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Old 03-09-2009, 03:02 PM   #1
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Return line

I have an iwaki wmd-20rlxt and I just noticed yesterday that the return line is only 1/2"... I have one 1" corner overflow so I Am guessing that this pump is undersized for my tank. I am in the process of building a sump so should I grab a mag 9.5 and use that instead of the iwaki? My return pipe is slots cut in it and the water level is about 4" below the top of the water in the tank.
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90 gallon FOWLR 45gallong sump with Oceanic #6 skimmer. Iwaki return pump. Koralia 4 and two 300 gph powerheads.
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Old 03-09-2009, 03:10 PM   #2
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Your return pump size should be based on the it's throughput minus head loss not necessarily the size of the return plumbing. Your pump is only rated at 420gph (before head loss) and your overflow is 600 gph. Not a good thing.
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Old 03-09-2009, 05:17 PM   #3
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Quote:
Originally Posted by CaptainAhab View Post
Your return pump size should be based on the it's throughput minus head loss not necessarily the size of the return plumbing. Your pump is only rated at 420gph (before head loss) and your overflow is 600 gph. Not a good thing.
captain, the wmd-20rxlt is rated for 822 gph before headloss, I have a 4' run to the return so I am sure it is pretty close, I am just concerned with the downsized return line, is that limiting my output?
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Old 03-09-2009, 05:27 PM   #4
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You post says 20rlxt ..

Here is the info I used as a basis.

Iwaki WMD-20RLXT Pump

The RLXT type aquarium pumps are best suited for circulation only--situations where water encounters very little back pressure. The WMD pumps have American motors.
  • Flow rate: 420 gph
  • Max head: 14.1 feet
  • Amps: .45
  • Dimensions: 10.5" X 3.5" X 4.4"
  • Connections: 3/4" MPT Inlet / 3/4" MPT Outlet

Regardless, If the opening coming out of the pump is a 1/2 inch then that's what the gph rating is based on. increasing the plumbing won't increase that number. I question of we are talking about the same pump though. Your stated specs and what I found are quite different.
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Old 03-09-2009, 05:30 PM   #5
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the downsized pipe will lower the flow. As far as your overflow goes, 1" is good up to 600gph, anything less is still ok as long as it's set right. At 822gph with 4' at 1/2 in I'd say that your well under 600gph. Just be carefull not to exceed the overflow rating.
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Old 03-09-2009, 06:02 PM   #6
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Perhaps this is the pump to which you are referring:

It's the Japanese version and it's MD not WMD

Iwaki Japanese MD-20RLXT, 822 gph max. 540 gph @ 4ft. 8.2 feet max head. Magnetic Drive Circulation Aquarium Pump. 1" MNPT in x 1" MNPT out. 1/38 HP. 3100 RPM. .50 amps. 5.7 psi max. Dimensions: 8.66"L x 4.41"H x 4.17"W
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Old 03-09-2009, 08:10 PM   #7
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Quote:
Originally Posted by CaptainAhab View Post
You post says 20rlxt ..

Here is the info I used as a basis.

Iwaki WMD-20RLXT Pump

The RLXT type aquarium pumps are best suited for circulation only--situations where water encounters very little back pressure. The WMD pumps have American motors.
  • Flow rate: 420 gph
  • Max head: 14.1 feet
  • Amps: .45
  • Dimensions: 10.5" X 3.5" X 4.4"
  • Connections: 3/4" MPT Inlet / 3/4" MPT Outlet

Regardless, If the opening coming out of the pump is a 1/2 inch then that's what the gph rating is based on. increasing the plumbing won't increase that number. I question of we are talking about the same pump though. Your stated specs and what I found are quite different.
The retrun line was reduced from 1" to 1/2" on the pump. The site you were looking at must have calculated based on head loss. I checked the pump and it says 13.7 gpm which would be 822 gph. I suppose I will have to remove the reducer and upsize the return line.
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Old 03-09-2009, 09:10 PM   #8
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and on that note I'll wish you all a good night. I think I need a break :censor:
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Old 03-09-2009, 09:15 PM   #9
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Hmm I dunno, I read the badge on the pump and it says
WMD-20rlxt-115 max flow 13.7 gpm

I looked online and some sites say the wmd-20rlxt has 540 and others say 822. Some say 540 with 4' head loss. I wonder
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Old 03-09-2009, 09:25 PM   #10
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Iwaki WMD 20rlxt External Water Pump <- this site shows 540@ 4' head. If that is the case I should be fine seeing as I have a 1" overflow right?
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