# Using a Bourdon gauge to measure lung pressure

##### lass practicals

An experiment to introduce the Bourdon gauge.

#### Apparatus and materials

For each student group

Bourdon gauge

'Paper Bourdon gauge' also known as 'party blow outs'

Foot pump

#### Health & Safety and Technical notes

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

You can buy party blow-outs that are silent!

#### Procedure

a 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.

b 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.

c Use the Bourdon gauge to measure the pressure obtained when the foot pump is used gently.

#### Teaching notes

1 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.

2 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 105 N/m2. This is the same as the pressure created by 1 kg supported on 1 cm2. (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.

3 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.

The experiment was safety-checked in July 2007