# Benchtop Test Tank

test tank

143 replies to this topic

### #41 atlasstone

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Posted 21 February 2013 - 08:44 AM

...You could measure water speed by filming a small object traveling with the water through the test section.  Something light like a piece of feather would be good, preferable have it suspend in the water rather than float on the surface or sink to the bottom.  A couple of strips of tape can mark the distance and frame count will give you accurate enough time.

Get out of my head man!

I did exactly that last night and would have had this posted but decided to go to bed while YouTube processed the video.  Anyway...
I made 4 runs, each with the center section in slightly different places to test the difference in the current.  Some of the flows are not optimal to run a lure in, but the point was to test the speed.  The video was shot and edited at 60 frames per second but if you don't trust my math on the video and decide to do it yourself, then you will need to use 30 frames per second because YouTube renders all their videos to 30 frames per second (at least that is what I understand... I would need to confirm that though)

The tape is approx. 3/4" and I counted frames across a 6" span.  I hope this hepls!

http://youtu.be/QqBp7e7h9Hg

Edited by atlasstone, 21 February 2013 - 08:47 AM.

### #42 JBlaze

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Posted 21 February 2013 - 10:10 AM

I've considered building some sort of test tank for a while so have "run the numbers" on a few configurations.  Thinking about this one (today) I realized you may be getting some retained momentum because of the recirculation (like some wind tunnels) so velocity may be quite a bit higher than the .5 ft per second you'd get from pump output alone in a straight-through configuration.  You could measure water speed by filming a small object traveling with the water through the test section.  Something light like a piece of feather would be good, preferable have it suspend in the water rather than float on the surface or sink to the bottom.  A couple of strips of tape can mark the distance and frame count will give you accurate enough time.

This is my thoughts are taking me.  I started putting it together last night will hopefully have something to show in a couple of days. I thought maybe a suspending lure might do the trick as far as measureing the speed/flow. Thanks for the reinforcement

### #43 atlasstone

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Posted 21 February 2013 - 01:38 PM

JBlaze,

I tried a lure but without a tension point it doesn't have the control needed to measure it.  I used a disk made from PVC with a little bit of weight in the center to keep it running as straight as possible.  I didn't think about it until you mentioned the suspending lure, but you could use the same concept with the disk maybe and just add enough weight to give it neutral bouancy.  I still have mine set up so if it would help, I can mess with it and see what happens.

### #44 JBlaze

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Posted 21 February 2013 - 02:35 PM

Atlasstone, I think that is a good idea, worth trying.

I have another idea also, I'm not sure this would work but maybe drop in a small hose from an aquarium air pump and blow a single bubble and see how far it traveled before surfacing. No weight or mass to affect its momentum so it would instantly travel at the speed of the flowing water. I think  Geez, I can't sleep at night for thinking about this thing.

### #45 atlasstone

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Posted 21 February 2013 - 06:46 PM

I'll give it a shot and see what happens.  I'm sure others that are more physics savy can confirm this, but I don't think the object itself really matters.

For the purpose of testing, I chose a round shape so that the distance traveled would be as accurate as posiible regardless of if it spun.  If it were a rectangle and the object spun 90 degrees in the middle of the measurement, it would throw the calculations off because I would need to compensate for the added length at the end... and I'm just too lazy and not that smart.

If the object is unhindered from moving in anyway, then I think any object that is suspended in, or floating on the water column would move the same speed as the current. Much like a boat with a drift sock. If there is no wind to move the boat faster than the current, then the drift sock is useless because it will move at the same rate as the boat which is identical to the speed of the current. Only when another force acts against it will there be a change.

Here is a link that explains it a little better:

I think the question I need to answer by suspending the object is whether the current under the surface is the same speed as the current at the surface.

Am I off base on this?

### #46 JBlaze

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Posted 21 February 2013 - 07:44 PM

Atlasstone, I think you are spot on. But, I am not a physics major neither.

A couple of days ago, after reading and trying to understand the things I read about Laminar Flow. I decided that my end pieces with matching holes drilled was no good.

I liked the idea of building a baffle out of straws but if I figured right, it was going to take close to 8000 cut straws placed in a frame side by side and top to bottom with each straw glued together. Dont think I have that much time or patience.

