Ring of bolts shearing off!
Ring of bolts shearing off!
(OP)
We have seen a sewage pump rated at 440 litres/second with a motor of P1 = 267 kW P2 = 250 kW with the ring of bolts sheared off along the flange that connects to volute to the pumpmotor casing. We are wondering where the forces to do this sort of damage could have come from. We are finding it hard to see how a blockage could do this sort of damage and wonder wheter anyone has seen this sort of thing before? The only other clue is that the pump was recently repaired and some of the bolts could have been replaced!





RE: Ring of bolts shearing off!
International College
Naresuan University
Phitsanulok
Thailand
RE: Ring of bolts shearing off!
Normally the number and size of the bolts at that volute to motor case or motor adapter plate is many times the actual required strength to resist hydraulic forces, but not knowing more about your pump I cannot say that for sure.
Typically, excessive hydraulic forces would damage bearings quickly, tear up the motor, shafting, etc., but not be capable of shearing those bolts.
So that would leave things like wrong bolts, wrong torque, etc.
Make no mistake, sometimes hydraulic thrust forces can be huge, but the problem most often shows up in bearings and shafts.
PUMPDESIGNER
RE: Ring of bolts shearing off!
Hope this helps.
saxon
RE: Ring of bolts shearing off!
RE: Ring of bolts shearing off!
RE: Ring of bolts shearing off!
I had a similar problem a few years ago with 15 kW dry well submersibles (Raw Sewage transfer) shearing the volute/motor bolts.
In our case, the screenings in the treatment plant were removed during a plant upgrade.
This lead to severe pump blockages, which in one case put the impeller out of balance to such an extent, that the pump vibrated violently, the volute/motor bolts shook loose & then sheared.
The motor kept rotating & literally took off(only stopping when it twisted its power cable to a point were the copper wires inside sheared & cut the power to the motor).
The entire dry well flooded, as the associated wet well emptied with the help of gravity via the pump volute.
Never under-estimate what a blockage can do to a sewage pump !!
I hope this helps,
Berko
RE: Ring of bolts shearing off!