Know the key aspects of fire booster pump systems before making any choice!
Code shouldn't allow a VFD on a fire pump system. The most important part of a fire pump systems is that it starts when there is a fire. Having a computerized and complicated VFD control the system is the least reliable part. It is a good thing there is a gasoline powered pump on the system (pictured) for back up. The gasoline powered pump is more dependable and will at least put out the fire when the VFD fails to start the main pump.
The two check valves or orifices are needed to stop any kind of water hammer when the pump shuts off, you don’t want the pressure bouncing and slamming up against the pressure transducer that could cause it to rupture and fail.
Also if a VFD is as good a control as salesmen are stating, there wouldn't be any water hammer on pump stop or start. When using a Cycle Stop Valve to replace the VFD there is never any water hammer on pump start or stop. Plus the CSV is more reliable than a VFD, and more likely to work when it is really needed. VFD's are a great tool for people who do not understand pumps. But for those who understand pumps, a VFD would be the last choice for a control system.