Pump Questions for a 6-inch Recirc Skimmer

[pescadero]

I'm putting together plans for a DIY skimmer and I'd like to ask for advice about selection of the recirculating pump.

My display tank will go upstairs, and a skimmer and sump system will be located almost directly beneath it in the basement (under a staircase by the laundry). The skimmer will be fed by gravity from the overflows from upstairs.

Because the skimmer will be located out of sight in a utility area, I have the luxury of making it tall to increase its efficiency. My plan is to use a single chamber counter current design, with a reaction chamber that is made from a 4 to 5 foot section of 6-inch PVC pipe. Inflow/Outflow will be made from large diameter PVC pipe (maybe 1.5 to 2 inch) to allow low impedance flow through the circuit.

The questions that still remain unanswered for me relate to the air injection & recirculation sections of the skimmer. I'm not sure what air injection methods are best, though I have been leaning toward the idea of the DIY venturi valve that's made with a stepped drill bit, like DIY PVC Pipe Venturi on randystacye's site.

Perhaps the biggest unsolved variable in the skimmer plan relates to the recirculation pump. As I understand recirculation pumps, the pressure head that the pump has to work against amounts to : A) the height difference between the pump's inlet and outlet (ie: is not related to the height of the vertical water column in the skimmer), and B) the amount of resistance to flow that's imparted by the outlet restriction (venturi valve).

Because the inlet/outlet height differential in "A" above isn't very great, I would think that the height of the water column wouldn't play a significant role in pump selection for a gravity-fed recirculating skimmer. I was thinking that the impedance to outflow imparted by the venturi valve would be the primary determinant of pump selection, by determining the load impedance imparted on the pump. Obviously, oversizing a pump would burn-up an expensive pump.

Is there any good data available for aquarium pumps related to the pump's "work" performance as a function of load impedance (afterload)? Obviously, too little pump would not be a good thing, but then too much pump wouldn't be a good thing either. It might be even worse.

Another question I'd like to ask is about heat dissipation in pumps that have outlet restrictions. Is it better to use submersible pumps located in the sump for these sorts of applications, to limit the afterload-dependent heat buildup and extend pump life?

Thanks for any insights that you might have!

[ClayWagner]

Just use a Sedra, Eheim, or Ocean Runner for the recirc and go ahead and get the venturi for it...don't skimp the venturi for a DIY one (their cheap!). Are you saying that the recirc pump effects the height of the skimmer? I will soon be in the process of building a octagon acylic recirc with the same in line as you describe...It was my understanding that the height of the output will effect the water level in skimmer. I don't The pumps input/output doesn't have to be too far away...even with a very tall skimmer. You see in other monster DIY's that the input/output of the pump are close together at the bottom. The recirc is mainly for air input. And water level is very important in a skimmer so you might want to add a gate valve on the end of that output.

[pescadero]

Originally posted by ClayWagner
Just use a Sedra, Eheim, or Ocean Runner for the recirc ...

in my understanding of things, brand isn't as important as pump operating parameters in selecting the right pump for the job, so i'm trying to find engineering data. (i like math)

...and go ahead and get the venturi for it...don't skimp the venturi for a DIY one (their cheap!).

I was looking at some of the better DIY designs. Some of the DIY designs are capable of pulling HUGE amounts of suction on the air intake, which seems to obviate the need for the commercial venturi valves. Since the commercially made venturi valves can be had for $20+S/H, its not painful to change from one to the other if the situation warrants it.

Are you saying that the recirc pump effects the height of the skimmer?

my impression is that it should not play the primary role in determining water column height. height of the skimmer does relate to skimming efficiency, so if you're looking for a high efficiency skimmer the taller designs tend to be more efficient because of increased dwell time in the circuit. WRT to the recirc pump effecting height, I don't think that there's a direct relationship, other than the volume of air that is suspended in the chamber at any given point in time. i guess a larger pump that introduces more air could effect water column height by increasing the total volume of water plus air in the reaction chamber, but that isn't what i was referring to. you should still be able to control the level by adjusting the outlet standpipe.

