Manometers

Manometers are used for the measurement of pressure. In a single-tube manometer, a piezometer is connected to a pipe at the point where the static pressure of the fluid is to be measured. Piezometers are suitable for fluids under measurement. In a twin-tube manometer, two tubes of equal cross-section are connected together to form a U-tube. Both gas pressure and liquid pressure can be measured by using twin-tube manometers but care should be taken for not to mix or react chemically the liquid/gas under measurement with the manometric liquid. For low gauge pressures, water is taken as manometric liquid and in all other cases mercury is advisable. We can also employ a sealing liquid as a buffer to avoid reaction. The cistern type manometer requires only one reading while measurement. For the measurement of low differential pressures arising in gas-flow metering, ring-balance manometers are used. An electric displacement transducer is used in Bell-type manometers. Some other commonly used manometric liquids are transformer oil, dibutylphthalate, carbon tetrachloride and tetraboromethane.