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gman0526
10-19-2005, 07:51 PM
Can anybody see a problem with using an 3/4" eductor on the output of a Mag 12 with about 3ft head and 1-90 degs. elbow and 2-45 degs. elbows? Thanks for your input.

jlehigh
10-19-2005, 07:56 PM
From my research (not experience) The Mag12 does not produce enough preassure to effeciently/effectively operate an eductor. Mag pumps are flow pumps great for moving allot of water under little to no head-preassure.

Eductors are recommended be used on pumps rated to at least 10psi. Operating from memory I believe that is about 23 head ft. As I recall not even the mag18 can push a single eductor..

You will be best off purchasing a preassure rated pump rated to at least 10psi. Several of our sponsors carry Blue-line and Iwaki pumps which are preassure rated..

wrightme43
10-19-2005, 10:02 PM
Now this is from experince. LOL and many I have that just because I am hard headed. LOL
I have a eductor on a quiet one 6000 pump to a 1" seaswirl. It works just fine. I know it does not operate to its maximum potential. It does cause a massive increase in the amount of flow in the tank. I have a tunze 6100 and the 1" seaswirl w/ eductor. Its in a 75 gallon tank so it is more than enough flow. I figure it at more than 50x tank volume turnover per hour.
I figure I am getting 800 gph at the seaswirl from 1506 at zero head. I figure the eductor doubles it to 1600 plus the tunze does 3100 a hour and is at max power 1/2 of the time and half power one half of the time. So that is about 2300 gph average. So if I am right and I could very well be wrong I have 3900 gph in a 75 gallon tank.
Steve

dnjan
10-20-2005, 11:06 AM
Be careful Steve - you aren't creating mass or anything there, are you? Wouldn't want to sick the physics police on you :)

What an eductor does is to use a high-velocity, small-diameter water stream to draw in more water, and convert the combination into a larger diameter, lower velocity flow. Actual, total flow (gallons per hour moving past a specific point) is not increased. Rather, the width of the stream is increased while the flow velocity is slowed down. Since it is hard to see the decrease in velocity of the water molecules, what most people see is that a wider area (cross-section) of water is moving. Or, if you held your hand in the tank on the opposite end from a pump outlet, without the eductor you would feel the flow on a small part of your hand but with the eductor it would feel like your whole hand was being pushed by moving water.

The same thing could be accomplished by a properly-tapered outlet nozzle. The problem with that is that the nozzle would need to be quite long. An eductor allows this conversion to occur in a fairly efficient manner over a much shorter distance.

Note - any eductor will have a small head-loss associated with it. Meaning that the total flow is actually reduced a bit by using an eductor. However, the eductor's ability to convert small-diameter, large velocity into large-diameter, lower velocity (which is more useful in our tanks) at a relatively low cost in terms of head loss makes them attractive for some applications.

gman0526
10-20-2005, 08:10 PM
Note - any eductor will have a small head-loss associated with it. Meaning that the total flow is actually reduced a bit by using an eductor. However, the eductor's ability to convert small-diameter, large velocity into large-diameter, lower velocity (which is more useful in our tanks) at a relatively low cost in terms of head loss makes them attractive for some applications.

That's exactly what I'm looking at, i know as wrightme43 that i surely won't get the 5x's optimal flow that the eductor is capable of producing but I'm thinking that maybe a 2-2.5 times would be great. Correct me if I'm wrong but this is basically the same principle as a let's say, Calfo manifold. In a manifold you would use for example a 1" PVC to build the main frame of the CL and use a smaller diameter T on the outlets to increase velocity. Only difference as far as the outlets is concerned is that in the CL theres no holes so more water can be drawn in to increase flow amout.

Anyways, TY very much guys for your insight/experiences.

wrightme43
10-21-2005, 12:08 AM
We used a eductor on the submarine to drain the sonar dome. Hook up a fire hose and the water flowing thru the fire hose to the eductor would also pull water along and out of the sonar dome out into the bay. It had to actually increase the amount of water flowing or it would of never emptied the sonar dome, which I might add is a freaking sucky place to spend 4 weeks in the middle of july taking every single stinking nut off of every single stinking threaded stud on every single stinking transducer because the shipyard used the wrong type of nut and they were rusting away. Then rethreading every single stinking stud and then torquing every single stupid nut.
I am going to go and do some research and make sure I am right. I know they had a big foo fa rah on RC about this whole deal. I got tired of reading one dudes "Just stack them end on end and fly to the moon on one rocket" deal over and over so I left.

dnjan
10-21-2005, 08:47 PM
Sorry - my mistake. I was conserving momentum, and I should have been conserving energy. Since an eductor slows down the velocity, there will be an overall increase in flow. With energy equal to one half mass times velocity-squared, a decrease in velocity of 25% will lead to an increase in the volume of water moved (ignoring frictional losses) of a bit over 75%. Even with frictional losses included, there will be a significant increase in total flow, as long as there is sufficient velocity in the first place.