Mag 12 and flow rate

[Floyd R Turbo]

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

http://www.aquariumadvice.com/forums/f11/tank-journal-125-reef-125546.html

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"

 

[Ziggy953]

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??

 

[Jimbo7]

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...

 

[Ziggy953]

No Jimbo you are on the right track. Even the mag9.5 suggests using 1" thin wall PVC to plumb it for max flow.

 

[Floyd R Turbo]

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...

 

[Floyd R Turbo]

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.

 

[Ziggy953]

You should be getting fine flow through that...I dont' know what the problem is unless your shut off valve has some blockage

 

[mr_X]

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.

 

[Floyd R Turbo]

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...

 

[waynotcars]

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.

 

[Floyd R Turbo]

Thanks. That does make sense and I suspected that was the case.

However, it still leaves the question of the weakest link. It seems that the flow would be restricted anyways since the bulkhead is designed to take a screw-in adapter for a 3/4" ID hose. I will look at Menards (they carry the best selection of Schedule 80 adapters) to see if they have one with the same threading and a 1-1/2" hose connector.

The other issue is still the riser tube leading from the bulkhead up to the jets, this is not 1-1/2" diameter I guarantee it. So you end up with a choke point no matter what you do.

I thought about maybe finding a fitting to go on the outside of the threading on the bulkhead under the tank, however I discovered quickly that this is not a standard diameter and the only fitting that matches it is the locking nut that comes with the bulkhead. So that's not an option.

The worst-case option is drilling out a larger bulkhead on a tank in use. Not something I want to attempt

 

[waynotcars]

You should be able to find an adapter for the 1 1/2" hose to the bulkhead. It may take 2 or 3 pieces but will be possible. Again, take it to the hardware store if possible. Remember though, that the pump can only habdle what the outflow can flow. Another words, too much return flow and the tank will over flow and you'll have to valve the pump down anyway. The flow you have now just may be sufficent enough and why mess with it? I use my mag 24 solely for a closed loop system which feeds 6 outlets with a SCWD in between for a closed loop wavemaker. Too fast a flow through your sump is not always a good thing. Water movement INSIDE display tank is important, not from tank to sump amd back. Know what I mean?

 

[Floyd R Turbo]

I'm with you. Right now the tank has over 250# LR (estimated), 2 Koralia 2's and 1 Koralia 3 (or maybe the other way around - one bigger one). But that's not the issue. I am running an Algal Turf Scrubber (ATS - see that thread) and the screen needs 35 GPH/inch of screen, minimum, which equals 700 GPH. Otherwise, the algae won't get enough Iron, grows unevenly, and isn't as effective.

So I can see how I can plumb from the pump to the bulkhead, no problem. I'm still struggling with the physics / flow dynamics of a choke point in the return line. Maybe I need to look at the adapter closer, but wouldn't the ID of the adapter into the bottom of the bulkhead and the adapter going out of the top of the bulkhead still restrict the flow? Is it less of an issue since it's only a short length of the overall return path? If the riser tube from the bulkhead to the jets is smaller than 1-1/2", isn't this all moot?

Also, the tank is a 125 peninsula tank, meaning the overflow is on one end and should be plenty large to handle 900 GPH+...but I better double check that!!!

 

[waynotcars]

Well, speaking from personal experience. I just recently, like last week, went through this on my closed loop. I spent a LOT of mula on a mag 24. I plumbed it to my closed loop with 1" ID hose which went right into the SCWD (switching Current water device. From OUT of the scwd's two 1" outlets, for SOME dumb reason I adapted down to 3/4" ID pvc. Well the SCWD's switch rate depends on the flow hitting it's gears. First off, I was SO disappointed with the flow coming out of my 6 closed loop outlets. IMO it was weak as He--. Then, the rate at which the SCWD switched sides was crazy slow. I thought, man, WHAT size pump do I have to buy to get the flow I want?? Well, a few days ago my mag 24 sucked up a piece of plastic wire tie that came loose in tank and BAM there went the impeller (cheezy cheap things for the price, the impellers I mean). SO, I ordered a new impeller and I thought to myself, while this thing is down LET me plumb it RIGHT. So I want to hardware store with pump cover and said, listen man, I want to come of this thing with 1 1/2 " ID tube and go into my 1" SCWD opening. In 5 minutes the guy hooked me up with the adapters I needed. I RE-built the closed loop coming OUT of the scwd with 1" pipe instead of the 3/4" I was using. Now, granted, at the SCWD, where it goes down from 1 1/2" to 1" is a choke point BUT less of one then I had before. Well all I can says is WOW!! What a difference! The flow is INSANE! and the SCWD switches at a rapid rate and my 220 is filled with current and waves. My 1 1/2" hose from the Mag to the SCWD is about 2 feet tall. I GUESS that just that little bit LESS of restriction made ALL the difference in the world.

 

[Floyd R Turbo]

Interesting...Thanks for the description!

It sounds like, based on your description, one short choke point versus a long run of restricted cross-section produces better flow. I think I'll try switching the pump-to-bulkhead tubing first, and see if that makes a difference before doing the whole riser/jet stack...

 

[mr_X]

the output on a mag24 is 1" I.D. it makes absolutely no sense to put a 1.5" hose on a 1" threaded outlet.

 

[waynotcars]

Really? Then you should contact Danner Manufacturing and ask WHY they specifically SAY to use a minimum of 1 1/2" id hose for best flow AND that is what their flow specs are based upon? Look up their manual on web, it's there and disagree with the manufacturer and tell THEM they make "absolutely no sense". Don't bother arguing with me, argue with the manufacturer. I am SURE you know MORE then they do about their own pumps.

 

[waynotcars]

Here is the link to the PDF instruction manual for the mag 24. Please read, THEN comment

http://www.aquacave.com/Manuals/Danner-MAG24-Manual.PDFent.

 

[waynotcars]

Here is a quote from Melv's Reef.com in regard to his closed loop system he used a Mag 7 with:

What sized plumbing should I use?
The Mag pump comes with printed instructions that state to double the outlet size to determine the plumbing needed. The Mag 7 has a 1/2" outlet, and the pvc needs to be 1". If you use 1" plumbing, you'll get better flow than if you used smaller I.D. (inside diameter) pvc. Now that brings up a new problem, in that you need it to get smaller for the SCWD, and then ramp back up to larger pipe to avoid constriction. So you'll have to find "bushings" or reducers to make things work. Or use larger flexible hose: Slip on a small piece of one size on to the SCWD outlets to act like a small collar, then slip the next size hose over that, clamping it securely. Metal hose clamps can be used in dry areas, but not if the connections are submerged.

You will SEE here that he specifically says AND points to a link from Danner which says DOUBLE the outlet size for best flow.

I REALLY think people should at least TRY to do research BEFORE making comments.

 

[Floyd R Turbo]

I actually did call Danner Mfg today, and what they told me is specifically that the flow output requirement stating 1-1/2" diameter is not related to the output nozzle size, and that you do indeed need to use 1-1/2" diameter not 3/4" tubing that matches the output nozzle.