Top 10 Causes Of Entrained Air

Air entrainment occurs when the fluid contains air bubbles before it is pumped. Air entrainment can also be caused when liquid from an elevated point splashes into a wet well, causing turbulence and air bubbles to form. These air bubbles can get picked up and suctioned into the pump during operation. While air entrainment in miniscule amounts can be used to combat cavitation, just 1 or 2 percent air entrainment can cause pump performance to decrease.

Result of air entrainment

As air bubbles become trapped at the pump suction, they block the flow of fluid, leading to a gradual deterioration in pump performance. As flow rate decreases, the developed head will drop off. This leads to an overall decrease in efficiency.

Risks of trapped air

Air entrainment causes increased vibration which leads to bearing failure. Entrained air can also collect in the seal chamber and cause mechanical seals to run dry. A squeal at the start the pump can indicate entrained air when seal faces run dry.

Entrained air can lead to the breaking of pump shafts as the pump may stall one second na pump the next in an endless loop. By introducing unwanted oxygen into the system, air entrainment can result in stress corrosion. It can also cause a pump to lose its prime.

The numbers speak for themselves:

  • Just 2% air entrainment can lead to a 12 % reduction in pump performance.
  • Just 4% entrainment can lead to a 40 % reduction in pump performance
  • At 10 % air entrainment, it’s quite likely your pump will stall completely.

Main causes of air entrainment:

1. Vortexing is the most common cause of entrained air. This happens to submersible pumps or pumps in suction lift applications when fluid levels in the tank or pit meets a certain level or when the static height of the fluid above the suction inlet is inadequate
2. Liquid is discharged from an elevated point into the pit or tank and free falls onto the fluid surface, dragging air into the suction line
3. Pumps and tanks had air in them to begin with and were not properly filled or vented during start up
4. Suction systems operated at a pressure below atmospheric (vacuum) can cause air to leak in at several places, (but when static, fluid will not leak out)
5. Leaky suction line
6. Mixers and agitators add air into the process
7. Air and gases purposefully injected into the fluid (such as to prevent cavitation) used in excess
8. A chemical reaction, creating air or gases
9. Improper design of suction pipe geometry/arrangement with unvented high points that will not dissipate or reduce the air and gases present.
10. The product contains entrained air, such as paper and pulp stock, as these companies often inject air in stock/slurry mixes.

If you’d like to find out more about what could be causing entrained air in your pump (and what to do about it) call our toll-free number at 1-800- 367-4180. We have experts on hand to help you choose, install, and maintain a variety of equipment.