Instruments for Measuring Gas Pressure

1. Manometer

                                 

• it is used for measuring differences in gas or liquid pressure.
• consists of a U-tube containing a liquid such as mercury and water.
• for example, sphygmomanometer is a mercury manometer designed for doctors to measure the blood pressure of patients.
• the pressure of the gas , p, can be calculated by using the expression :

                        P = Pa + hpg

                      Pa = atmospheric pressure

                         h = height difference of liquid column

                         p = density of liquid in the manometer

                         g = Earth's gravitational field strength

2. Bourdon Gauge

• it is used for measuring very high pressure such as the pressure of steam in a boiler or the pressure of compressed gases. 
• consists of a flattened and hollow metal tube shaped like a hook.
• when a compressed gas enters the curved tube, the tube tends to straighten out thus causing the other closed end to move outwards.
• this movement is magnified by the lever arrangement which turns the cog-wheel that moves the pointer over a scale to indicate the pressure reading.