it depends on national codes or proejct's specs. Sometimes the impeller is better to be SS than bronze. And the rpm rating is the recommended for any pump because using the pump at its maximum rpm would shorten its life cycle... hope it did u any good
The bronze impeller part is the easiest to answer. The use of bronze is because the chemicals used to treat the water will corrode an aluminum impeller, the water will rust a steel impeller, and a stainless steel impeller is about 3 to 4 times the cost of a bronze impeller with no noticable improvement in performance.
The rotation per minute (RPM) of the pump drive motor vary greatly depending on things like gallon per minute (GPM) needed in the system, head pressure of the system (the force to push the water through the piping), impeller size and pitch, etc. Some pumps may have a 1075 RPM drive motor, some may have a 1350 RPM drive motor, while others may have an 800 RPM drive motor.
The project Mechanical Engineer determines the GPM of water needed for the system based on the tonnage of the cooling coils present on the project. They then figure the length and rise of the piping needed on the project. These calculations are then submitted to the pump manufacturer who then sizes the impeller needed with the drive motor to match based on these calculations along with the voltage and amperage ratings submitted by the Mechanical Engineer.
If replacing the drive motor, it is always best to replace the motor with the exact RPM range of the motor. If it is not it can cause issues such as a loss in GPM, an increase in GPM (which can be worse than being under in flow), and can cause the drive motor to have an over design in amperage causing premature failure in the drive motor.
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