MANOMETERS

The manometer is the simplest measuring instument used for gauge pressure (low-range pressure) measurements, by balancing the pressure against the weight of a column of liquid. The action of all manometers depends on the effect of pressure exerted by a fluid at a depth. The different types of manometers are discussed below.

1) The U-tube Manometer :-

The U-Tube is the simplest form of manometer and is used for experimental work in laboratories.

Limitations :-

In the U-tube manometer,the application of pressure causes the liquid in one leg to go down while hat in the other leg goes up, so there is no fixed referece. This tends to make the measurement of the height more difficult then it would be if one surface could be maintained at some fixed level.

2) WELL-TYPE MANOMETER :-

The Well-type manometer is widely used because of the convenience in its

requiring the reading of only a single leg.

In a single-leg instrument, high accuracy is achieved by setting the zero level of the well at the zero level of the scale before each reading is taken.

3) THE BAROMETER :-

A barometer is well-type absolute pressure gauge whose pressure range is from zero absolute to atmospheric pressure. Its readings are generally in millmeters of mercury (mm Hg), With a barometer, high vaccums are not measured. The pressure in the evacuated portion of the barometer is not really absolute zero but rather the vapour pressure of the filling fluid, mercury, at ambient temperature.

4) INCLINED MANOMETER :-

The inclined tube manometer or slant manometer is an enlarged leg manometer with its measuring leg inclined to the vertical axis by some angle. The angle of inclination is of the order of 100 .

The inclined manometer is used to measure very small pressure differences (in hundredth of an inch of water).

5) THE MICROMANOMETER :-

A micromanometer is used for the accurate measurement of extremely small pressure differences.

Wednesday, October 8, 2008

FLUIDS FOR MANOMETERS

The most common fluids for manometers are water, red oil and mercury. Water is the best fluid to use if air is the fluid to be measured and the glass length is within reasonable limits. To minimize the effects of freezing and evaporation, kerosene or antifreeze may be used.

Mercury is used when the measured fluid mixes with the manometer luid or a very long tube length is necessary, while red oil is used as the indicating fluid when it is required to read a manometer from a distant place. It is easier to read and it does not combine chemically with some fluid in a dry system.

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