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I'm installing a new sump pump basin in a new location in my crawl space. I currently have a Zoeller M53 1/3 HP. The discharge pipe will come out the back of my house, but I want to bring the discharge to daylight near a ditch at the front of my house. So basically, the pipe will need to do a 180 from the back of the house to the front. I can use 45s to lessen the load. Unfortunately, I can't have the discharge pipe come out of the foundation in the front of the house or the side given the basin location. I also want to hide the discharge coming out of the foundation in the back of my house and behind a bush.

The picture here shows how the discharge pipe comes out of my crawl space.

enter image description here

From here, I'll need to use a 90 (or 2 45s) so the discharge goes from the back of my house to the side of my house. Then do the same so it goes out front. This will basically equate to 8 45 degree elbows and 1 90 degree elbow. There will be roughly 150' of horizontal pipe. Overall, this seems like quite a bit of load on the pump.

This picture explains what I mean. In the picture I'm just using 90s for visualization, but could use 45s if that would lessen the load on the pump.

enter image description here

My question is, why does the number of turns and horizontal distance after the downward 90 degree elbow (where the freeze guard is) matter? After the pipe enters the ground, the pipe will be sloped and gravity will help push the water to the end. It seems like after the pipe leaves the foundation of my house and goes downward, there shouldn't be any extra load on the pump.

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    If the pipe is sized and sloped such that gravity will do all the work after the pipe exits your foundation, then those additional turns don't matter. Basically you would need to size and slope it like a gutter or swale. However, if at any time that pipe is partially blocked and/or becomes "full", you would have significant friction loss due to the bends and it would affect pump performance. Also, that many bends makes the line difficult to snake/rod out, so use 45s wherever you can.
    – Jimmy Fix-it
    Jan 29, 2021 at 6:32
  • Install rodding traps at suitable points so you can clean it easily... You will need to...
    – Solar Mike
    Jan 29, 2021 at 8:27
  • @JimmyFix-it, so basically after your last incline or completely horizontal pipe (leaving the foundation in my case) the length doesn't matter? However, if it were to be clogged or something that would affect it.
    – Eric
    Jan 29, 2021 at 20:20
  • It doesn't matter as long as the pump is not pushing against back-pressure (such as that caused by friction, gravity, obstruction, etc.)
    – Jimmy Fix-it
    Jan 29, 2021 at 21:43
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    Never, ever do this in drain piping - "completely horizontal pipe"
    – Ecnerwal
    Jan 29, 2021 at 21:57

2 Answers 2

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As Jimmy Fix-it says, it's a question of whether the pump sees those elbows, and the associated pipe friction, as "dynamic head" or not.

If you have (say) a 2" discharge from the pump, but you put 3 or 4" pipe in the ground, then it's likely that the pump will never "see" the rest of the pipe, if it's properly sloped and does not freeze or clog.

If it's 2 inch pipe all the way, then it will fill up when the pump is running, and the pump will be pumping against that pipe friction. Whether or not that's a problem would depend on the pump specifications. Gravity flow with low head is quite slow compared to typical pumping rates.

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  • Thanks. Using 90 elbows and 1 1/2" diameter PVC I calculated my friction loss to be 20.1 with the Zoeller M53. With a static head of 6', this puts my TDH at 26.1 which is too high for the Zoeller M53. However, as you said, if the pump doesn't "see" the elbows or extra length of PVC after it goes underground and gravity helps take it to discharge, then perhaps the M53 will be sufficient? Alternatively, it appears that going to a 3" discharge pipe after it exits the foundation, that will also cut down on the friction loss.
    – Eric
    Jan 29, 2021 at 19:52
  • The only way that the pump will not "see" the rest of the pipe is if the rest of the pipe is sufficiently larger than the pump pipe, and properly sloped.
    – Ecnerwal
    Jan 29, 2021 at 21:59
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To support the points made in earlier answers and comments, here is a quantified comparison of flow rates for pipes with a variety of diameters.

Perhaps it can help you to pick the right diameter.

enter image description here

From: https://s3.amazonaws.com/rdcms-phcc/files/production/public/Depts/Technical/2009/AppendixK.pdf (If relying on this data, best to cross check with other sources)

Note that, when sloped, and due to gravity alone, the 3in pipe has a 3x larger flow rate than the 2in pipe.

Below the maximum rate of flow, pipe length does not matter.

If the pump produces an effective flow of less than 24GPM, then a 3in sloped at 1in/4ft will barely do, to make the length after the "IceGuard" invisible.

Any more friction from gunk and dirt, and the 3in will eventually back up, providing back pressure to the pump and reducing the flow.

For a sump pump with a discharge rate in the 30 to 40 GPM range, you'd need 4in pipe sloped at 1in/4ft.

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