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Old 10-25-2010, 06:46 PM   #1
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Mag 12 and flow rate

I've got a 125 reef that I maintain here:

Tank Journal – 125 Reef

It has a Mag 12 pump that was replaced in February and cleaned well 2 weeks ago when I replaced the sump with a 40B. I also moved it to the other end of the sup so it is now directly underneath the bulkhead. It has a vertical head of about 4.5 feet.

This is the spec sheet

http://www.dannermfg.com/instructionsheets/ZG100.PDF

Based on that spec sheet, I should be getting 950-1100 GPH out of this configuration. I am getting about 1/2 gallon every 5 seconds, which works out to less than 400 GPH. What could explain this?

I did notice that on the spec sheet it states that "1-1/2 inch inner diameter is the minimum hose size that should be used for maximum flow". This seems kind of silly, because the output nozzle is made to fit a screw-on adapter for a 1" ID hose (which is what I am using), and I thought that the larger the ID the greater the head pressure would be.

I measured the flow rate by sticking a 1/2 gallon pitcher under the overflow and timing the fill rate about 10 times and averaging the results. Initially it came out to over 5.5 seconds, but after moving/cleaning it dropped to around 5 seconds.

So what am I missing?

EDIT: the bulkhead for the return is also 1"
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Old 10-25-2010, 06:55 PM   #2
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That is interesting. I get more flow from my Mag5. Perhaps the hose you are using is collapsing on it's self? I know that if you use more rigid tubing you will not have that problem. I used a 9.5 to run my 120g reef with dual 1200gph overflows and it was T-ed to run the 55g frag tank too. Have you cleaned the impeller and housing of the pump??
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Old 10-25-2010, 07:14 PM   #3
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I would guess a kink as well.

Also, its been awhile since I have been in physics, but i seem to remember a smaller tube would lead to greater pressure but not an increase in flow?
Could be totally wrong...
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Old 10-25-2010, 07:53 PM   #4
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No Jimbo you are on the right track. Even the mag9.5 suggests using 1" thin wall PVC to plumb it for max flow.
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Old 10-25-2010, 09:31 PM   #5
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I am using 1" PVC for the overflow return but I'm guessing this is not what you are talking about. I just checked and I was mistaken, I am using 3/4" ID - 1" OD black vinyl tubing for the return. It looks like this:





So I don't think there is a problem with a kink in the hose...
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Old 10-25-2010, 09:33 PM   #6
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How would I change this though, if the bulkhead is designed for a specific size of adapter? Wouldn't I have to drill out the bulkhead?

Also, isn't the flow restricted by the riser tube for the return in the overflow anyways? Increasing the size of the tubing from the pump to the bulkhead wouldn't make much of a difference I wouldn't think.
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Old 10-26-2010, 01:21 AM   #7
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You should be getting fine flow through that...I dont' know what the problem is unless your shut off valve has some blockage
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Old 10-26-2010, 07:20 AM   #8
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i had a similar issue with a return pump i was using a while back. actually, i had a 30 breeder that i didn't have a return pump for, so i decided to use an aquaclear 70 power head. it worked well, and for a while, had plenty of power behind it. then all of the sudden i noticed the level in the 30b was a bit low, like the pump wasn't working. i inspected it and it was not dirty, nor obstructed. it just got weak.
i never could figure out why this happened. maybe the same issue.
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Old 10-26-2010, 02:36 PM   #9
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Last night I did a little bit more accurate flow test. I used a digital voice recorder and called out start/stop points, then used a stopwatch and recorded the times. Last time, I used the stopwatch and just kept it in remembered the numbers and averaged them in my head, roughly.

I opened the bypass valve and filled a 1/2 gallon pitcher over and over again.

With the pump shutoff valve closed about 1/4 of a 1/4 turn (it was operating at this level with water going over the spillway) I recorded 10 fill times and eliminated the shortest and longest times, and the remaining times averaged to 4.81 seconds per 1/2 gallon, which works out to 374 GPH

Then, I opened the pump valve all the way and let the system balance out for a few minutes, and did it again. I recorded 11 times and eliminated the shortest and longest and averaged the rest, which came out to 4.15 seconds per 1/2 gallon, or 433 GPH.

This is still less than half of the flow rate I should be getting.

I cleaned the pump out recently, it was pretty gunky though, so maybe I should try soaking it in vinegar to make sure I got it all clean. The shutoff valve has always ran fully open until after I installed the ATS, and it was clean when I put it all back together.

Here is the bulkhead and fitting for the overflow and return:



This is an old pic from before I plumbed the overflow with PVC to the sump. Just FYI. Return is on the left, and when I originally replaced the return hose I had a leak that I had to double-clamp and silicone because it was dripping about once a second. I think this indicates excessive back-pressure from the pump now that I'm thinking about it.

Thinking back now, I do remember the owner saying something about how they thought the pump had lost pressure, he said that there used to be so much pressure from the jet that you couldn't put your finger into it. That has not changed since I took over maintenance. I am now wondering if I should empty out the overflow tower and dis-assemble the entire return riser, jets, and bulkhead and inspect them for obstructions. I really wanted to add a Durso standpipe anyways, so I have more than one purpose in mind...
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Old 10-27-2010, 02:31 AM   #10
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Your output hose is WAY too narrow. Take your impeller cover to a hardware store and ask them to give you the fittings for making your pipe 1 1/2" ID hose. It's EASY. I did it for my Mag 24. The pump manual SPECIFICALLY says use minimum 1 1/2" ID hose and that is what their FLOW specs are based on. That's how they measured it and gthat's how they report it. If you're using 3/4" ID hose you have JUST cut the flow rate in HALF. Which is exactly what your 1/2 gal pitcher tests are telling you. You buy a pvc female adapter which screws onto pump outlet and opens up to 1 1/2" ID pipe. You lot of hobbyist feel they MUST use rigid pvc because thats what everyone else does. Heavy vinyl hose is easier to work with AND easier to maintain your pump, replace hose, etc. You can see inside it too and see any obstructions or clogs AND it is JUST as reliable as pvc pipe, if not more so. If you take the pump housing into home depot or ace, etc they will hook you up with 10 dollars worth of parts to double your flow.
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