It was my understanding that the height of the output will effect the water level in skimmer.

the height of the input will play a role in determining water level, as will the height of the siphon break in your exit orifice. most people use an adjustable output arm to control the water level. at least that's my take on the situation.

The pumps input/output doesn't have to be too far away...even with a very tall skimmer. You see in other monster DIY's that the input/output of the pump are close together at the bottom. The recirc is mainly for air input. And water level is very important in a skimmer so you might want to add a gate valve on the end of that output.

it is my understanding that the recirculation loop's input/output can be mounted close together. doing that would also tend to minimize the differential height's contribution to the outlet pressure head. doing that would conceivably remove the "A" component to the pressure head calculations that I had mentioned earlier.

i'm not sure that i understand the benefit of placing a gate valve on the output of a skimmer to control water level. i would think that this would be a recipe for flood/disaster. to my knowledge, the only safe way to control column height is via a LOW impedance method like the adjustable standpipe so that input can never exceed output, which would back-up the drain lines in the feeder system.

[RandyStacyE]

Here's a similar thread:
http://archive.reefcentral.com/forum...readid=1253875

In that thread 'hahnmeister' suggested a Quiet One 3000.

[ClayWagner]

I'm also in question of building it out of PVC or acrylic... I could save a lot by doing PVC and my bud's a fountain builder and has everything I'd need. I'm also definately putting the skimmer on the side of the tank and stand because I only have 24" under the tank to work with. I was thinking an 8" PVC for the body the reduce to a 6" for bout 5-6" and then some conical shape (heard a thread about some floor drain) to about 8" of 3" tubing. Should the input/output be at about the same level for drilling input/output tubing max height? How long should the 8" tubing be? What do you use for a bottom on that?

[pescadero]

Randy, thanks for pointing that out. FWIW I have been following that thread, but I didn't see any objective data that was particularly helpful in answering my question about pump selection. In the absence of either data or an explanation as to why different people like different pumps, I guess I just have to take the pump recommendation on faith.

I didn't want to hijack that other person's thread with my questions that weren't germane to his project; I also couldn't tell if he was using a gravity fed input (like mine) or not.

What type of pump did you use in the 6-inch DIY skimmer on your web site? was that the Gen-X 2400? Do you have any feedback that you think would be helpful, considering that I'm looking at building a similarly sized skimmer with the DIY venturi from your site?

[draleigh]

i used a GenX NW pump, but i think if it stops i will be using an OceanRunner. Keep us updated and post some pics once you get it going

[pescadero]

I've been doing some reading, and one thing I've noticed is that there seem to be a lot of
anecdotal reports of the Quiet One 3000 being difficult to restart after a power outage.

I don't know if that is a common problem with all magnetic drive pumps or if its more of a problem with the Quiet One 3000. One thing that I have noticed though -- difficulty starting after a power-off is a huge problem with my Marineland Penguin 550 powerhead. It might take 10 tries at unplugging it and plugging it back in to get it to start up again.

Is this a common problem with all magnetic drive powerheads and pumps? Or is my Penguin just worthless? For a protein skimmer, I'd really prefer to use a pump that won't have trouble restarting if the power should cycle off/on. I'd much prefer a pump that is reliable, and something that I don't have to worry about checking every time that the power goes out. If trouble restarting is truly a problem with the Quiet One 3000, then it would be worth the money to buy a better pump.

Anyone?

[pescadero]

Randy, I just noticed that you used the Gen-X 1500 on your 4-inch DIY skimmer and the 2400 on your 6-inch DIY skimmer. Can you comment on the suitabiity of either pump in your skimmer applications? Thanks.


draleigh, not to worry -- I'll be sure to post some pics once I have the skimmer up and running.

[shelburn61]

Startup problems are common to the QO and oceanrunner pumps. Both are nice pumps, but from what I have read on RC (I'm no electrical engineer) they don't have the startup torque of some others...

The Gen-x 4100 might work well for you on that tall a skimmer, but the pumps above and the lagunas (maybe the 1500 or smaller ?) are much quieter and better quality. Check Hahnmeister's "red dragon..." thread.

Also, I have an extra pvc union that fits 4.5" tube if you need a connection for the neck. I'll sell cheap...

