Pressure and Units

The pressure equivalent to the force (in Newtons) per unit of surface area (m2).
 
In the case of tubing, this is an important figure as it will determined the mechanical forces which the tubing installation is subjected to.
 
In the international system, the pressure unit id the Pascal, however this unit is very small, and so other units are often used, such as bars or the millimetres of a water column.
 
1 atm = 1 bar = 10,000 mm H2O = 750 mm Hg = 100,000 Pa
 
It must be remembered that in normal conditions, working pressure is equivalent to 1 atmosphere (owing to the layer of air which forms the Earth’s atmosphere), which means that it will always be necessary to determine as to whether the pressure values are relative or absolute. One also has to take into account that work may be undertaken in a depression – with suction - i.e. applying less air pressure, which leads to pressure values below those of atmospheric values.
 
 
Through tests in our internal laboratory and numerous years of experience in the sector of suction and industrial ventilation, we have determined that our tubing can work at overpressures of up to 3 bars and depressions (vacuum/suction) pressures of up to 0.10 bars.

 

 Dynamic and Static Pressure
 
A fluid (a liquid or gas) exercises a total pressure (Pt) on the surfaces which it is in contact with, This is the sum of the static pressure (Ps) plus the dynamic pressure (Pd).           
Pt= Ps + Pd
 
Static pressure is the pressure which fluids exercise on all the walls of the containers holding them. Fluids are formed by free molecules which move randomly and which impact against the walls of the containers which hold them, the static pressure applied is the result of these collisions.
 
Dynamic pressure is that exercised by fluid as it has a relative and perpendicular speed with respect to a surface and it is proportional to the density of the fluid and to the square of this relative speed.
 
In theory, an aeroplane which is at rest in an airport is subject to atmospheric pressure over all its surface area, which corresponds to static pressure only; an aeroplane in flight however undergoes less static pressure (at it has a reduced column of air pressing upon it as it is far above the earth’s surface) however the front part of the aeroplane (which hits the air current) withstands the dynamic pressure resulting from these colliding forces.
 
In the same manner, a tubing installation is subject to static pressure on all its walls, plus the dynamic pressure on the surfaces where it is hit by the current of air in movement.
 

 

Pol. Ind. Pla de Poliger, Sector Nord - Sau 1 -
17854 SANT JAUME DE LLIERCA (Girona) SPAIN - Tel. +34 972 26 14 67

Distributed by: Micrologic, S.L.U.

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