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View Full Version : Size matters--or does it? Return line may be big, but the pump inlet is small...


SkyReef
05/24/2011, 04:32 PM
So I am told: "get a bigger bulkhead and return line from your sump to your external pump." So if I upsize the sump drain from 1.0" to 1.5", and run a bigger return line from the sump to my Iwaki MD 40 RT external pump, from 1.0" to 1.5", what gain will I realize? My pump's inlet is still only 3/4", and I cannot upsize that without getting a new pump.

So the question is: will I still gain a benefit from the upgrade to 1.5" on the sump drain and the line to the pump, even if the pump's inlet is but half that size, 3/4"?

Please share your knowlege. Thanks!

sjm817
05/24/2011, 05:04 PM
Yes you will gain flow. The larger pipe has less resistance to flow. Bigger pipe = more flow.

ANGRY JOHN
05/24/2011, 06:36 PM
the bigest diffrence might be in head loss due to fittings. a 90 of a larger size will cause a lot less head pressure than of a smaller one. You will get more flow.

SkyReef
05/24/2011, 09:59 PM
Yes you will gain flow. The larger pipe has less resistance to flow. Bigger pipe = more flow.

Thanks, SJM:

So, you're saying: even though the water has to merge into 1 lane, from a 2-lane highway (the convergence of water arriving from 1.5" pipe to the inlet of the pump at .75"), the pump has a greater capacity to pump that water once it arrives because it arrived at the pump with less resistance? If so, then that is welcome news.

the bigest diffrence might be in head loss due to fittings. a 90 of a larger size will cause a lot less head pressure than of a smaller one. You will get more flow.

Thanks, John:

That's a useful perspective, a 1.5" elbow is less crammed that a .75" elbow. Yet, I think I won't even have that problem because I am gluing 1.5" SpaFlex PVC to the sump's outlet. Thus, there should be no hard 90-degree bend.

Tigé21v
05/25/2011, 05:24 PM
I may be wrong, but i think you see the most flow gain when you increase the size of your return (outlet) pipe. You have gravity working for you on your inlet side. It's on the other side you could the extra help since it's now working against gravity, and chances are, a longer pipe run with more turns.
I thought I read somewhere that Danner recommends using 1 1/2" for the return pipe on their Mags, even on the smaller sizes.

ANGRY JOHN
05/25/2011, 05:29 PM
any time you can remove resistance from intake or exhaust from a pump it will push more water. We should always look to reduce intake resistance because it will prevent cavitation, and pumps for our tanks are not designed to suck against resistance. In responce to spaflex i love the idea, i run it where ever i can, make sure to use the correct solvent type glue. christy's and weldon are both good choices.