[pescadero]

I guess I'm missing someething. It seems that people are inclined to recommend bigger pumps on taller skimmers. My understanding of the situation is that the outlet impedance is determined solely by the size of the venturi orifice. the amount of bubbles that you generate in a 6-inch pipe should remain constant, regardless of the height of the reaction chamber. because taller skimmers are more efficient, theoretically you should be able to use a smaller recirc pump on them instead of a bigger one. yet the bias seems to be that everyone wants to use bigger pumps on taller skimmers.

[RandyStacyE]

Originally posted by pescadero
Randy, I just noticed that you used the Gen-X 1500 on your 4-inch DIY skimmer and the 2400 on your 6-inch DIY skimmer. Can you comment on the suitabiity of either pump in your skimmer applications? Thanks.


draleigh, not to worry -- I'll be sure to post some pics once I have the skimmer up and running.

The GenX-1500 seems to work pretty good for that small 4" skimmer. I haven't even felt the need to mesh mod that pump yet.

I went with that pump ONLY because it was easy to plumb and was inexpensive ... that's it. I would have preferred to use an Octopus pump, but from what I remember it didn't have NPT threads.

The #1 reason I do not like the GenX-1500 is because when I unplug it or if the electricity goes out ... it will not fire up on its own most of the time. The pump just sits and studders like piece of junk. When I blow into the venturi hose it fires right up every time.

One time the electricity flickered out and back on at my house. I came home from work to find that the pump was sitting there studdering for hours and hours ... all day long. I would have to suggest NOT using the 1500 for this reason ... IF ... all of the 1500s have this problem (I have no way of knowing).

[RandyStacyE]

I have to admit that the 6” DIY skimmer I made was a stab in the dark. I was trying to mimic the EuroReef Model CS135/ RS135 which was way over rated for a 55 gallon tank.

I originally wanted to mimic the dimensions as much has humanly possible, but when I found one foot of 2” clear PVC dirt cheap and found that it fits the drain fitting perfectly I went with the 2” neck not knowing any better. I do wish that I went with a 3” neck considering the ER has a 3.5” neck.

Besides the neck diameter it seems to me to be an excellent skimmer. There are much more elaborate designs out there but I made mine with the intention of keeping it basic, easy to build, and most of all cheap.

I somewhat recently purchased a Dwyer air meter to see how much air all of my skimmers were pulling. I get a real jumpy reading so I don’t know what to make of the results.

GENX-2400:
I appear to be getting 5-9 l/min (10.59-19.07 SCFH). The little ball hovers at around 5 l/min then jumps up to 9. I’ve been told that this is likely due to the venturi design … the air draw is unstable causing the pump to suddenly pull in a ton of air then choke therefore dropping down in air draw. I believe this could be true … it sounds reasonable.

I decided to disconnect the pump from the skimmer to eliminate head pressure as a factor and I am getting a steady 9 l/min (19.07 SCFH). This leads me to believe that this pump would work MUCH better when put to use as a recirc pump … obviously the skimmer should work better too. Now if I used a 3” neck it should work even better yet.

GENX-1500:
I’m getting about 2.5-3 l/min (5.3-6.36 SCFH).

Honestly I haven’t spent much time at all experimenting with venturi dimensions. I do know that the venturi designs shown on my web page do work, but they can also be improved upon with some minor changes to show much better results.

I do know that prefab venturis that come with skimmers are not always the best venturi for that pump. You’ll notice that the next size larger pump likely comes with the identical size venturi too. A manufacturer typically picks a size/shape, injection molds them, and spits them out by the thousands. It would be cost prohibitive to have a scientifically engineered venturi optimized for each pump even though the skimmer would work better as a result. That’s what I like about DIY venturis; make them the way you need them to be.

[pescadero]

Originally posted by RandyStacyE
The #1 reason I do not like the GenX-1500 is because when I unplug it or if the electricity goes out ... it will not fire up on its own most of the time. The pump just sits and studders like piece of junk. When I blow into the venturi hose it fires right up every time.

Thanks, Randy. That's exactly the kind of information that I'm looking for. I'd rather spend extra money on a pump that's more reliable, so I don't have to worry about checking it all the time.

