# Modifying a Powerhead



## hoppycalif (Apr 7, 2005)

At the last meeting of the Sacramento Aquatic Plant Society, we heard a presentation about modifications that can be made to a powerhead, primarily to greatly increase the flow from one. That really intrigued me. The thought that a simple device added to the output of the powerhead could double the water flow opens the possibility of using smaller powerheads and still getting good water circulation. So, I spent the day playing with the idea. (This is not my original idea, by any means. It is a copy of modifications used by reef tank keepers.)

The goal of this modification is to place a "jet pump" or "eductor" on the outlet of the powerhead, so it sucks in the surrounding water to give a lower velocity, but greater volume flow rate. Here is my finished product, not tested yet.

















The "jetpump device" is made of acrylic plastic with a small ring of 1/2" NPT PVC pipe inside to give a small restriction to make it a crude venturi. This is one inch in diameter, and fits on a 1/2" diameter outlet pipe on the powerhead.









To make this also pick up CO2 from the top of my external reactor I added a CO2 tube so it has a tiny exit orifice to feed small bubbles into the powerhead inlet.









Tomorrow I hope to test this.


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## Minsc (May 7, 2006)

Hey Hoppy, can you give a more thorough explanation of how the eductor works?

Some of us need it spelled out a little slower


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## trackhazard (Sep 20, 2006)

Eductor

I've seen a lot of marine applications for eductors although this is the first time I've seen a mini freshwater version. Good job Hoppy.

-Charlie


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## Minsc (May 7, 2006)

Thanks for the link! It begs the question of course, why aren't power heads built like this already

Ah well, some things we will never know. I can't wait to see how this works as a CO2 reactor!


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## hoppycalif (Apr 7, 2005)

Powerheads began as a means of pumping water out of an undergravel filter. So, they had a conical inlet, to fit various sizes of "up tubes", and the outlet was just a simple tube, with various attachments to spread out the flow, suck in air, etc. Most powerheads still have all of those features even though few are used today for that purpose.

Before I accept pats on the back I want to see if this thing actually works. The reef tank guys generally use much bigger powerheads and are trying to get still more flow out of them, so this little weak one isn't what that idea was meant to work on. I'm not yet sure how I will check out how well it works, but I'll try something.

This was my third attempt to make one of these. The first two attempts were with PVC couplings, but those all failed to hold together. It wasn't as easy as I expected, so I gained a lot of respect and admiration for the reef tank folks.


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## hoppycalif (Apr 7, 2005)

I just tested the little dingus. It certainly slows the velocity of the outlet flow, but any increase in volume of water flow is not sufficient enough to be obvious. I set this up in a clear plastic container of water, tried it with and without the device on the outlet pipe. It appears to do much the same thing that the little flapper thingee you get with a powerhead does - it diffuses the outlet flow into a larger diameter. I tried blowing bubbles through a piece of air tubing right behind the half moon shaped openings where the extra flow should be "pumped" - no bubbles were sucked in. If I placed a bubble right at one of the openings it would float in and be ejected, so I assume there is some slight extra flow.

I think any jet of water in a tank of water will pick up extra flow in the boundary between the jet and the still water, so that probably augments the flow about the same amount.

Interesting little experiment, but not productive.

However, another harder to do modification is very likely to work. That is to replace the powerhead rotor with a propeller, so the prop is external to the cavity in the powerhead, and enclosed with little more than a cage so water freely enters the back of the prop. (A cheaper way to get one of these: http://www.marinedepot.com/ps_ViewItem.aspx?idproduct=TZ1313) And, there are lots of how-to-DIY it articles on the internet, on reef forums about doing this.


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## Jareardy (Feb 14, 2008)

thanks for the write up anyways!


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## dansbdk (Mar 16, 2008)

The blades on all the impellers I've seen are short, and flat, with only 4 teeth!
I wonder what would happen if you lengthened the blades on the impeller, or better still, heated, and bent them slightly like an out board motor, or fan blade? 
Seems they would be more powerful in moving the water that way!
Worth a try?


