Upsizing the discharge pipe with a bigger main pump?


Old 09-18-19, 03:56 PM
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Upsizing the discharge pipe with a bigger main pump?

We moved in this house (build in 1988) last year. We soon noticed the backup sump pump (a battery powered Watchdog Special installed in 2014) always kicked in even after a normal rain, so we had the main pump (an Everbilt model) replaced with a 1/3hp Zoeller. Our basement was flood from the sump this summer in a heavy rain. Trying to troubleshoot the problem, we’ve replaced the main pump with a new 1/3hp Zoeller (just in case of a defective product), cleaned/replaced the check valves and drilled a hole on pipe to prevent airlock. We’ve checked the sump discharge pipe exit to the outdoor storm line to make sure it is not overflowing or blocked. We’ve also cleaned the gutters and downspouts and have downspout extension at least 10 feet from house. With all these done, during a recent heavy rain, while both main pump and backup pump were working the same time, they still cannot keep up the inflow so we had to manually scoop water out of the sump pit. (man that was the longest 20 minutes in our life!)

Our house is 300 feet from a pond, sits on a pretty high water table in general. When it rains, water starts to come into the sump pit very quick (about 10 minutes). We’re thinking, if we change to a bigger main pump, something like 1/2 hp Zoeller, do we need to upsize the discharge line exiting our house? The main pump and backup now have their PVC pipes (1 1/2") for about 2 feet up separately (with a check valve in each line) and then wye connect into the same discharge line (1 1/2”), which runs 5 feet vertical/up and 10 feet horizontal then exits from the house. My question is that if we replace with a bigger main pump without upsizing the discharge pipe, when both pumps are running at the same time (and they will!), could there be too much water into too small of a discharge pipe and then a big loss in flow efficiency?
Please help! Thanks to all!

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Old 09-19-19, 08:12 AM
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Temporarily disconnect the backup pump from the PVC outlet pipe, plug the end of the latter, and connect a fat (at least one inch) hose to that backup pump. See if the performance of both pumps running at the same time is improved. This will tell you if the outlet pipe is insufficient.

Check to see if water is pooling up against the foundation during those heavy rains. If so, correct that (may require regrading the land) so that puddling does not happen any more.
Old 09-19-19, 11:58 AM
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How long a run is the discharge 1 1/2" pipe? How many bends are there in the pipe? Both length and bends add to the resistance which creates back pressure and slows the output from your pumps.
Old 09-19-19, 01:32 PM
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Thank you for your help. The main pump and backup have their own pipes 2 feet up separately and then wye connect into the same discharge line. The shared discharge line runs 5 feet vertical/up then 90-degree elbows to a 10 feet horizontal line ( with a 45-degree elbow in the middle). Any further thoughts?
Old 09-19-19, 02:52 PM
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Hi AllanJ,
thanks for your help. To test this out, we need a good measure of the "performance". can't tell from pumps' working sound. how much gallons to outlet exit? need a test station? we'll figure it out.
Water was pooling up before but not anymore since we cleaned our gutters.

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