I've to dewater a reservoir to sea by using a wet pit mounted vertical shaft pump (axial flow), for watering the same reservoir i want to eliminate the extra pipe way and channel as there is positive head over the reservoir (sea level is 2.5 meter avove the reservoir)i am planning to use the dischrge flnge of the pump as the suction from sea to reservoir without runing the pump, Does anybody know what will happen to pump bearing wise?? Anyhow is it practible?? Please let me know about any remedies or cautions!!
Thanking you in advance.

If the pump motor is over the sea level, you have the first problem solved.

Normally the pumps have a check valve on the discharge side if it is so you must take it off.
BUT
The first to be aware is than when the water goes back the pump , the shaft will rotate in counter wise from original and the threaded parts could disassembly.

If you want to use the same pipe , use a check valve upward the pump and do a tee branch where to put valve , so when the pump is off you open this valve  and can fill again your reservoir.
Dont worry about your english , mine is not better.

And you could fit a hold back on the pump drive so that it can only rotate in the desired direction. When the flow reverses the water will go through the pump. Be careful to check how the impeller is secured to the shaft. Sometimes they are simply screwed on and flow reversal can drive the impeller off the shaft and it will foul the casing.

Check with pump manufacturer.

Discharge check valves could be replaced with an actuated valve so flow could be stopped in reverse if required.

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