So instead I am opting to build a baffle for each end made of stacked and glued strips of corrugated plastic sign material. The plastic is very thin and strong and should have several thousand small holes/channels for the water to flow through. I am thinking that the secret to a good strong flow will be to have the pump pumping the maximum amount of water that this baffle will allow to flow through all those holes. If it pumps more than the baffle will handle then the space between the baffle and the end of the aquarium will overflow. On the opposite end, The same thing should occur since the baffles will be identical and the return  inlet of the pump should be pulling from behind this baffle the same amount of water it is pumping out to the other end. This may take two or three pumps. I have no idea how to figure how many gallons of water can flow through this thing.

My biggest worry with using the corrugated material is that the channels are so small that there may be too much friction and the water may not flow well.

Ain't but one way that I know to find out  if it will work or not so with that said. I am going to be busy for a few days.

### #47 atlasstone

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Posted 21 February 2013 - 07:53 PM

Would your design allow you to scale down at all? Perhaps only fill 1/4 of the tank and see what happens.  You could bujild a frame to hold the straws and run the pump slow enough that you can just use friction to hold the straws in.  Just trying to save you a little time and energy

Did the video with the speed tests help at all?  I'm not sure what posts are getting through because I seem to have posts disappear and re=appear.

### #48 Anglinarcher

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Posted 21 February 2013 - 11:38 PM

............... Thinking about this one (today) I realized you may be getting some retained momentum because of the recirculation (like some wind tunnels) so velocity may be quite a bit higher than the .5 ft per second you'd get from pump output alone in a straight-through configuration...............

The video indicates that you may be dead on.  Either that or the pump is pumping more then it claims.

This has been bothering me some just like others on this site.  Most pumps are rated with some "head".  For example, it will pump x gpm at y feet of head.  A bildge pump does not have that rating, nevertheless, I assume it is normal to assume it is pumping that at about 5' of head to get it over the top of the boat.  With no "head" or vertical lift, you could be getting much more then the 1200 +/- GPM claimed.  Hmmmmmm

### #49 Anglinarcher

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Posted 21 February 2013 - 11:48 PM

Atlasstone said:

"I think the question I need to answer by suspending the object is whether the current under the surface is the same speed as the current at the surface.

Am I off base on this?"

No, you are not off base at all.  In water flow systems design, we often use a trapazoid shape so that the water on top flows closer to the flow rate at the bottom.  If you do any stream fishing with "floats" and weighted flies/lures/baits, you will often see the float tip forward because the slow flow at the bottom holds it back some.

The real question is "is there enough of a difference in the 4 or so inches of the tank to matter?".  I kind of doubt it, but then again, I doubted the velocities that you clearly have proven with the latest video.  Only testing would prove one way or another.

### #50 wchilton

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Posted 22 February 2013 - 02:28 AM

I am opting to build a baffle for each end made of stacked and glued strips of corrugated plastic sign material. The plastic is very thin and strong and should have several thousand small holes/channels for the water to flow through...My biggest worry with using the corrugated material is that the channels are so small that there may be too much friction and the water may not flow well.

Friction slowing things down would be my concern as well.  If you already have the material and don't mind spending the time it's worth a shot, though.  I think it might be possible to make a laminar flow nozzle a lot smaller than the whole channel size.  Part of what got me interested in this post was I recently saw a DIY project to make a laminar flow fountain and was considering whether what I had gleaned from that could be used for lure testing.  Just do a google search on "laminar flow fountain" and you'll get lots of hits.  The project I was looking at was at makezine.com.  So my thinking was to either put a laminarizing nozzle on the pump to create laminar flow before entering the main stream of water or to fabricate a small jet pump (powered by the sump pump) to pull water from the main channel and force it all through a larger laminarizing nozzle followed by smooth expansion back to the main channel.  The trick, of course, is going to be minimizing friction loss so that you only need the small pump.

### #51 hazmail

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Posted 22 February 2013 - 04:35 AM

Frustrating isn't it--been here done some of it --for what it's worth here are some alternatives,  although I still feel the prop is the way to go.

Instead of drinking straws (for reducing turbulance) maybe use short lengths of 1" PVC pipe stacked OR irrigation hose which is very thin walled, just glue them togeather  - OOOOOOOOOr maybe ice cube trays.

The retired fireman in me says look up 'Relay Pumping'-- this is a poor man's three stage pump:

Run the outlet from the first pump into the eye of the second pump which in theory will double the flow, then into a third pump and it will double again

( 1200 ---> 2400-----> 4800 GPH) -Keeping in mind you will need to increase the outlet line of the second and third pump to allow for the extra flow into the next, otherwise I think you will only get an increase in water pressure.

