Q. The inside of a pump is rusting to the point that small rusted parts flake off. Can you recommend a process to clean rust and “cure” the interior of the pump housing to prevent rusting and not affect the quality of the water? C.W.
A. Cast irons can be “active” and rust rather quickly. If the level of rust is moderate, and it does not sound like it is very adherent, a phosphoric acid cleaner may be ideal to clean and remove the rust residue. Additionally, phosphoric acid cleaners are unique in that they can leave a deposit that is similar to that of a very simple, lightweight phosphate coating on the surface which can provide the “cure” or passive surface you are looking for. Increasing time and temperature (if possible) will accelerate the process and/or do a better job removing existing rust.