So long as FWP is running smoothly with desired output, without any leakage, abnormal sound; it requires no repair or maintenance. Once any of the above points is found then it requires rectification of the fault for safety of the plant,personnel & equipment and reliability of the system. Apart from this kind of developed faults, manufacturers generally recommend certain weekly, fortnightly,monthly,bi-annually preventive maintenance :steps like, cleaning of filters, strainers, glands tightness/replacement etc for healthiness of the equipment as routine maintenance.
For any pump there should be pertformance parameters like temerature , pressure , flow rate etc these parameters should be monitored all the time in order to know the working health status of the pump. So, you should know from the pump datasheet the nominal values of these parameters and by using metering devices you can evaluate it.
The best way is to use condition-based monitoring (CBM) of the pumps during their operation. CMB monitors the health of the pumps and can identify degraded performance such as pumps overheating, flow reduction, discharge pressure degradation and so on. Sometimes, the voltage or current measurement or even use of vibration sensors would indicate that equipment degradation has occurred or that failure is about to occur.
The CBM approach is also called prognostic health monitoring (PHM) where degradation is identified proactively before failure occurs and, thus, will allow for human intervention to conduct the required equipment (such as the pumps) repair in a timely manner.