Using a Bourdon gauge to measure lung pressure

Practical Activity for 14-16 PRACTICAL PHYISCS

Class practicals

An experiment to introduce the Bourdon gauge.

Apparatus and Materials

For each student group

Health & Safety and Technical Notes

The Bourdon gauge reads absolute pressure from 0-150 kPa (in Imperial units, 0-20 pounds per square inch).

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Procedure

Pass paper Bourdon gauges round the class and ask how they work. (The pressure inside makes the flattened tube uncoil.} Students should have one each and not share.
Fit the Bourdon gauge with a disposable mouthpiece and use it to measure excess lung pressure by blowing into a rubber tube connected to it, fitted with a disposable mouthpiece.
Use the Bourdon gauge to measure the pressure obtained when the foot pump is used gently.

Teaching Notes

This is an introduction to a direct reading pressure gauge. It should be used to measure any convenient pressures such as excess lung pressure and excess pressure produced when a car foot pump is attached to it and used gently. The toy Bourdon gauge helps to show how increased pressure straightens out the tube whose end is connected to a pointer.
The Bourdon gauge does not register zero when it is free standing but rather the zero is calibrated to register the current air pressure of about 10 ⁵ N/m ². This is the same as the pressure created by 1 kg supported on 1 cm ². (Old Imperial units are still often found on tyre pumping machines, recording a pressure of 14 to 15 pounds per square inch (psi) for atmospheric pressure.) Balancing a kilogram on the end of a finger will give a feel for the extra pressure on the finger. Extra because there is already the atmospheric pressure pressing on the finger in all directions.
A Bourdon gauge with a glass back is ideal, as this reveals the curved tube connected to the inlet, and the mechanism by which its unbending moves the needle across the dial.