DIY Group Project - Eductors

[thebutler4]

Thats very cool! ... I bet they would work better if the barbs where sanded off though less resistence ... what do you think? ...

[Weatherman]

The smoother and more aerodynamic the intake the better.

You want water to easily accelerate into the mixing tube from that side. Otherwise, the pressure drop from the eductor nozzle will cause water to be drawn in from the opposite side of the eductor where water is trying to exit.

[Geoff]

Vince, those are great renderings!!!

absolutely smoothing off the barbs will help a lot.

G~

[Tim224DT]

Looks like it will be a good first group project............I have no use for one right now so i am waiting for the next DIY project.

But Geoff you will keep these in an archive somewhre right?

Tim

[Geoff]

Originally Posted by Weatherman

Here’s my reasoning for the use of eductors:

I want 3000 gph flow in my tank, to keep my coral happy, but I only want 700 gph flow through my sump to cut down on microbubbles.

How do I do that with one pump?

I could compromise, and get a pump that runs around 1500 gph, but then I’d have too little flow for the main tank and too much flow for the sump.

So, what do I do?

I get a pressure-rated pump, capable of running about 1000 gph at 4’ head, and put eductors on the return lines. The nozzles on the eductors will throttle the flow through the pump (and sump) to about 700 gph, and the mixer and diffuser on the eductor will enhance the flow out of the eductor cone by about 4-5 times the flow through the eductor nozzle (2800-3500 gph).

The result is the best of both worlds, all through the magic of the remote conversion of potential (pressure) into kinetic (flow) energy.

i agree with your reason for the eductor, but i think you math is a bit off.

i have found that an eductor will add at least 7-10 feed of head pressure to the pump. in your example that would mean you would need a pump that could pump pump at least 700gph at 11-14' minimum. the 7-10' of head pressure plus the head height of the return.

you can quickly see how pressure pumps really show thier own when it comes to eductors.

a good example of a good eductor pump is the Blueline Velocity T3. it can handle 28' of head pressure. it has a very steep pump curve so it holds most of the 850gph all the way up to 20'. using the example above at 14' of head pressure the pump is pushing 540gph. multiply that by 4 you get 2160gph of total flow out of a pump only rated for 850gph!!! to boot it only uses 140w of power!!

G~

[Weatherman]

Originally Posted by Geoff

i agree with your reason for the eductor, but i think you math is a bit off.

That's true, but I was just taking a guess at the numbers.

Let's get more specific.

Based on this reference:

http://www.marinedepot.com/aquarium_...nformation.asp


An Iwaki 55RLT looks like it pumps about 17.5 gpm (or 1050 gph at 4'). The pump is quoted as running 1080 gph at 4', so the estimate off the graph looks close.

Let's go up to 14'. Looks like around 12.8 gpm (768 gph). So, the Iwaki 55RLT is doing better than the 700 gph I guessed before. Assuming a 4-5 times enhancement of flow from the eductor, you get around 3450 gph.

An Iwaki 55RLT uses 1.6 amps. Assuming 115 volts, you get a power draw of 184 watts.

[Geoff]

Originally Posted by Weatherman

That's true, but I was just taking a guess at the numbers.

Let's get more specific.

ohh, fine, pick the one other pump that could fit your calculations.

i should have asked which pump first. i was guessing that you were thinking of the ubiquitous Mag 12.

G~

[Weatherman]

A good rule-of-thumb, when it comes to choosing an appropriate eductor pump, is to check the flow at 4’ head and the flow at 14’ head.

If the flow at 14’ is less than one quarter the flow at 4’ you might as well not bother trying to run an eductor off that pump.

I just wish more pump manufacturers would publish the flow curves for their pumps.

[Viv]

I have a little giant, at 3ft -1225, 6ft.-1080, 12ft.-drops to 675 with max head at 17.0ft. I figure I'm borderline, but should get some increase in flow out the nozzle. What will be even better is to widen the flow out the nozzle as currently the stream is very hard and coarse...the eductor should help with this correct?

[tims]

Why sand the barbs off? will they really restrict the flow?
How does it stay on the line?..
i will go shopping this weekend?

[Geoff]

the barb tips create little eddies on their leading edges which disrupt the inflow of the external water towards the higher pressure nozzle. this just makes it less efficient. sanding them down smooth will give the incoming water a nice transition to being sucked along with the released water from the high pressure nozzle.

G~

[Geoff]

Originally Posted by Viv

I have a little giant, at 3ft -1225, 6ft.-1080, 12ft.-drops to 675 with max head at 17.0ft. I figure I'm borderline, but should get some increase in flow out the nozzle. What will be even better is to widen the flow out the nozzle as currently the stream is very hard and coarse...the eductor should help with this correct?

yes it should help in widening the exit cone of the flow. with that amount of flow i would prolly try the 3/8" nozzle. this nozzle seems to work best in most cases. the lower the pressure rating on the pump the bigger the nozzle should be. also the shorter the nozzle should be.

G~

[Viv]

shorter the barb or shorter the nozzle? I thought the larger the holes or openings to let water in would increase the amount exiting, and the longer the nozzle the better the mix or flow. ie. why not put on a long piece of pvc for the nozzle wouldn't it all more water to be pulled into the eductor?

[VWD]

Nice Vince. That really shows it going togather.

[Geoff]

Originally Posted by Viv

shorter the barb or shorter the nozzle? I thought the larger the holes or openings to let water in would increase the amount exiting, and the longer the nozzle the better the mix or flow. ie. why not put on a long piece of pvc for the nozzle wouldn't it all more water to be pulled into the eductor?

you are correct on all counts.

should have been clearer. shorten the barb.

how long do you want the eductor.

as the eductor nozzle gets longer it has to flair out more and more. if not than it will create back pressure in the eductor nozzle and limit the amount of water that can be pulled into the nozzle.

G~