Plumbing – “Air Locks”

The blog Pumps – Centrifugal Pumps provided some basic information about the type of pump most commonly used in industrial cleaning equipment.  Centrifugal pumps are simple, relatively inexpensive, versatile and reliable.  However, as I mentioned in that blog, they do have some limitations.  In order for a centrifugal pump to function, liquid to be pumped must be delivered to the pump by gravity.  In pump terminology, it must have a “flooded inlet.”  The design of the pump is such that it will pump liquids but not air.  At first, this wouldn’t seem like a major issue.  The simple solution, it would seem, would be to locate the pump below that vessel that is the source of liquid and liquid should easily flow to the pump thereby flooding the inlet and all will be well as shown in the plumbing schematic below.

But, whoops, in a typical cleaning system it may not be that simple!  Let’s take a look at another plumbing schematic which, although still simple, incorporates some common features that can lead to a problem called a “air lock,” a condition in which the centrifugal pump inlet is not flooded which not only will prevent the system from circulating liquid properly but could, easily, permanently damage the pump and, in some cases, other system components if not recognized.

So you say, “OK, cool.  What’s the problem?”  Well, the problem occurs when a system as shown above is freshly filled with liquid or filled following draining for maintenance.  Once the system is drained, re-filling all of the plumbing lines may not be a simple task.  It’s not always as easy as just refilling the tank.  The potential problem is exacerbated by the fact that, since the pipes and plumbing fittings are usually opaque, there is no sure way to diagnose an air lock problem or isolate it from other potential problems that produce similar symptoms.

Let’s continue with further discussion of the problems in the next blog.

–  FJF  –