I just got back to my office. Thank you all for all of your excellent suggestions. I will do some extensive testing this weekend to try and deal with some of your questions. I will post my findings on Monday or Tuesday, workload depending.
Thanks again.
Thanks waross. No cavitation noises are being heard and no cavitation erosion of the impellers has been noted. The inlet pipe is a typical bell end pointed down. We raised the wetwell setpoint to eliminate the possibility of vortices being ingested into the suction line. Again, with...
Thanks rbulsara. We cleaned the wetwell to eliminate any effects from the ingestion of grit. We verified that there were no scum blanket getting sucked into the system. It appears to be just your typical run-of-the-mill residential wastewater,+/- 97% water, 3% oganic solids,that doesn't vary...
It is great to get such good input from all of you. The downhill side of the force main gravity feeds to a sewage lift station where the water is collected in a wetwell and then pumped to its final destination, a wastewater treatment plant. The flows into the station are roughly constant on a...
Also, the line to the top of the grade is always surcharged (filled) so there is no "backing up". The decrease in discharge pressures leads me to believe that we are pumping less. My question is why? We have eliminated air entrainment as a possible culprit. The piping layout exactly follows...
Thanks Waross - The discharge shows +/- 150PSIG. As the flow drops off there is a corresponding duplicate drop-off in the discharge pressure of both pumps.
Larry P.
Thanks, Aolalde. We utilize the two pumps in series to produce the desired head required to pump over the hill. We have been monitoring both motors and pumps and everything looks fine. The inlet to the first pump is submerged and has +/- 15 feet NPSH. The discharge of the first pump is about...
Thanks, BJC. The water is discharged into a common header that charges a force main. The main crests at an elevation of +150 feet above the pump. From there it gravity feeds into a sewer main that is at the bottom of the grade a couple miles away. If we stop pumping the checkvalve on our...
Thanks, Skogsgurra. If the load were decreasing, I would expect to see the current and power factor decreasing. They appear to be remaining stable. When we are testing this system to find out what is going on, the VFD is set to minimum and maximum speed based on 60 Hertz. That way we can...
With regards to the flowmeter question: The flowmeter is of the magnetic flow meter type. If the flowmeter were malfunctioning, we would expect to see normal pump times. By comparing our flow chart recorder readings, we see that we have substanially longer pump run times that seem to indicate...
Thanks for the information. We have the ability to feed the motors with A/B Soft Starters or A/B VFD's (we have dual capability for redundancy). We have the same occurance with either starter. The load is constant, +/- 150 feet of hydraulic head, to the top of the force main. I know the power...
We have a pump station with four sets of paired centrifugal pumps operated in series to produce the necessary head for the force main application. Any set of pumps will run for a period of time and then system flow will begin to drop off from 2250GPM to 1500GPM. The weird thing is the motor...
