Centrifugal pumps are designed to move fluids, not air. When air becomes entrained in your pump system, it can lead to numerous operational issues and frustrations. If you suspect air might be causing problems in your pump, this guide will help you identify the symptoms and understand the common causes.
The Impact of Air Entrainment
Air inside a pump typically manifests as:
- Noisy operation
- Excessive vibration
- Decreased performance
Even small amounts of air can significantly reduce efficiency. According to the Goulds Pump Care Manual, just 2% gas by volume can cause a 10% drop in capacity. If you’re hearing a “gravel-like” noise during operation or noticing diminished performance, air entrainment could be the culprit.
More severe cases of air entrainment may lead to:
- Shaft breakage
- Seal failure
- Accelerated corrosion
Common Sources of Air Infiltration
Free-Falling Discharge
When liquid is discharged into a pit or tank near the pump suction line, it creates bubbles that can be pulled into the suction line. This “waterfall effect” introduces air into the system. Proper discharge line configuration can help avoid this problem.
Leaky Suction Lines
Air easily enters pumps through leaks at elbows, joints, and other connection points in the suction line. Remember: if fluid is leaking out, air is definitely getting in.
Insufficient Submergence
Submersible, immersible, or pumps in suction lift applications require minimum fluid levels to prevent vortex formation. When fluid levels drop too low, a vortex can form at the surface and extend all the way to the suction inlet, drawing air into the system.
Pre-Entrained Air in the Product
Some materials, particularly paper stock, naturally contain air pockets. While you may not be able to change the product characteristics, modifications to your pump or process can help mitigate issues. Consult with an experienced fluid process engineer for specific recommendations.
No Air Is Always Best
While the air-handling capacity varies between pump models, one principle remains universal: all fluid-handling pumps operate more effectively when no air is present. If you suspect air in your centrifugal pumps, contact our on-site engineering team for technical support.