An air lock is a bubble of air in a liquid piping system that creates an obstacle, slowing the rate of flow or stopping it altogether. Air locks can occur in a wide variety of systems, and there are several techniques operators can use to address them. This term should not be confused with the airlock, a closed chamber separating two or more chambers from each other or allowing for movement between spaces of differing pressures.
When an air lock occurs, the bubble slowly forces its way to the top of the plumbing, because it is lighter than the surrounding liquid. Along the way, it can collect and incorporate smaller air bubbles, creating an even larger air pocket. When the pocket hits the top of the plumbing, it will prevent liquid from moving through the system, because it cannot force its way past the air bubble or push the air bubble forward in the piping. Air lock commonly occurs in fuel lines, boilers and radiators.
This situation can be accompanied by knocking and other strange noises caused by the pressure inside the symptom. One option for addressing an air lock is to change the pressure in the lines, either lowering pressure to allow the bubble to escape, or increasing pressure to allow the fluid to punch past the bubble. Another technique is to open a valve attached to a high point at the piping. Many systems include such valves for bleeding the lines to release air and allow the fluid to flow normally again.
Frequent recurrence of air lock in a system can indicate a problem with the pressure or other characteristics. A technician will need to evaluate the system to determine how and where air is getting in, and what can be done to prevent blockages in the future.
A special kind of air lock can arise in the context of fermentation vats. As beer and wine ferment, gases are generated and start to rise to the surface of the vessel, causing a rise in pressure. Without relief, the vessels would explode, generating a catastrophic mess. Leaving the vessel open to permit ventilation is not an option as the mixture can become infected or oxidized. The solution is the installation of a valve to allow carbon dioxide out, while keeping oxygen away. These systems rely on an air lock where the gas rises to the top while liquid remains at the bottom to avoid inadvertent release of beer or wine.
By Mary McMahon
Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a About Mechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.