Needlewheel to Meshwheel skimmer mod

[Delphinus]

I modified my ASM G3 (Sedra 5000 pump) to a meshwheel skimmer this weekend. Here's what I did:

1) Cut off all "needles" from the impeller except for 4, 1 each at the "12:00", "3:00", "6:00", and "9:00" positions. (My thinking is that this will help prevent "slippage" of the mesh as the impeller turns.)

2) Cut a 3 squares of Enkamat PF4 mesh material, large enough to cover the impeller wheel. Each is 1 layer.

3) Trim the mesh down to the impeller wheel.

4) Weave some fishing line into the mesh to attach. (Some people use zip ties, I thought this might work a little better).

The impeller did not immediately want to start turning, which makes me think I may not have trimmed it back enough. However with some fiddling I was able to get the impeller to turn when the pump is powered on, so I left it. I wonder if 2 layers may have been better than 3 for this reason (well that and one other reason, more on that below the pictures).












I can safely say that this mod does make the skimmer produce more foam, so I am pleased with the modification (and relieved that I didn't wreck an impeller for nothing - as replacements cost around $50). In 24 hours my skimmer has produced a full-on inch of skimmate, which is hands-down the best it's ever performed.

However, I did some before and after airflow measurements with a 0 to 25 lpm range airflow meter from Muis Controls, and the #'s don't show a difference. Before with the "stock" impeller I read about 5 lpm nominal (with spikes to 10 lpm), which is exactly the same readings as with the modified impeller. So I'm somewhat at a loss to explain why people on RC claim improvements from 5 to 12-18 lpm, however I suppose there are many factors/variables at play, such as venturi design, pump model, how the pump is plumbed, etc. Based solely on the visuals and not the measured airflow numbers, I know the skimmer is producing more foam than before, so I'm pleased with the mod.

However, I am left wondering if this may also be an argument to trying 2 layers over 3, perhaps the mesh density is a little too high to prevent an "even better" air suction.

Over time I may experiment with other air injection methods to see if I can improve on the air flow #'s, but for now I'll leave that as a project for another day.

[SuperFudge]

Very nice work tony,


I think the real difference, and the reason for the more air claimed on the other threads... is now you should be able to inject the air you need without it cavitating prematurely, on its own i would have even expected a small drop in pull on air.

Now youll get a finer bubble, and more air.

Did you hone out the volute at all ? ( caution again...several people have gone through the housing.)
Doing this should also enable more air to be accepted without burping, while allowing more room for mesh to spin freely.

Is this a recirc version ?

Good job !

[kwirky]

egh, nice to see you had the guts to chop up your impeller without having a spare around

[EmilyB]

Originally Posted by kwirky

egh, nice to see you had the guts to chop up your impeller without having a spare around

No kidding, I'm hoarding my extra impellers from those bad pumps now....big money $$$

[christyf5]

Wow Tony, you finally took the plunge! Thank God it worked eh?

One thing I noticed after doing the mod myself (without cutting the needles off the needlewheel cuz I'm a big chicken) was that if you don't have the enkamat trimmed back pretty well on the needlewheel the pump won't start up right away. Even after some generous trimming I find it takes a few seconds for the needlewheel to kick in. The bubbles are definitely finer and the skimmer produces more skimmate than before

This has given me more courage to cut the needles off but I'll still procrastinate some more till I do it

[Delphinus]

It took me a full on month after getting the enkamat to work up the courage to start cutting the impeller. Even after reading thread after thread, page after page of it on RC and other boards, I was still hesitant (because I find I always tend to be the one exception where things don't work as well as they do for others). I even ended up pulling the sump and reworking the baffles in an effort to procrastinate on the impeller mod. I finally convinced myself by making sure I could order a new impeller.

Marc, no I didn't grind out the volute. I totally envision myself screwing that part up .. I'll have to do some reading and see some pictures of it being done before I'll get the nerve to try that. I can sort of see it being helpful, but I totally see me just finding out in the end that I just wrecked the pump.

Wait .. is the volute the cap that goes over the impeller or is it the part where the impeller sits in the pump itself? It occurs to me that I'm not even sure what a volute is.

And I didn't realize that people were pushing air into the skimmers. So is that a more common thing then? You were the first person I ever heard of who was directly pushing air in, but I thought it was because the skimmer and the pumps you're using are .. um .. well .. somewhat larger than average?

Would any old airpump do? I suppose I could try experimenting with different pumps I've got lying around. I spent the money on the flow meter might as well try to get some use out of it. If I find anything out about how much air I can push, I will post some results in here.

[kwirky]

i remember when reading about building air driven skimmers you have to use non-diaphram air pumps. dunno if it'd be the same case for a force air venturi skimmer

[Delphinus]

The problem there is that the backpressure of pushing air through the wooden airstones is hard on the diaphrams and they stretch out and lose their effectiveness after a while. In this case you'd be pushing air into suction anyhow so it should be OK. Having said that though, I don't know what a typical air pump pushes in terms of litres per minute. It could be that you still need a spendy-ish air pump just to get the requisite volume of air moving into the skimmer. I don't know, but I can assure you I'm wasting my time here at work looking into this very thing as we speak

[Joe Reefer]

Tony if you dont mind me asking, How much did the airflow meter cost?

[Jaws]

I'm getting pretty close to doing this mod too so I'm just tagging along to hear everyone's experieces.

Can you use a dremel to cut the needles off or do you think a knife or blade is better?

Where's the best place to order a Sedra 5000 impeller just in case?