Hi Rajat,
Process flows are very hard to explain, it depends on the industry requirement. SAP can be molded accordingly. Some of the contents which are already available in SCN, please find below links.
PM - Plant Maintenance Process Flow
Standard process flow in SAP PM
Most of the places, every one suggests to use the SAP library. If you go to the link, will give you how to replace the pump in SAP
Replacing a Pump in an Operational System
Managing a Serialized Replacement Part
On fleet management, the link is shared by Chintan.
Mostly this will fall under customer service, since you lend or sale the equipment to others. Also if this is inhouse usage, you can have measurement counter to for maintenance planning.
Regards
Terence