Fire pump is difficult to rotate, you need to repair it as follow
Shaft bending: Many fire pumps, after long-term use or shelving, the shaft will bend. At this time, straighten the shaft or replace it as required.
The running clearance between the wear rings is incorrect: When a problem occurs with the rotation of the fire pump, it is recommended to check the clearance immediately. Some fire pumps, with the accumulation of time, the running gap between the grinding rings will continue to expand. At this time, it is recommended to replace the wear ring of the pump casing or impeller. The pressure of the pipeline on the pump casing is too large: eliminate the pressure. If you do not understand how to eliminate it, consult the manufacturer directly. After removing the pressure, check again for a more complete repair.
Shaft or impeller ring wobble too much: Inspect rotating parts and bearings and replace worn or damaged parts as required.
There is dirt between the impeller and the wear ring of the pump casing : clean and check the wear ring, and replace it as required. Isolate and eliminate sources of dirt.