![]() ![]() Dry/non-lubricated seal face operation contributes to shortened life and ultimate failure. ![]() The unvented air also collects in the seal chamber (standard stuffing box configurations) to create air pockets that cause dry running of the mechanical seals. Vibration is frequently caused by the unbalanced hydraulic loads on the impeller due to partial air blockage. Air entrainment even at values as low as 2 to 4 percent will cause increased pump vibration, which leads directly to premature bearing failure. The flow rate will decrease, the developed head will drop off, and the efficiency will decline. Increases in air entrainment more than 1.5 to 2 percent will have immediate and deleterious effects on the pump from both an immediate performance aspect and a mechanical aspect in a protracted way.Īs air bubbles become trapped at the pump suction, they block the fluid flow, and the pump performance will drop off. Why Are We Concerned About Air Entrainment? The shorter tanks equate to lower submergence values, which then have a higher probability of creating vortices and the smaller vessels yield reduced volume and consequent reductions in transient times for air bubble mitigation. Further, the chemical process industry (CPI) and general industrial plants have renewed and are increasing financial pressure to design systems with smaller “footprints.” Filed under the heading of “unintended consequences” is the result of shorter and smaller storage tanks and process vessels. ![]() Oil and gas industries are working to pump more dual phase fluids at the wellhead and downstream, and wastewater treatment plants are using more dissolved air flotation (DAF) systems.Īdditionally, the industry is seeing an increased use of closed loop systems and a drive for less expensive, but consequently more shallow cooling tower basins. Pulp and paper companies inject air in stock/slurry mixes, especially as an increase in recycling is occurring. This issue is a rising trend and has become more common for several reasons. A thorough root cause analysis in addition to education regarding the matter will show air entrainment is a much more common pump ailment than initially believed. Poor pump performance is often confused and erroneously blamed on a multitude of symptoms other than air entrainment. However, air entrainment even in amounts of 1 to 2 percent will cause pump performance to drop dramatically. Many users will inject up to 0.9 percent air to cushion the effects of cavitation. The bubbles may change in size but typically do not collapse when running through the pump.Īir entrainment in very small amounts can actually be a good thing. The difference is that cavitation is the formation and subsequent collapse of vapor bubbles, while air entrainment is simply air bubbles that were in the process stream before the pump and will remain there after the pump. In recent months, I have been involved in four cases of misunderstood pump performance where air entrainment was determined to be the main culprit.Īir entrainment may sound like and be confused with cavitation in an operating pump. I didn’t plan on writing about air entrainment again, but recent field issues pushed me to revisit the subject. Read Jim Elsey's "Most Common Reasons for Air Entrainment in Pump Systems" here. ![]()
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