Absolute Pressure / Gauge Pressure

Dear All,

What is the word PRESSURE means? What is the diffrence betwen the Absolute Pressure and the Gauge Pressure?

Pressure is (force per unit area - Pa or psi or mb). It Starts at 1013mb (14.7psi) at sea level and falls at a non-linear rate with altitude. Losing most of its value at the lower altitudes so that at 18,000ft, for example, the pressure is halved to 506mb).

These pressure readings are absolute pressure readings. This means that if an ordinary pressure gauge is open to atmosphere it will read zero. To illustrate the point - checking a tyre pressure with it (say 30psi) the reading will be 30psi. This is called gauge pressure of the tyre. Its absolute pressure would be gauge pressure plus atmospheric pressure = 30 + 14.7 = 44.7psi absolute.

So, in general we can say that

ABSOLUTE PRESURE = GAUGE PRESSURE + 14.7 PSI

B.Regards
Ayman Shakah
Licensed Aircraft Maint. Engineer