Pump Questions for a 6-inch Recirc Skimmer

[pescadero]

Originally posted by pescadero
i also tried air injection. i used an old/noisy Hagen Optima air pump. its rated at 4.2 PSI at its adjustable from 500-5000 cc/min. i had it turned all of the way up, and it did a reasonable job with the quiet one 3000 and the venturi. i was able to get decent aeration of a 5-foot tall water column (about 48 inches of actual head).

so now my questions are focusing on air pump specs. although the Hagen Optima did an okay job last night, i have to admit i was surprised this morning when i found its specs printed on the bottom. based on its performance, i thought that i would need to buy a bigger pump to get the most out of the tall skimmer. i was really surprised to see that it had a PSI rating of 4.2. that equates to 116 inches of water, and the pump doesn't seem to be that strong.

i'm also unsure of what the adjustable 500-5000cc/min flow rates really mean, as i'm sure they're pressure dependent. i haven't found any detailed specs yet.

i'd reallly like to find out more about how this pump is rated so that i can get a better idea how much pump i need to buy for the skimmer.

BTW, do you know the optimal ratio of SCFM per square inch of skimmer neck? i've been looking around but i can't find it. i'm thinking that if i get a big enough air pump, i'll keep the skimmer neck at 6 inches and skip the neck reducer coupling.

[JCTewks]

I believe that 1cc and 1ml are the same....so 5000cc/m = 5lpm or about 11scfh...not a lot of air

The formula for scfH per sq in is 60-70lph per sq in. so....6"neck would be pi X 3"squared = 28.26 sq in of neck area x 70 lph = 1978 lph = 32.97 lpm = about 65-70 scfh. That will handle TONS of air ( i forget from lpm-scfh...but i always figure at around 2scfh/1lpm)

I think you'd be best trying to only put abou50scfh through it so that the turbulebnce from the bubbles is not too high.

[pescadero]

Thanks for the help with the numbers. Here's how I'm looking at it:

Pressure:

I'll have a 5-foot water column. That's 60-inches of water. At the standard temp of 60-deg F, that converts to a static head pressure of 2.16 PSI. So to add some margin for safety, I need a pump that will do at least 3 PSI in order to handle a 5 foot water column.

Flow:

A 6-inch diameter skimmer has a neck area of 26.26 sq. in.
Using your suggested flow rate of 70 lph / sq inch, I'll need 1978 lph. To convert lph to CF/H, multiply by 0.03532 and we get 69.9 CF/H. Call it 70 CFH.

Applying this method to different neck sizes, here are some guidelines for DIY skimmer air flow rates:

NECK DIAMETER--CFM--CFH--LPH--LPM
6--1.16--69.9--1978--33.0
4--0.52--31.0--0879--14.7
3--0.29--17.5--0495--8.24
2--0.13--7.76--0220--3.66

Putting that into perspective, with a neck diameter of 2 inches one would need 7.76 CFH of airflow. My old Hagen pump delivers about 11 CFH of air flow, so it would be good for evaluating a skimmer that had a 2-inch neck on it!

Thinking then about what sort of pump to buy, the first part of the calculations tell me that I need 3 PSI of pressure, and the second part of the calculations tells me that I need 1.16 CFM of air flow.

I've found two Coralife pumps that seem to fit the bill:

SL-38: 1.34 CFM @ 2.9 PSI. $50 at DFS.
SL-65: 2.30 CFM @ 3.9 PSI. $56 at DFS.

Does anyone have experience with these pumps?

[pescadero]

Bump.

i've got a Coralife SuperLuft 65 on the way from DFS. We'll see how it works out...

[JCTewks]

well, it looks like it'll put out about 120scfh....so i think you'll be fine

Remember, you will be pumping into very little pressure when feeding air into the intake...and you won't need a venturi, just a way to get air into the intake side of the pump. On forcefed NW's, the restriction in the venturi is only going to limit the amount of flow/air that the pump can handle....so just get a 1" tee and put an air fitting on the side and let it rip

[pescadero]

Originally posted by JCTewks
well, it looks like it'll put out about 120scfh....so i think you'll be fine

no, i don't think i'll be starved for air! hopefully there will be enough surplus air to allow me to do a few other things besides running the skimmer, like running rotifer & brine shrimp hatcheries.