[RandyStacyE]

Originally posted by pescadero
Thanks, Randy. That's exactly the kind of information that I'm looking for. I'd rather spend extra money on a pump that's more reliable, so I don't have to worry about checking it all the time.

I wouldn't even consider a pump that small for a tall skimmer or any skimmer 6" in diameter.

I don't know if I'd use the 2400 on such a large skimmer. I think you could use a bigger pump. The 4100 probably wouldn't be a bad idea, but some just don't like the GenX

[pescadero]

Originally posted by RandyStacyE
[B]I have to admit that the 6” DIY skimmer I made was a stab in the dark. I was trying to mimic the EuroReef Model CS135/ RS135 which was way over rated for a 55 gallon tank.

I originally wanted to mimic the dimensions as much has humanly possible, but when I found one foot of 2” clear PVC dirt cheap and found that it fits the drain fitting perfectly I went with the 2” neck not knowing any better. I do wish that I went with a 3” neck considering the ER has a 3.5” neck.

well, it looks like a pretty nice stab in the dark.

i followed your lead and picked up one of those 6-inch multi-way floor drains at Lowe's. i had been thinking about a 2-inch neck instead of a 3-inch neck. what is it about the larger diameter neck that you think would be more appealing?

i noticed that you have mentioned cutting the 2-inch fitting off of the floor drain to adapt it to a 3-inch neck. i'm not sure that the modification is really necessary, as a 2-inch PVC pipe will insert into the fitting, while a 3-inch PVC pipe will wrap around it. no modifications necessary.

Besides the neck diameter it seems to me to be an excellent skimmer. There are much more elaborate designs out there but I made mine with the intention of keeping it basic, easy to build, and most of all cheap.

that's my objective as well. inexpensive, easy to service, and in my case, tall to make the skimmer extra efficient.

[pescadero]

Originally posted by RandyStacyE
I wouldn't even consider a pump that small for a tall skimmer or any skimmer 6" in diameter.

I don't know if I'd use the 2400 on such a large skimmer. I think you could use a bigger pump. The 4100 probably wouldn't be a bad idea, but some just don't like the GenX

well, smaller pumps are some of the things that i've been thinking about. here's why: if you make the skimmer short enough to fit under a display tank, to obtain a reasonable dwell time you have to resort to extreme water agitation. you have to hammer the reaction chamber with lots of bubbles being thrashed about by a powerful pump, and those bubbles have to get sucked back into the pump over and over again, and you end up having extremely turbulent flow. with a lot of (excessive) turbulence, i thin you get to the point where turbulence inhibits fractionation.

in contrast, if you go to a taller reaction chamber you can increase the dwell time just by having a tall column. you don't need as much turbulence, you just need air. then you can get by with a smaller pump that uses less power, you have more laminar flow, and you have naturally longer dwell times.

in some respects, i think that people have been focusing the design criteria on methods of extreme agitation in an effort to make up for the fact that most of the skimmers are really short in stature and suffer from short dwell times. i'm thinking that if you move toward a design that has a naturally longer dwell time, you don't have to be so heavy handed with the pump, and you can let the height of the column do the work for you instead of using lots of electricity and a bigger pump to accomplish the same goal.

well, its a hypothesis anyway... it would be interesting to know if anyone has already done this sort of experiment.

[shelburn61]

Originally posted by pescadero
I guess I'm missing someething. It seems that people are inclined to recommend bigger pumps on taller skimmers. My understanding of the situation is that the outlet impedance is determined solely by the size of the venturi orifice. the amount of bubbles that you generate in a 6-inch pipe should remain constant, regardless of the height of the reaction chamber. because taller skimmers are more efficient, theoretically you should be able to use a smaller recirc pump on them instead of a bigger one. yet the bias seems to be that everyone wants to use bigger pumps on taller skimmers.

No, this theory doesn't work because a recirc skimmer is not a true closed loop. A taller water column in the skimmer puts more backpressure on the air inlet/ "venturi". Therefore, you must either use a larger pump with more "suction" or forcefeed air into the pump to get the same air draw as in a shorter skimmer.

