Science Experiments

Archive for the ‘Scientific Methods’ Category

A Bourdon tube is used for measuring pressures outside the range of the mercury filled Manometer. A Bourdon tube is simple and versatile. A Bourdon tube is also the basis of many types of Pressure gauge. A Bourdon tube is shown below.

In its simplest form the Bourdon tube consists of an oval section tube bent into a circular arc. One end of the Bourdon tube is sealed and free to move. The other end of the Bourdon tube is rigidly fixed and is open for the href=”http://www.science-experiments.info/Bourdon_Tube.html#”transmission of Pressure.

The Bourdon tube uses a pointer to indicate the Pressure applied to the Bourdon tube, as shown in the Bourdon tube figure. With some internal Pressure the Bourdon tube section becomes rounder and this causes it to become straighter. It is this motion, amplified mechanically, which is indicated by the gauge needle.

Figure 6: Bourdon Tube

Click here to read about Manometers and U Tube Manometer.

What is a manometer?

A Manometer is a scientific instrument used for Pressure measurement of liquids and gases.

U tube manometer

The U tube manometer is the simplest version of Manometers. A U tube manometer consists of a constant bore glass tube in the form of a long U, partly filled with a suitable liquid such as water, alcohol or mercury. A U tube manometer is shown below.

Figure 5: U Tube Manometer

How to use a U tube manometer to measure Pressure

To measure the Pressure of a fluid which is less dense and immiscible with the manometer fluid, a connection is made to one limb of the U-tube while a suitable reference Pressure is applied to the other limb. The vertical displacement z of the manometer fluid gives an indication of the applied Pressure difference Dp. If P_m is the density of the manometric fluid, P_f that of the fluid whose Pressure is to be measured and g is the gravitational acceleration, then

Dp = (P_m – P_f)gz

Click here to read about Bourdon Tube for Pressure measurement.

A manometer

What is pressure? The definition of Pressure

In a fluid system, pressure means the force acting upon and normal to unit area of the system.

What is the definition of Absolute Pressure?

An absolute pressure refers to the absolute force acting normally on unit area of the fluid system. It is of interest to note that whilst absolute pressure is always positive for a gas, some rare cases of negative absolute pressure have been found for some liquids.

What is Gauge pressure?

Gauge pressure represents the difference between the absolute pressure and the local barometric pressure. Very often, in practice, the readings obtained from pressure gauges are relative to the barometric pressure. It is important that the distinction is clearly understood as serious errors in results can sometimes be traced to this point.

What is Vacuum?

Vacuum is the amount by which the barometric pressure exceeds the absolute pressure (Le. it is then a negative gauge pressure).

Pressure Measurement

The liquid filled Manometer is a popular instrument for pressure measurement of steady fluid pressures because of its extreme simplicity and reliability. Many versions of the Manometer principle are in use.

Click here to read about Manometers and U Tube Manometer.

Click here to read about Bourdon Tube for pressure measurement.

Pressure Gauge in Science Experiments