Preasure pump required for eductor?

[fredfish]

Subject says it all. I am currently running a quiet one as a return pump. Can I use an eductor on the return or do I not have enough presure? I couldn't find any pump spect for the quiet one.

Fred.

[fredfish]

Anyone???

[Geoff]

i was actually trying to hunt down information on the pump for, since i do not have any direct experience with this pump. i am looking at the aquatic eco-system catalog for both the pump and an eductor. and a feet to psi chart. what i come up with is, does not look good, unless your eductor is smaller than a 3/8" eductor. aquatics has a 3/8" eductor that needs 7.5-17 gpm or 450-1020gph at, now this is the kicker, 10-50psi. the quiet one pump can do 1100 gph at 0 so the amount of flow is not a problem. 10 psi equals 23' of pump height. according to the quiet one chart, the pump effectively stops pumping at 12' of head. so according to all of these charts it does not look like it would work. this is all according to "a book", since i do not have any experience with these pumps or eductors in general, besides curiosity. i was hoping somebody else was going to chime in with real answers, but since i was also thinking about doing this, i would go ahead and answer it with what i have found.

Welcome to the TRT!! sorry for the slow start, but that is pretty good specific question, but i was a little surprised that the other DIY guys did not jump in before me.

G~

[Minnreefer]

I was coming across the same problem. I am trying to find a pump that would work well with the eductor also. I believe that the only internal pump is the dolphin ump that is sold at www.marinedepot.com other wise Iwaski pumps would work, I think the smallest is an Iwaki 30, you can find the link here http://www.kthsales.com/website/Misc...r_enthusia.htm

Welcome to TheReefTank

Jon

[fredfish]

Thanks guys. I figured it would not work, but it can't hurt to ask.

Thanks for the welcome.

Fred.

P.S. I wonder if a powerhead creates enough velocity for an eductor type device to work? I suppose even if you only get a doubling of volume, it would still be worth it.

[Geoff]

Originally posted by fredfish
P.S. I wonder if a powerhead creates enough velocity for an eductor type device to work? I suppose even if you only get a doubling of volume, it would still be worth it.

i am pretty sure it is not the velocity that is the problem, it is the pressure requirements. i would be very surprised if any PH could power an eductor. without a sealed impeller assembly a pump can not handle any real back pressure.

i do not know what actually occurs if you run an eductor at below pressure, this is the part i have no clue on. i have no idea if it will actually increase the flow at all or just make it a really big directional nozzle.

G~

[Minnreefer]

I hoked up my 3/4 directly to a mag 12 and did not notice any improvement, actually a decrease. A power head might make it work somewhat but I don't think that it would be enough.

HTH

P.S. I understand, I got one hoping that it would work on my system, but it does not seam to be doing the job. I may get the dolphin pump for a return pump.

[fredfish]

I guess I don't really understand the science of how an eductor works. I would have thought that pressure translates to increased velocity as the water exits the nozzle.

Oh well...

Fred.

[Geoff]

Originally posted by Geoff
i am pretty sure it is not the velocity that is the problem, it is the pressure requirements.

i actually said the wrong thing. it is not the amount of flow that is the problem with most pumps, but the velocity of the water that the pumps can produce. increasing the pressure will increase the velocity of the water, but will lower the volume of water. the volume of water that does not make it through the nozzle becomes back pressure to the pump. eventually the pump will reach an equilibrium. what usually occurs is the back pressure becomes to great for the the pump to push all of the water through the pump outlet, and the rest is spilled out around the impeller. this is why i would really doubt any powerhead could run an eductor. PH do not have sealed casings around thier impellers, so the water has an easy way out when the pressure get to high. it takes a big pump to produce those pressures. i am not including diaphram pumps in this discussion, but that is a different beast.

HTH, sorry for the confusion,

G~

[fredfish]

No problem. So what you are saying is that pressure pumps create a much higher velocity of water at the nozzle than non-pressure pumps. Even a quiet one at 0' head would produce insuficient velocity?

Fred.

[Geoff]

this is where it gets confusing. flow and velocity are different. at 0 psi the quiet one produces 1100 gph of flow. so at 0 psi the pump can produce enough flow for the eductor, but the velocity is not high enough. all of my calculations are based on this one 3/8" eductor. but we are going to assume 10psi is needed to get the velocity throught the nozzle necessary for the eductor to work. for every 1 foot of depth in sea water psi increases .445 PSI. this also equates to head height for a pump. in order to get up to 10psi then the pump would need to handle a head height of 22.47 feet! wowsers. if you look at the chart above for the quiet one it can only handle a head hight of 12 feet or 5.34 psi. this is why those big pumps are the only ones that can handle eductors. i am either right on or way off on these calculations. but all the info. i have been finding on eductors points to these calculations as correct.

G~

[fredfish]

Think I got it this time. With a pressure pump as the pressure increases, velocity at the nozzle goes up. With a non-pressure pump as the pressure increases, output drops so you don't get much of an increase of velocity at the nozzle.

Thanks.
Fred

[Geoff]

like i said all of the calculations and assumptions were based on the eductors i found a aquatic-ecosystems. i have no-idea of these are efficient or inefficient eductors. there may be smaller ones out there that can work at lower pressures. i just hope i gave you enough information to see if other eductors could work with that pump.

thanks for helping me think through all of this,

G~

[jjkahler]

Hi, new to the board and have been following the eductor series of threads. This might sound dumb, but just curious as to what pressure/velocity differences would occur if a pump was pumping down (neg head pressure) instead of pumping up (positive head pressure) as we all seem to do now? I know that there would probably be several problems with this, such as cavitation, siphoning, etc. Just curious as it might increase the velocity/pressure?

[Minnreefer]

Welcome to TRT. I was thinking a similar thing. The biggest problem is most pumps do not suck very well so they may have a problem getting the water up high enough to make a difference. Along the same lines, one could if they really wanted to use a few smaller pumps to pump the water up to a large storage area much higher above the tank and let gravity work for you. But that also brings up many more problems.

Keep thinking

Thanks and welcome to TRT

Jon