A good thread:
http://archive.reefcentral.com/forum...readid=1133413

[ClayWagner]

I always felt that you would need a larger/more pumps for taller skimmers because as the bubbles travel up..they begin to form back together. Pescadero, I plan on doing the 8" recirc as well, we should get this design together and come up with the best plan. I've been looking into Sedra's and Ocean Runners and have seen many great reviews for recirc pumps. What kind of venturi do you plan on using? Or will you use an air inductor? You going to mesh/needlewheel?

[RandyStacyE]

Originally posted by pescadero
well, it looks like a pretty nice stab in the dark.

i followed your lead and picked up one of those 6-inch multi-way floor drains at Lowe's. i had been thinking about a 2-inch neck instead of a 3-inch neck. what is it about the larger diameter neck that you think would be more appealing?

i noticed that you have mentioned cutting the 2-inch fitting off of the floor drain to adapt it to a 3-inch neck. i'm not sure that the modification is really necessary, as a 2-inch PVC pipe will insert into the fitting, while a 3-inch PVC pipe will wrap around it. no modifications necessary.


that's my objective as well. inexpensive, easy to service, and in my case, tall to make the skimmer extra efficient.

The reason for a 3" neck is to allow the skimmer to handle much more air more effectively. A 2" neck will tend to skim more on the wet side because the bubbles are pretty much forced to be driven out of the neck easier.

This is going to be hard to describe A larger diameter allows more bubbles to accumulate in the neck, be pushed up slower, more crud-to-bubble ratio, and with more air introduced it just skims dryer. Think of it this way … if you had the chimney that was narrow the smoke would just fly straight through in comparison to a wide/fat chimney where more smoke could slowly billow through.

When it comes to modifying the drain fitting for a 3” neck it would be better to cut off the 2” receptacle instead of sliding a 3” pipe over the receptacle. Cutting it off would open the hole to a full 3” opening without restriction.

[RandyStacyE]

Well that drawing is a tad inaccurate, but basically you'd be opening up the drain fitting to the same ID of the 3" neck.

[RandyStacyE]

pescadero ,

Whey you say "you don't need as much turbulence, you just need air". Actually you want as much air as possible basically by using the pump that will provide you with the most air. Now from what I understand there’s like a limit to how much air a 6” skimmer can consume. Hahnmeister explained this to me on a couple occasions, but I can’t find the thread Basically you want a pump that produces air well, with it will always come water flow, but the skimmer should handle it just fine. It’s more the air-to-water ratio to be concerned with as far as the pump is concerned. I believe Hahnmeister mentioned to me that the 4100 would be way too big of a pump for my skimmer because the 2400 will produce plenty of air for a 6” skimmer diameter skimmer. Now if you’re talking a TALL 6” skimmer you may want a larger pump that would be powerful enough to battle the head (suction on the venturi side).

I just think that the GenX-1500 is WAY too small for any 6” skimmer of decent height unless it was modified beyond recognition and I can think of better pumps to spend the time with

[ClayWagner]

I like that idea about cutting the floor drain. I been looking around and I really like the plans of the RS-180...It goes for a 8" to 4.5" neck and is only 24" total in height. Plus, I'd be able to put it inline and have it run external. It sells for around 800 bucks! I can get most of the plumbing for free from a friend's father but I need to find a way to go from 8" to 4.5" and make it conical in shape such as the floor drain. So with that and a Sedra 5000/OR equiv/ or Eheim equiv I'd only spend bout a hundred. I just need a nice venturi to go with it. Randy...how hard is it to make one? I like the one you did but don't have all the tools neccessary and it would be worth it just to buy a venturi. Anyway I could buy a nice DIY 3/4" one off ya?

[shelburn61]

Choose the diameter of the neck based on the air flow into the skimmer. I think my link above contains Hahnmeister's formula for determining this... something like ~1LPM/sq. in. tube area

A clear acrylic neck makes tuning the skimmer MUCH easier. 3.5" acrylic tube fits 3" pvc unions and 4.5" tube fits 4" pvc unions.

I've got an extra 4" union if anyone needs it BTW...

[RandyStacyE]

ClayWagner,

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