Back Pressure of Pipe Plug

The macroscopic definition of pressure indicates that the pressure is a scalar physical quantity defined at any point of a system, whether it is fluid or solid. More specifically, the pressure is related to a pressing force exerted by the system on a surface S.

$P={\frac {F_{p}}{S}}$

Its unit in the International System is the Pascal, but it can be measured by other units such as bar, atmosphere, hectopascal, etc. Indeed, there is a passage which allows to pass from one unit to the other.

$1bar=10^{5}P_{a}$

$1atm=1013hP_{a}=1,013.10^{5}P_{a}$

Pressure is measured by means of sensors, such as pressure gauges, manometers, barometers and altimeters.

What is Back Pressure?

In terms of pipes, valves and pipe plugs, the Back Pressure is defined as the pressure that exists just behind a plug or a valve, it is the downstream or the secondary pressure of a plug. The back pressure is an applied pressure that pushes and forces the plug to move or slide inside the pipe. However, as the fact that the plug moves or slides inside the pipe is very dangerous, there is another definition, which describes back pressure as the pressure that the plug must withstand during the application tests.

How to Calculate the Back Pressure?

Often people confuse the inflation pressure with the back pressure of the plug. Even though they are different, the inflation pressure of a plug and the back pressure are related to each other. Thus, in order to calculate the back pressure, the inflation pressure must be defined.

To further clarify the process, once the plug is inflated with air, it applies pressure to the contact surface (L). A friction force then occurs between the surface of the pipe and the plug (Ff). This friction force can prevent the plug from sliding. Consequently, if the plug is inflated with less pressure, it can slide inside the pipe, which can be very dangerous. For this, the Friction Force has to be way greater than the Force created by the Back Pressure. Ffriction ≥ Fback

Pipe plugs

The Back pressure calculation is based on two equations;

$F_{b}=P_{b}S=\mu .r^{2}P_{b}$ and $F_{f}=kN=2k\mu .rLP_{i}+kW$

$F_{b}$: Back Pressure Force

$P_{b}$: Back Pressure

$r$: Radius of the pipe

$L$: Contact surface

$F_{f}$: Friction force

$P_{i}$: Inflation pressure

$k$: Friction of the plug

$W$: Weight of the plug

Then we got the following equation:

$F_{f}$ ≥ $F_{b}$ -> $2k\pi .rLP_{i}+kW$ ≥ $\pi .r^{2}.P_{b}$ -> ${\frac {2k.L.P_{i}}{r}}+{\frac {kW}{\pi }}.r^{2}$ ≥ $P_{b}$

Which means that the Back Pressure should be as follows

$P_{b}$ ≤ ${\frac {k.L.P_{i}}{r}}+{\frac {kW}{2}}\pi .r^{2}$

Calculating the back pressure helps to provide the adequate or the appropriate support to prevent the plug from sliding, thereby saving lives from danger.

Smart Plug

In general, all manufacturers of pipe plugs inform the end user of the back pressure that the plug can withstand. However, this value is always given for a specific type of pipes such as a clean, dry concrete pipe or a ductile iron pipe... Thus, when using the plug in another pipe or under other operating conditions, the plug will not be able to withstand the same back pressure as indicated. This will cause the plug to slide and burst, which may result in financial loss, serious injury or even death.

To this end, a Smart Plug has been invented to solve these problems and ensure that the application process runs smoothly by knowing the exact Back Pressure needed.

This program first calculates the back pressure by software, while the plug information and side condition parameters are entered into the system by an operator. Then the Smart Plug program calculates the maximum back pressure for that specific application. This Patented Smart Plug (patent N°: PCT/TR2020/050904) is invented in 2020.

External links

• https://www.cleaner.com

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