DIY Venturi, anyone?

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DIY Venturi, anyone?

Postby Studioksr on Sun Mar 27, 2005 9:42 am

I'm going to try making my own venturi for my skimmer -- I've seen some designs on the net, but wondered if anyone here has ever made one.

My skimmer is now working -- since I added an airpump to push more air through the airline (not using a stone in the skimmer) the venturi that came with the pump kept getting clogged (in 12 -2 4 hours), so I quick using that one, and tried a little one from a Rio pump, I think. It doesn't draw enough air on its own, so I am going to try to make a better one . . .

any advice? thanks

- Katherine
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Re: DIY Venturi, anyone?

Postby tapper of spines on Mon Mar 28, 2005 4:53 pm

Studioksr wrote:I'm going to try making my own venturi for my skimmer -- I've seen some designs on the net, but wondered if anyone here has ever made one.


Can you describe what exactly you mean by a venturi? I think I've made what you're talking about, but I'm not entirely sure.

TOS
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Postby Studioksr on Tue Mar 29, 2005 9:39 am

A venturi is a device like a tube that is used on protein skimmers (and lots of other non-aquarium industrial uses) that tapers and narrows a stream of water to increase the pressure past an opening that draws in air as the water rushes past. The tube then tapers and widens back out to flow into the skimmer with a mix of air and water. Airline tubing is attached to the opening, and can be adjusted to vary the amount of air intake.

Some powerheads come with venturis, and there are some that can be purchased separately -- Kent Marine makes a venturi that can be purchased for powerheads. My powerhead (that came with the skimmer) uses metric fittings, so nothing I can buy fits. The powerhead came with an odd little part that drew air in, but would clog almost immediately.

Currently I have my skimmer running using a simple not so effective venturi from another powerhead, which I have supplemented by using an airpump to push more air through. I would like to remove the airpump and use a more effective venturi, and need to custom make it in order to fit my powerhead (the alternative is to replace the powerhead, but I;m not really sure what would make a good replacement. and that's an expensive thing for trial & error)

I have found several DIY venturi plans online, but was curious if anyone here has actually made one.

thanks for asking! Any ideas?
Katherine
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Postby tapper of spines on Tue Mar 29, 2005 10:17 am

Ok, that's what I thought you meant. If you will, allow me to put my physicist hat on.

Studioksr wrote:A venturi is a device like a tube that is used on protein skimmers (and lots of other non-aquarium industrial uses) that tapers and narrows a stream of water to increase the pressure past an opening that draws in air as the water rushes past. The tube then tapers and widens back out to flow into the skimmer with a mix of air and water. Airline tubing is attached to the opening, and can be adjusted to vary the amount of air intake.


What you are describing is a modification of a "Venturi tube," name after Giovanni Battista Venturi who did fluid dynamics research in the late 1700s and early 1800s (because I know you care :wink:). The basic principle is that as the tube is restricted the fluid needs to increase its speed to maintain its flow rate. As its speed increases the pressure of the fluid DECREASES, not increases (since the water is essentially a Bernoulli fluid). This decrease in pressure is what causes the tube to draw air.

I have found several DIY venturi plans online, but was curious if anyone here has actually made one.


I have, except my skimmer sits in my sump, and uses a pump rather than a powerhead to run. To make my venturi, I took a piece of PVC pipe and put it in a pot of boiling water until it softened (not very long). I then took some pliers and squeezed the pipe until it was squished, and held it that way until it hardened. I then took some kitchen scissors and drilled a hole into the squished part of the pipe. I then siliconed a piece of airline tubing into the hole. I then put the piece of pipe on the input of my skimmer pump and Voila! Instant venturi! It works pretty well, though there are probably better designs. I had to go through a few iterations until I had a pipe that had enough squish that it actually drew enough air to work well.

As for modifying this for a powerhead, I'm not sure how to proceed. Can you fit a piece of PVC or CPVC pipe to the input of the powerhead?

HTH
TOS
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Postby Studioksr on Tue Mar 29, 2005 12:44 pm

Thanks TOS -

OOops, I guess my explanation and understanding is off a bit, on the pressure part.

Thanks for explaining how you squished the PVC. That was one method referenced on the net, but without any explanation of how one "squishes" pvc!

That sounds easier than the other methods I found. The one I thought about trying involved using a tapered drill to drill out a chunk of solid acrylic rod. I found the rod, but when I went to buy the drill bit, went into shock at the $50 price tag!

I am waiting for a book I ordered on the engineering of aquarium equipment written by Excobal. Its been on back order but should be here sooon .. . . . meanwhile I am going to try the squishing idea. I didn't realize pvc would soften that much in boiling water.

My skimmer is in a sump also, I get confused between powerheads and pumps -- thought I just read that powerheads are submersible, and pumps are not? doesn't really matter anyway in this case, I think.

- and yes, I love the detailed history of the origins of the venturi :lol: I never had physics -- always on my wish list, maybe when I retire.

thanks very much!

Katherine
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Postby Studioksr on Tue Mar 29, 2005 12:45 pm

sorry about the typo -- author's name is Escobal, not Excobal . . .
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Postby tapper of spines on Tue Mar 29, 2005 12:49 pm

Hey, no worries. Glad to help. :D

Studioksr wrote:My skimmer is in a sump also, I get confused between powerheads and pumps -- thought I just read that powerheads are submersible, and pumps are not? doesn't really matter anyway in this case, I think.


Could be. When I hear "powerhead" I always envision something suction-cupped to the inside of a tank. What pump/powerhead are you using?

TOS
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Postby Carinya on Tue Mar 29, 2005 1:19 pm

I am probably 75% done with a DIY skimmer I found on nano-reef.com. The thread is http://www.nano-reef.com/forums/showthread.php?s=&threadid=30941

It is designed for a smaller tank and is based on the Remora skimmer. UndertheRadar's design was originally for an injection-based skimmer but I think on page 36 or so he realized that a venturi-style one was actually more effective. Body plans remain unchanged as noted on page 13 of the thread but the plumbing changes...I think those new plumbing specs are on page 36, more or less.

Since I haven't completed the thing, can't say if it works. But I am not a very good DIY-er at all and this project so far has come with a minimal amount of frustration. My slow progress is more due to free time constraints.

C
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Postby Studioksr on Wed Mar 30, 2005 10:44 am

An Otto 2100TP came with the skimmer. Its rated at 95 - 539 gph with a max head height of 80 inches. It also has a sliding flow adjustment that controls water intake. It's fittings are metric, but my husband has a mini lathe, and modified a piece of cpvc to fit the pump inlet so I could add an old "mini venturi" part I had around that fits an airline to the pump inlet. That part isnt really a venturi but it does allow air to come in past the impellor and it doesn't clog like the original tiny part that came with the pump.

I asked the skimmer maker what other pumps he would recommend, and he suggested a Rio 1700, but I have tried to avoid Rio's for the past 5 years -- hear bad reports about them back then. I recently did a search on Reef Central, though and several people commented that just due to the sheer numbers of Rio's in use, reports of failures are more common, but not statistically higher than other pumps.

Carinya -- I am impressed that you are building your own skimmer! good luck! I will check out that link later on, to see what kind of venturi is used.
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