Let me supplement to explain the situation.
There is a check valve at pump station.
The pump doesn't have VFDs. Just on & off.
And the pipe is 16" DR25 PVC pipe.
The system is simple,one centrifugal pump station(2400gpm thru 4800gpm) and 2km foce main line(165psi rating pvc) which climbs 65m elevation and discharges at the top. The pump turns on/off more than 100 times a day.
And after 7 month operation, the force sewer line starts breaking recurrently...