DC Controllable Pumps vs AC Pumps

[d2mini]

I installed GHL flow meter on my tank this weekend and it confirmed what I was expecting to see... a pretty low flow rate.
I know I have a lot of restriction in my return line, but still seems a bit disappointing.

The pump is a Vectra L1, rated at 3,000 gph max flow with zero head.
It has a 1" outlet, and I have a 1" barb connector coming out of it (barbs are restrictive) so I can use some silicone tubing, which is connected to the second barb connector which is also a 90 degree elbow, into 1" pvc. It then sizes down to 3/4" to get through the flow meter and then back up to 1". Then into the next set of 1" barbs and silicone tubing where it enters the overflow. Within the overflow it splits into two 1/2" returns.
So yes, plenty of restriction and in the end I'm getting only 600 gph running the Vectra L1 at 100%.

Even 1/2" pipe is capable of running around 1200 gph under high pressure, but dc pumps are not high pressure pumps.

This has gotten me curious... can I substantially increase my flow by either moving to a different DC pump, or dumping DC all together and moving back to an AC pump? Either way it would have to be submersible.

 

[gcarroll]

This is exactly why i said that the release of neptunes FMK (and like products), would leave a lot of hobbyist disappointed when they realized just how little flow they had. Most people don't realize how little flow they need. Your tank is awesome d2mini. I wouldn't change a thing!

 

[d2mini]

This is exactly why i said that the release of neptunes FMK (and like products), would leave a lot of hobbyist disappointed when they realized just how little flow they had. Most people don't realize how little flow they need. Your tank is awesome d2mini. I wouldn't change a thing!

haha, thanks.... yeah i knew it was bad, I could tell by the drain in my fuge.
This just confirms it with an actual number.
Right now I've got about 5x flow but I want more. Triton recommends twice that, and I would like more flow in the fuge to tumble my macro without the need to add a powerhead in there.
And I'd like more flow coming out of my returns in the display.

But regardless, I'd like to know what others are experiencing with the different types of pumps.

 

[Aaron Stone]

I would take the number that its giving you with a grain of salt. Looking at the pump curve for the L1 that puts you at approximately 15 feet of head, and unless you are pumping from the basement that means you have around 11 to 12 feet of head resistance in you plumbing, which I doubt. I would say that you are probably getting more flow than it is telling you, or there is an unaccounted for resistance in the pipe. I wouldn't blame the pump.

If there is that much resistance in the pipe, your money is better spent redoing your plumbing to lower the resistance. The pump curve is relatively flat, and dropping the head down to 10 feet is going to more than double your flow from the pump. Check your valves, ditch the barbs and hard pipe the whole thing, up the size of the two returns if possible.

 

[billw]

21.5 feet of head is only about 9 PSI. My guess is that your numbers are close. You have a lot of restriction in your return.

 

[d2mini]

I would take the number that its giving you with a grain of salt. Looking at the pump curve for the L1 that puts you at approximately 15 feet of head, and unless you are pumping from the basement that means you have around 11 to 12 feet of head resistance in you plumbing, which I doubt. I would say that you are probably getting more flow than it is telling you, or there is an unaccounted for resistance in the pipe. I wouldn't blame the pump.

If there is that much resistance in the pipe, your money is better spent redoing your plumbing to lower the resistance. The pump curve is relatively flat, and dropping the head down to 10 feet is going to more than double your flow from the pump. Check your valves, ditch the barbs and hard pipe the whole thing, up the size of the two returns if possible.

From my previous tests using the bucket method and some math, I was expecting something close to this.
Like I said earlier, the meter just confirmed what I already suspected.

The inlet under the overflow for the return line is 1" threaded.
So the only thing I can do is upsize, but.... the return and drain holes are REALLY close to each other. Not sure I could fit anything larger.
Mine is the 120, but here is a pic of Chris Kriens' 160 elos....
http://www.christopherkriens.com/share/elos/elos-230.jpg
Even on this larger tank, you can see how tight things are. I don't have whatever that empty hole is between.

The only thing I may be able to do is get rid of the barbs and replace with flexible pvc and slip/thread fittings.
Everything is so tight though.... even flex pvc may not be quite flexible enough.

But all that aside, I'm still curious about my initial question and how different pumps are affected by back pressure/restriction.

