Scheduled intervals, wear limits and the procedures for seal and bearing service. Intervals are stated in running hours rather than calendar months, because a standby pump and a duty pump age at completely different rates.
Wear limits
Impeller and wear-ring clearances govern efficiency long before they govern reliability. A clearance at twice its nominal value can cost 10% of duty-point efficiency while the pump still sounds and runs perfectly normally, which is why this is an inspection item rather than a fault-driven one.
Seal replacement
Replace mechanical seal faces as a set. Reusing one face against a new one transfers the wear pattern of the old face onto the new, and the assembly leaks sooner than either would have alone.
Bearing service
Over-greasing causes more bearing failures in this class of machine than under-greasing does. Follow the stated quantity rather than filling until grease appears — a fully packed bearing churns, runs hot and fails in a fraction of its rated life.