QUESTION
Is it necessary for water lubricated vertical turbine pump line shaft bearings be immersed in water prior to starting the pump? I have a vertical turbine pump that is water lubricated and has experienced a failure in the “foot” check valve such that the pump column pipe drains down to the static water level after the pump is turned off. This exposes the line shaft bearings in the top 80 feet of the pump column to air. Prior to starting the pump the line shaft bearings are not lubricated for 5 to 10 seconds as the pump column fills with water. This pump could operate 3 to 4 times an hour during summertime water demands. Any input or experience on this subject would be greatly appreciated.
REPLIES
Valvecrazy
Yes 5 or 10 seconds of dry running will hurt the bearings. They make prelube systems that will dump a little water down the column pipe a few seconds before the pump starts. With out the foot valve you are now having to get rid of lots of air, and I’ll bet you have some real water hammer when the water finally hits the check valve at the top of the well. I am assuming you have a pressurized system since it comes on 3 or 4 times per hour. Which BTW that is about 100 times per day which is not good for anything, especially dry bearings.
As a matter of fact your foot valve probably failed from slamming 100 times per day. I have fixed lots of these with a constant pressure valve or CPV. This valve controls the flow from the pump and makes it start and stop at 5 GPM. This keeps the foot valve from slamming closed or flying open. Gentle closings and openings of the foot valve will make it last much longer.
Once the pump is started the CPV would vary the flow from the pump to exactly match the usage. This will keep the pressure steady about 10 PSI lower than the pressure switch off setting. The pump will run continuously instead of cycling on and off 100 times per day. This really saves a foot valve, as well as the motor, starter, pressure switch, and other things. Restricting the flow from the pump will lower the amperage, and it may not use any more energy than it does by cycling 100 times per day. If you use a lot of low flow, a smaller or jockey pump in the system would also help.
Either way, you are going to need to fix that foot valve.
SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=183346
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