement of liquid levels but also on the purity of manometric liquids, temperature deviation, and other gauge parameters related to the uniformity of the tube walls.