 

[Aaron Stone]

A DC motor on a pump running at max is going to have slightly better performance than an AC motor of the same size due to stator "pickup", hence the slight efficiency increase. If you replace your current 3,000 gph DC pump with a 3,000 gph AC pump its going to be pretty much the same flow rate, just a little less efficient. Reaction to back pressure and positive suction head is more a function of the impeller design and total shaft power.

 

[Aaron Stone]

Depending on you discharge nozzle design, you can change them as well for a little reduction in resistance. Larger nozzles will decrease the exit velocity of the water, but allow more flow.

 

[alton]

D.C. Pumps are not the only pumps that lose gph when pressure is applied, I once had a mag 18 on a 75 gallon tank with only a 1" overflow tube, and a 3/4" return up to 6'

 

[d2mini]

Ok, I'm going to make a parts list and see if I can replace the majority of the barb connectors.
That will at least be a start in maximizing flow.

 

[Aaron Stone]

Definitely, first to go should be that 90 barb! Keep us updated, I am really curious to see what changing out the fittings does for you, I suspect a lot, but I am also very surprised at the amount of resistance that there is in your system based on that pump curve.

 

[clownsrcool]

I hope someone does some valuable experiments with this new tool. It would be nice for someone to set up something to see just how much flow you will lose with certain popular fitting and plumbing styles so we all have actual data to go from.

 

[d2mini]

I hope someone does some valuable experiments with this new tool. It would be nice for someone to set up something to see just how much flow you will lose with certain popular fitting and plumbing styles so we all have actual data to go from.

Nothing new here, GHL has had them for years. I just never got around to getting one until now. Leak detectors have also been on my list since like 2012. LOL!
(If you're referring to the new Apex kit, they're way behind on this one.)
But yes, this will be cool... because I'll have exact before/after measurements once I make some changes. I won't be able to change just one thing at a time though.

 

[jason2459]

This is awesome. I'm looking forward to getting some flow meters in too. I'll be slapping one on my Return which is DC and my Skimmer Pump which is also DC which actually pulls over double what my return does in watts. Return pump is pulling around 55-60 watts and skimmer around 145-150 watts so it will be awesome to see the flow along with my air meter getting my air draw. I'll have a full picture of what my system is doing.

FWIW, it took me around 5 years to finally get my leak detectors back in place again which I just did this weekend. lol

 

[Drauka99]

Since you will be testing, why not a simple test with the flow meter connected close to the outlet of the pump with the line turned right back down into the sump. I am wondering if you will see the 2000 gph even then.

 

[ksed]

This is exactly why i said that the release of neptunes FMK (and like products), would leave a lot of hobbyist disappointed when they realized just how little flow they had. Most people don't realize how little flow they need. Your tank is awesome d2mini. I wouldn't change a thing!

Agreed!

 

[DBR_Reef]

Also remember that the sensor itself (I am assuming it is a turbine Hall effect censor) will also provide restriction. Without a more advanced sensor (like Doppler) it is impossible to say how much. I like to use oversized barn fittings, therefore there is no size reduction. I.e. If I want a segment of silicon, and my hard plumbing is 1", I use 1.5" barbs

 

[d2mini]

So I have the materials to replumb the section between the flow meter and the overflow. That will get rid of two barb connectors and a 45 degree elbow, replacing it all (about 16-18") with one long sweep of flex pvc.

Will be interesting to see what kind of improvement that gains me, and then this weekend I should have the coupling for the Vectra and can get rid of that section of barbs, including the 90 degree barb.

So it will be all 1" from the pump to the overflow, except for that short section of 3/4 through the meter.

 

[jason2459]

Thanks Dennis. I'll be interested to see what the flow rate is after the swap out. I'm guessing the barbs are a big factor and will help the most to get rid of.

Does GHL have a 1" or bigger meter? The 3/4" meter will reduce the flow a noticeable amount. Its like putting on a valve and closing it a quarter of the way.

 

[d2mini]

Thanks Dennis. I'll be interested to see what the flow rate is after the swap out. I'm guessing the barbs are a big factor and will help the most to get rid of.

Does GHL have a 1" or bigger meter? The 3/4" meter will reduce the flow a noticeable amount. Its like putting on a valve and closing it a quarter of the way.

3/4 is the largest.
I didn't notice much difference in flow when I installed it. If it made a big difference I would have had to make a good adjustment to my drain valve.