Sump flow rate advice...

Pbrown3701 · #1 02/01/2007, 10:30 AM

So i currently have a 75gal Oceanic RR bowfront tank with a 30 gallon sump. Due to a mishap in ordering, I am running an Iwaki RLXT70 for my return. As you can imagine, this pump out pumps my overflow capacity so i have it turned down (and it also runs my skimmer and chiller). But still, the flowrate through my sump is very fast.

I'm thinking about turning the Iwaki into a closed loop pump and adding another smaller pump for the sump return. I have not had to size pumps in a while for this.

I know they recomend 20+ times turnover for in-tank flow, but what is the latest going rate for sump turnover? ANybody have a good suggestion for a submersible pump to do this? Are Mags the way to go?

30mini · #2 02/01/2007, 10:35 AM

I'd go with a mag 7 or a mag 9.5. You want probably around 10x or so turnover in your sump.

Pbrown3701 · #3 02/01/2007, 11:04 AM

can mag's be run externally? I've had problems with them adding a lot of heat in the past when used submersible.

30mini · #4 02/01/2007, 11:18 AM

you'll add more heat if you run externally!

pvtschultz · #5 02/01/2007, 12:58 PM

Quote:

Originally posted by 30mini
you'll add more heat if you run externally!

Come again? So, instead of allowing convective heat transfer to the atmospher to cool the pump (as well as the water flowing through it) you are saying that running it submerged will contribute less energy to the water than externally given all other things being equal? I'm having a very hard time with that and I do a lot of internal thermo-fluid work on the job.

Anyways, there is a trend towards minimizing sump turnover to reduce electric costs and keep concentrations of organics up to improve skimmer efficiency/efficacy. I personally run about 3x tank volume through my sump/hr. This is slightly more than what my skimmer can process which keeps it from running dry but also minimizes unneccessary electrical expenses. The same pump feeds my refugium as well.

30mini · #6 02/01/2007, 01:00 PM

mag pumps are cooled using the water that they are in. If you run one externally, I am positive that it will be hotter than if it were run submerged.

OldmillXxX · #7 02/01/2007, 01:07 PM

It might run hotter and damage the pump, but the much reduced surface area contact to the water should not heat more than the entire pump submerged. I would have to see data to think otherwise.

pvtschultz · #8 02/01/2007, 01:27 PM

My Mag 12 runs very cool externally on a CL but I run a Mag 5 submerged as a return pump. For a given amount of work done, the power supplied to the pump will be constant whether or not it is submerged or not (given there isn't a large internal winding temperature difference) so if the pump is able to cool its self by any other means than by the water it is running in, it will transmit that much less power (heat) to the working fluid. I would have a hard time believing that it will add less heat to the water submerged than mounted externally.

Anyways, I don't want to get into a techno ****ing match. Running Mags externally usually ends up in salt creep through the o-ring seal (that is why they say freshwater externally only) which is sometimes curable with a new o-ring, or just wipe it off periodically.

NickBee · #9 02/01/2007, 01:38 PM

I have a mag7 now with a 75AGA and a 30 gal sump. I would NOT recommend it at all. It's loud as heck and the GPH with a 4ft head STINKS! I'm swapping mine out soon.

Pbrown3701 · #10 02/01/2007, 02:05 PM

whoa, turn away for a second and the thread blows up.

Running externally will never add more heat than submersed. This is simple logic. If the pump is in the sump water, then yes, the pump may be cooler, but where do you think all of that heat that is being removed from the pump (to make it cooler) is going? Into the water. When you run externally, the pump may be running hotter, but some heat is being dissipated to the air.

Running submersed probablly allows the pump itself to run cooler which would prolong the life. But i'm not all that concerned with whether a 60 dollar pump runs 3years or 5.

Pbrown3701 · #11 02/01/2007, 02:07 PM

Noise is an issue to me - well, actually not to me, but my wife...

I have noticed Mags in the past also running a little loud (humming noise). Are there any submersible pumps that are not as loud (besides Quiet One - they add a ton of heat). OR an external pump that is realitively innexpensive and QUIET?

ElDiabloPollo · #12 02/01/2007, 02:55 PM

A cheap, both initial and daily, alternative to the Mag is the Quiet one pump. And as the name states, they are quiet.

And I agree with about a 3x tank turnover through the sump.

J

jlfnjlf · #13 02/01/2007, 03:10 PM

I am using a Pan World 50PX, and it was a direct fit in place of the Iwaki MD 70 RLT. it is very quiet as well.

Pbrown3701 · #14 02/01/2007, 04:53 PM

crazychicken - notice my post above that says I don't care for QUietone pumps because of the added heat. I used to use a QO6000 and it added like 4-5° to the water

douggiestyle · #15 02/02/2007, 09:15 AM

im happy with my mag 9.5. not loud. the fan on my puter is much louder. use very flexible hose to connect it. add a pad beneath it. it will be very quite.
your comment to crazychicken, you would put yourself in better light if you had made no comment. just a suggestion.

Pbrown3701 · #16 02/02/2007, 10:08 AM

douggie - do you run your mag externally or submersed?

Not sure what you mean by putting myself in a better light? I didn't mean anything by my comment other than to bring up my bad experience with the pump in the past. I hope it did not come across any differently....now that I go back and reread it, it kinda does sound like i was saying "why don't you read before commenting" which i was NOT trying to imply... SOrry if it came out that way Eldiablopollo

ElDiabloPollo · #17 02/02/2007, 10:13 AM

Its actually The devil chicken, and sorry I did not catch that you had used a QO before. In my expereince the 3000 model did not add nearly the heat that a Mag 5 or 7 would add.

Just my 2 cents.

pvtschultz · #18 02/02/2007, 11:07 AM

From my experience, the Mag 5 is probably the most vibration prone (loud) of them. I have a Mag 12 and it is dead silent. I had a QO mounted externally on a CL and it was pretty quiet, but it did have a tendancy to not start back up after a power outage. It finally melted and was replaced with the Mag 12.

Pbrown3701 · #19 02/02/2007, 01:48 PM

Devilchicken - ah yes, my spanish is suffering from lack of use since I moved from texas...

So after reading through some other threads on this topic, i think i'm going to go with something more along the lines of 3-4 times the tank volume for the sump. Supposedly, your skimmer will run more efficiently at this rate.

When I do this, I'll also convert my sump (which is empy currently) to a fuge and run my recirc skimmer feed off an overflow rather than having the return pump tee'd to it.

Anyone see any problems with this plan?

douggiestyle · #20 02/02/2007, 02:40 PM

maybe i should have kept my mouth shut this morning. my coffee had not kicked in yet. wasnt trying to stir the pot.

both are submerged. i run a mag 9.5 and a mag 7. just the tinniest of hums, enough to let you know its on. definately the quietest part of my tank.

Pbrown3701 · #21 02/02/2007, 03:02 PM

I have an old Rio3100 sitting in the garage - I wonder if this would work - Speaking of terrible pumps...