PRESSURE

PRESSURE

Scope

·         All the terms used in inspection of pressure vessel, Vacuum chamber etc. needs to know about the basic things before inspection.

Pressure

·         It is defined as the amount of force is applied on a specific area. (P=F/A)

Pressure units

·         High pressure: N/m²/ Pascal (1 atm. Pressure=14.696 psi=101.325 kPa)

·         Low pressure: 1millibar=14.5 x 10^-3 & 1 torr =19.34 x 10^-3 psi

Types of pressure

·         Gauge pressure: It is nothing but the pressure shown in the gauge. It is also calculated by difference between absolute pressure and atmospheric pressure.

·         Absolute pressure: It is the total actual pressure that is summation of atmospheric pressure and gauge pressure.

·         Atmospheric pressure: Atmospheric pressure or barometric pressure is defined as pressure exerted by the surrounding air on the earth.

·         Vacuum pressure: It is the pressure measured below the zero line or negative pressure. It is also known as differential pressure.

Relation between various pressures

 

Pressure conversion

·         1mm of Hg = 1 Torr

·         1 Inches of Hg = 25.4 Torr

·         1 Inches of water = 1.87 Torr

·         1 Feet of water = 22.39 Torr

·         1 Atmospheric = 760 Torr

·         1 psia = 51.7 Torr

·         1 Kilopascal = 7.5 Torr

·         1 Microns = 0.001 Torr

Static pressure

·         When the fluid is at rest the pressure of this fluid is known as static pressure.

·         This pressure can measured at any point on the fluid containing a vessel and this all point’s pressure will be same in all directions.

Dynamic pressure

·         Pressure measured when the fluid is in motion called as Dynamic pressure. It is the difference between stagnation pressure and static pressure.

Stagnation pressure

·         It is the total pressure that measured when the fluid is in flow condition.

Stagnation pressure = Dynamic pressure – static pressure