Here was what I learned from such an experience : Most fire pump related parts tend to be made of aluminum — did you know that? To further add, this simply implies that they are already built to resist plenty of corrosion in their long term use, but that does not make them immune to eventual wear and tear, much more the regular need for maintenance and inspections.
And not only aluminum, but bronze, as well, is a common element used in all parts of the composition of a true fire department truck, its pump and impeller and its many other parts.
‘Sand blasting’, as many firefighting professionals have already been familiar with the term, most likely, is basically what tends to occur when you use a fire pump to pump water out regularly. Some of these more sensitive materials, like the impeller and its wear ring, are often worn down and do not withstand this regular procedure, which is why they must often be serviced by an HVAC tech. Yes, he or she is, in fact, usually trained to handle such needs (and not only cooling or heating systems alone, but likewise the parts surrounding these units, which are so often the same as those seen on a fire truck). Firemen, make sure your HVAC unit is both up to standard and ready to roll for when you need it. No emergency will ever allow you sufficient time to look into it without having been prepared beforehand. Be ready for when the need arises, and a fire must be put out.