Back pressure causing back flow.

Thanks for the info

Flow into a pump outlet will spin a pump. It becomes a water turbine.

A stuck open check valve will result in a pump spinning. This is a situation seen in duplex pump systems.

Deepwell pumps are sometimes fitted with "backstops" or one way clutches to prevent rotation in the reverse direction.

I once did a startup on a large vertical turbine pump station project at a WWTP and the GC installed the back-spin ratchets AFTER we had checked rotation on the pumps, but installed them backward. So when we were doing the witness testing, we energized the first 400HP pump into a locked rotor. To top it off (Murphy's Law), the MCC manufacturer had left one lug loose on the wire between the Circuit Breaker and the Contactor. So when the starter saw Locked Rotor Current, the mechanical force on the wires caused that one to pull out of the lug and start whipping around inside the cubicle, flashing all over the place. THAT was fun... The poor electrician with his finger on the Start button of that cubicle had to leave and go change his pants!

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

We had a submersible that ran, but stopped pumping.
With no flow, the sump level didn't drop and the controls kept the pump running.
The cause:
The pump was pumping raw sewage and so had an open impeller.
The pump was lowered down a track and at the bottom of the track it swung into contact with the discharge piping.
The pump was held in place by gravity
When originally started the force of the flow pushed the pump away from the discharge and a lot of sewage came out sideways.
There was sh.. sewage everywhere.
The solution was to trim 1/2 inch from the impeller.
Somehow the instructions got crossed up and the shop trimmed 1/2 inch from the face of the impeller instead of from the rim.
The pump would pump, just barely, but when any foreign matter struck the impeller it would trigger cavitation.
Once started, the cavitation would continue and the pump would quit pumping.
As electrical contractors we were initially blamed.
There is something wrong with the wiring. The motor isn't working.
That was probably from the same genius who had the impeller destroyed.
One of our crews made a 150 Mile one way trip to check the motor.
I don't remember who discovered the cause of the trouble, but in the end, instead of eating the cost of a service call, we were able to charge for the trip, plus a second trip to re-install the pump.

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Ohm's law
Not just a good idea;
It's the LAW!

Very useful insights. Thanks for the knowledge shared

Is the pump running forwards or backwards?
Is the motor staying energized?
What is the pump being used for.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

I used to do deep well submersibles (up to 14,000').
If it was up to us we installed both a sense circuit for the back EMF from the motor spinning as the fluid drained back and a time delay to prevent an attempted restart too soon. Some t8imes this was on the order of >30 min.
Starting a pump spinning backwards will break things.
Having a pump 'windmill', spinning forward on its own can be very hard on seals and bearings.

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P.E. Metallurgy, consulting work welcomed

Good info.. thanks