For a rough 'speed indicator', buy a cheap digital bicycle speedo (with the magnetic wheel pickup-- pinch one off your kids bike), find a small wheel and calibrate the speedo to the wheel diameter, add some paddles to the wheel (OR very small model boat prop is what I used @ about 1" dia) and away you go. I made one of these for my boat years back and once 'calibrated' properly they are pretty accurate.

Even if this is not accurate enough, any increases you get will be realtive to your initial reading.

Hope this helps and doesn't throw you off track    .

Pete

Edited by hazmail, 22 February 2013 - 04:36 AM.

### #52 Vodkaman

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Posted 22 February 2013 - 05:27 AM

Great thread and great progress made. So glad the Wchilton was right and there was more to it than just the pump rate.

Have you tried a lure in there yet, to see if you are reaching the minimum flow to start the lure action?

Keep up the good work

Dave

### #53 JBlaze

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Posted 22 February 2013 - 08:57 AM

Friction slowing things down would be my concern as well.  If you already have the material and don't mind spending the time it's worth a shot,

With no "head" or vertical lift, you could be getting much more then the 1200 +/- GPM claimed.

wchilton, I do already have the material. So I am going to give it a shot.

Also, I think you are right about the increasing velocity/pump capacity effect caused by the no head and the retained momentum of the recirculating water.

This thread is getting more and more interesting. Thanks everyone for all the input and a very big Thank You to Atlasstone for starting it.

John

### #54 Travis

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Posted 23 February 2013 - 02:14 PM

I'll give it a shot and see what happens.  I'm sure others that are more physics savy can confirm this, but I don't think the object itself really matters.

For the purpose of testing, I chose a round shape so that the distance traveled would be as accurate as posiible regardless of if it spun.  If it were a rectangle and the object spun 90 degrees in the middle of the measurement, it would throw the calculations off because I would need to compensate for the added length at the end... and I'm just too lazy and not that smart.

If the object is unhindered from moving in anyway, then I think any object that is suspended in, or floating on the water column would move the same speed as the current. Much like a boat with a drift sock. If there is no wind to move the boat faster than the current, then the drift sock is useless because it will move at the same rate as the boat which is identical to the speed of the current. Only when another force acts against it will there be a change.

Here is a link that explains it a little better:

I think the question I need to answer by suspending the object is whether the current under the surface is the same speed as the current at the surface.

Am I off base on this?

Might want to take a look at an orange for testing.

### #55 JBlaze

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Posted 25 February 2013 - 09:02 PM

Am off to a start on the test tank. Still need to make and install the end baffles.

http://s253.beta.pho...html?sort=3&o=0

### #56 atlasstone

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Posted 26 February 2013 - 12:49 AM

Have you tried a lure in there yet, to see if you are reaching the minimum flow to start the lure action?

I have on mine.  There is a video link on the first post.  I neglected to embed it so it's kind of hidden.  The action will start at fairly low speeds but I really wanted to test my lures to see if they 'lay down' when cranked fast so that was the point of the exercise for me.

Thanks everyone for all the input and a very big Thank You to Atlasstone for starting it.

No problem!  I'm glad to see it taking off and other design ideas floating around.  It looks like you have a really clean design going so far JBlaze.  I'm anxious to see how it progresses.

Does anyone have any thoughts on whether or not an anemometer would work for speed testing?  I suppose if it's all relative, then it would be a cheap and consistent device for use to comapre speeds with.

### #57 Vodkaman

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Posted 26 February 2013 - 06:17 AM

Atlasstone - Yes, I saw that vid - very impressive result.

Dave

### #58 JBlaze

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Posted 03 March 2013 - 08:09 PM

Up date on the Test Tank.

This is what I am using to make my Baffles

This baffle is almost finished and ready to install. There are ninty-five of the 3/4 inch strips in it for a total of 4750 channels/holes for the water to flow through. I have to make another one for the other end. I hope to finish this thing this week and find out if this was a good idea or not. What do you fellows think. Will it have enough flow to be able to test lures.

I some how deleted the pic of the tank in the other post, Here it is again.

Edited by JBlaze, 03 March 2013 - 08:13 PM.

### #59 Vodkaman

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Posted 03 March 2013 - 11:41 PM

JB - try it with just one baffle first, may not need the second.

Dave

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