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## hoppycalif (Apr 7, 2005)

dansbdk said:


> The blades on all the impellers I've seen are short, and flat, with only 4 teeth!
> I wonder what would happen if you lengthened the blades on the impeller, or better still, heated, and bent them slightly like an out board motor, or fan blade?
> Seems they would be more powerful in moving the water that way!
> Worth a try?


It could be done, of course. But, the flow rate is pretty well limited by the size and rotating speed of the motor. The really effective modification is to use a higher flow rate powerhead, like a maxijet 1200, and replace the rotor with a model ship propeller. That is what the reef guys developed, for example: http://www.reefchili.com/MJmods.html


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## cholly (Jun 12, 2007)

hoppycalif said:


> The really effective modification is to use a higher flow rate powerhead, like a maxijet 1200, and replace the rotor with a model ship propeller. That is what the reef guys developed, for example: http://www.reefchili.com/MJmods.html


And which principle is the basis for the design of commercially available pumps from Tunze, AquaKorallia and Ecotech's Vor-tech (which I used to use on my last reef). The flow these things put out is incredible, and totally non-laminar. You may find that even a small DIY model puts out too much flow for a small tank; you may have to experiment a bit unless you end up with a commercial model with a variable speed setting.

As a caveat, some of the prop cages used on various commercial and DIY kit models feature pretty large openings. A small fish that makes it past them and into the propellers will be very quickly puree'd.


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## ngb2322 (Apr 9, 2008)

Hoppy

I think this idea would work if the openings near the outlet of the powerhead were a little bigger and positioned differently. I imagine the slots around the outlet looking like the top slot thingy in a recorder (the little flute like thing kids play in music class in elementary school). Sloping in from farther back (maybe a sheath that extends back to the powerhead body) to allow more flow to be sucked in. Maybe I'll try that this weekend and see what I come up with.....


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## hoppycalif (Apr 7, 2005)

ngb2322 said:


> Hoppy
> 
> I think this idea would work if the openings near the outlet of the powerhead were a little bigger and positioned differently. I imagine the slots around the outlet looking like the top slot thingy in a recorder (the little flute like thing kids play in music class in elementary school). Sloping in from farther back (maybe a sheath that extends back to the powerhead body) to allow more flow to be sucked in. Maybe I'll try that this weekend and see what I come up with.....


Please do try it, and let us know how it worked, plus how you made the device.


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## pinantanjohn (Apr 20, 2008)

I believe what the concept here is a venturi. You pass the the pressurized stream past the end of another feed pipe and the stream drags extra water from the feed pipe. What has to be calculated (experimented) is the ratio between the "pump stream" volume, the "extra feed" volume and the outlet volume. The basic idea is to create a slight vacuum right where the end of the stream pipe connects with the outlet. I should think that a basic ratio should be a good starting point. Something like if you have x in^2 of stream cross section and say x/2 in^2 of feed cross section then the outlet pipe should be just a little bit larger than the sum (1-1/2x + 1/10x (or something like that)) of both the feed and stream. Not too much though, or you will create a load on the pump because of the flow restriction of the feed pipe. The length of the overlap has some effect as well. It needs to be a minimum length (probably a ratio of it's diameter, try 5:1). Anything over that shouldn't make a lot of difference but too short really will make a difference. I would think that chamfering the inside end of the stream pipe where it intersects with the mixer to reduce turbulence and the inlet end of the extra feed pipe to facilitate smooth flow will help and reduce drag on the system. Confused? I was. It took a lot of little drawings to get that straight. Testing needs to be done without back-pressure or it won't work.

Here's a graphic of the concept
It's not to scale or even designed for anything other than the concept. It's going to take some experimentation to get it right.
For CO2 injection, I would suggest another small pipe inside the flow pipe so that the flow draws the gas out just like the venturi in a carburetor on a car. Same concept except that CO2 has a much lower viscosity than water so the difference needs to be greater (smaller gas pipe, larger flow pipe (wider ratio?).
Hope that helps...

Peace...
John
(sorry 'bout the crappy image, can't get detail with the file size limits)


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## hoppycalif (Apr 7, 2005)

John, I agree with the concept you described. The best example we have is the Python jet pump that works much the same way. Cutting one of those in half to see the configuration might be educational.


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## Sparg93 (Mar 31, 2008)

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