Originally posted by JCTewks
Remember, you will be pumping into very little pressure when feeding air into the intake...and you won't need a venturi, just a way to get air into the intake side of the pump. On forcefed NW's, the restriction in the venturi is only going to limit the amount of flow/air that the pump can handle....so just get a 1" tee and put an air fitting on the side and let it rip

yes, with forced air induction you don't really need the venturi. but i do think that something that helps to make the air bubbles smaller would be better for the pump, like lots of little orifices rather than one great big one.

being able to get rid of the venturi has now got me thinking about replumbing the system so that i use an internal recirc pump (in the bottom of the skimmer) rather than an external recirc pump. that way i can eliminate two external plumbing adapters, two unions that are potential sources for leaks, and pipes that stick out that could potentially get bumped into and broken off. i could run the airline and the power cord out through the effluent pipe, so that the skimmer would only have one input and one output.

to do that, i'd have to take the threaded inlet plate off of the QO pump and replace it with the flat plate that has a hole in it. that would give me just enough clearance to put the pump in the bottom of a 6-inch pipe. then the question arises of where to drill the fitting for the air inlet. i've thought about tapping a threaded hole for a barbed fitting right into the side of the volute.

[pescadero]

well the pump works great. it produces a huge surplus of air -- so much that i have to bleed it out through a couple of open valves to get the volume of air down to the point that the pump doesn't cavitate. that's with a 5-foot tall water column.

the pump is unmodded. its completely reliable WRT restarts because of the forced air induction. i'm wondering how much an Enkamat mesh mod would help in this situation. i'm thinking that it would help to chop the air into finer bubbles, but that's about all it would do. i don't know whether or not a meshmod would improve the total amount of air that the pump can handle before cavitating.

unlike with an aspiration design, with forced air induction the total air consumption is determined by the air pump, and the only thing that the meshmod would do is to modify bubble size. maybe it would allow better air chopping and allow a higher airflow rate before cavitation, but i'm not sure about that.

the one drawback to this pump is that its so friggin' LOUD! i think i'm gonna have to build a ventilated soundproof box for it or something, as it really needs to sit inside of a muffler.

[pescadero]

oh yes, forgot -- with the airpump turned on, i'm currently getting a rise in the water column hight of about 2.5 inches. that's 2.5 inches of air suspended in the 6-inch column. if i go any higher with the airflow, the pump starts to cavitate.

do you have any idea how 2.5 inches of air suspended in the water column compares to other skimmer designs?

i've got so much surplus air with this pump that now i'm thinking about adding another pump, or stepping up to a tall 8-inch skimmer with multiple pumps.

[pescadero]

more info -- the QO3k is pulling about 25W or a little more when i run it with enough air to make it operate just shy of cavitation. the air pump is also running at about 25W, so the combination of the air and water pumps uses about 50W of power to drive a 5-foot tall reaction chamber. that's better than i was expecting.

[MeuserReef]

Originally posted by pescadero
Bump.

i've got a Coralife SuperLuft 65 on the way from DFS. We'll see how it works out...

pescadero,

Do you think that the SuperLuft 38 model would work for just the skimmer alone without the extra bleeding that you found that you needed to prevent cavitating the pump? I like the idea of not running a venturi.

You have done a very good job documenting your trials and I hope to soon be one of the many to benefit from it!

Thanks

[pescadero]

Originally posted by MeuserReef
pescadero,

Do you think that the SuperLuft 38 model would work for just the skimmer alone without the extra bleeding that you found that you needed to prevent cavitating the pump? I like the idea of not running a venturi.

well, it depends upon the skimmer depth and the flow rate that you're looking for.

to determine how many PSI i needed, i measured the height of the water column that i was going to be using, and converted the height of the water column (in inches) into the equivalent PSI of pressure that the water column created. then i decided that i needed a pump that could supply at least that much pressure to overcome the static head produced by the height of the water column.

for flow rates, that depends upon your skimmer neck diameter. i remember thinking that i could probably get by with a Model 38 on my tall 6-inch skimmer, but i wanted the extra flow available to power other air powered devices. i have to admit that the pump is so doggone loud that i'm rethinking the idea of the tall skimmer, in favor of putting short ones in the tank stands like everyone else is doing. but since all pumps seem to become noisy after a while, it might not be worth worrying about the noise.

all things considered, i don't think that its worth worrying about air injection if you're going to make a short skimmer. asperating venturis work well for that. OTOH, if you want to build something really TALL, air injection is the only way to go.

Originally posted by MeuserReef
You have done a very good job documenting your trials and I hope to soon be one of the many to benefit from it! i'll get around to posting some photos when i'm all done.

Thanks

glad someone's found all the typing to have been worthwhile!

[GuySmilie]

Me too pesc.
I enjoy reading your experimentation results as well.