Air Entrainment – A distant cousin of Cavitation

 

Air Entrainment  – A distant cousin of Cavitation

Imagine that you are stuck in a locked room, wanting to go out but there is no escape. How much torture would that be for you? That is the amount of torture that the liquid experiences when air or vapor gets entrapped in a pump system.

Let us discuss about Airlock, how it occurs in the pump system, what are its causes and effects and 4 tips on how to control them, so that you can consider applying them in your pump system rightaway.

An air lock or a vapour lock is a restriction or complete stoppage of liquid flow caused by air trapped in pump inlet

This is because the centrifugal effect imparted by the impeller vanes onto the liquid causes the air or gas to separate from the liquid. The eye of an  impeller  is an area of low pressure, which is essential for air/gas accumulation. Eventually, the gases increases so much that air/gas bubble volume , preventing the liquid from entering the impeller. This leads to serious performance issues and also damage to pump components.

Let us understand different reasons for its existence and how to minimize or control them.

Causes :

Liquids – Aerated Liquids

It is a known fact that all liquids have some dissolved gases or air in them (E.g.: Sour Crude - Crude Oil with H2S, Water with dissolved gases).  The presence of dissolved gases could be due to the chemical reaction. For E.g.: In Singapore Waste Water Treatment Plant , A Scum (Processed wastewater ) is estimated to have up to 30% entrained air. A std centrifugal pump or even the chopper/grinder type impeller will suffer airlock if they are exposed to this type of fluid. Hence a special pump type such as side channel pump or double disc pump is required for these conditions.

Suction lift condition

For surface pumps, with negative suction requirements, insufficient suction condition can lead to formation of air pockets in addition to the piping system issues.

Tips to Control Air lock/ Air Entrainment.

1.      Min Submergence – Min Submergence is required to make sure that effects of air entrapment or Vortexing are minimized.

2.      Priming – Priming plays a vital role in any type of pump. First prime is significant for pumps be itself Priming or non-self-priming type.

3.      Pipe fittings– Right type of reducers avoids high points and thereby prevents air pockets formation in the system. For E.g.: Instead of using a Concentric Reducer that has high points in their set up, Eccentric Flat Top Reducer is highly recommended type for pump inlets.

4.      Vacuum Assisted Pump System is a better solution for systems with suction lift conditions. It is a self-sustained system that sucks the liquid from the sump during the initial prime and lets the main pump run after the priming chamber is filled up.

 

 

To understand more about Airlock , please refer to the YouTube Video Link 

You can watch it fully or can  navigate through the bookmark in the description to jump into specific sections .

 The link to  teaser of the same content can be accessed here : https://youtu.be/FGcRt1xkz74

 

Let me know your valuable comments in the comments section .

 

Regards

Karthik