How does it work? Vol 4: Eductors

[Moe_K]

Allrighty. Time for our weekly discussion.
The topic is "eductors."
Topics for the discussion might include: when to use an eductor; how much do they cost; where can an eductor be obtained; why would one use an eductor; and perhaps how to make a DIY eductor.
Feel free to evolve the discussion, but let us not stray too far from the topic.

Would somebody kindly help us out with a definition, and maybe a diagram or picture?

 

[PenMan]

interesting link on eductors.

http://themantledmonster.thereeftank.com/eductor.html

I looked into this a while ago and this was one of the best explainations that I could find.

 

[jango]

That pretty much sum's it up. Good article PenMan...

 

[Matt L.]

Eductors

I don't have my hydraulics text book in front of me, so I can't give you the actual definition right now, however, what the man in PenMan's link says is a very accurate description of what an eductor does.

How an eductor works is a little more complicated, and in short, the performance of an educotr revolves around the Venturi principle.

Water flowing axially into and then through the eductor creates a relative negative pressure at holes placed in the wall of the device. This negative pressure causes more flow to enter the eductor at these holes or ports, thereby creating a net increase in flow exiting the device compared to what entered at the beginning. Of course, conservation of mass and volume apply, so the water axially entering the eductor initially, plus the water pulled in through the side ports, equals the water discharged axially at the end of the eductor.

Matt

 

[littlep93056]

I used them before I got Tunzes, they work great if you use a pressure rated pump

 

[jango]

Water flowing axially into and then through the eductor creates a relative negative pressure at holes placed in the wall of the device. This negative pressure causes more flow to enter the eductor at these holes or ports, thereby creating a net increase in flow exiting the device compared to what entered at the beginning. Of course, conservation of mass and volume apply, so the water axially entering the eductor initially, plus the water pulled in through the side ports, equals the water discharged axially at the end of the eductor.

Matt

So in layman's term's, if you got enough pressure from your pump these thing's crank out some water...

 

[littlep93056]

You got it !!!!

 

[Moe_K]

From Penman's link...

An Eductor is a device that pulls water in from around its base and shoots it out its nozzle. When installed properly they are able to pump 4 to 5 times the volume of water entering the eductor. In order for Eductors to work properly they need a pump that can handle a lot of pressure. Eductors like to have pressure in the 10-50psi range to work most efficiently. 10psi equalls 23 feet of head pressure! that is a fairly powerfull pump. This pretty much eliminates any powerhead from being used with eductors. Luckily at this pressure the eductor only needs between 450 and 1000gph to work properly. Most pump that can reach 23 feet or higher of head pressure will be putting out at least 450gph.


This 4 to 5 times the volume is a little misleading. The eductor is multiplying the volume of water that is exiting the internal nozzle, not what the pumps total rating is. Lets use an Iwaki 70rlt as an example. It is rated at about 1600gph and maximum head of 31'. Lets say the eductor needs 23' of head pressure. At 23' of head pressure the Iwaki is pushing 700gph. Both of these fall with in the eductors ratings. We multiply the 700gph by 4 to get 2800gph leaving the eductor! You do not multiply the 1600gph rating times 4 to get the volume leaving the eductor.

An eductor works the same way as an open sunroof does on your car if you are driving on the highway. Have you ever noticed how people's hair sticks out of the sunroom at hightway speeds? This is the same principal that causes an eductor to work. The fast moving water is lower in pressure than the surrounding water causing the surrounding water to get pulled along with the fast moving water. This is occuring around the entire eductor so the total volume is increased many times.

 

[jango]

Good idea Moe..

 

[Matt L.]

So in layman's term's, if you got enough pressure from your pump these thing's crank out some water...

Yes,

but if you really wanted to be accurate, you would say that if you got enough flow from your pump entering the eductor, you get some serious flow exiting the eductor.

Matt

 

[nunofs]

A couple of places where to get them:

http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/9846/cid/2953
http://www.kthsales.com/website/Misc/hello_salt_water_enthusiasts.htm

Nuno

 

[jmkeary]

although it seems that these require 10-50psi to work most efficiently would they still work at lower psi? if you could get a X2 on the volume from a powerhead it could be worth the low cost of one of these.

 

[littlep93056]

heres a link to the ones I used

http://www.kthsales.com/website/Misc/hello_salt_water_enthusiasts.htm

there are charts on the flow

 

[NateHanson]

But I'll bet the backpressure the small apeture of an eductor puts on a non-pressure rated pump, would more than erradicate any gains in flow.

Even with a pressure rated pump, does that 4-5x flow figure compare the flow into the eductor with the flow out of the enductor? If so, you have to consider the reduced flow created by the pressure the enductor produces. In the link that Paul posted, the guy says an Iwaki 70 (which is rated at 1600gph) pushes 700gph at 10psi (the low end required for eductors). Then if the enductor magnifies flow four time, you'll have 2800gph coming out. That's less than a two-fold increase. It's still an increase, certainly, but not the 4-5x that is generally stated. It's like making a 20% return in the stock market, and conveniently ignoring the 15% your broker took off the top.

Is my reasoning correct?

 

[littlep93056]

Believe me they work great , I hope someone who uses them makes a post about how good they work

Nit Pic all you want about them but it's a very cheap way of getting a lot more flow

 

[Moe_K]

The flow from an eductor is just uni-directional, hunh?
Well, unless there's some modification to oscillate the nozzle, right?
Another consideration is the price of the pumps required.

 

[littlep93056]

They work on low flow pumps but not as good

 

[NateHanson]

Particularly with low flow pumps, does the increase in flow more than make up for the flow reduction caused by the narrow aperture of the eductor?

 

[Shallowwaters]

Could SeaSwirls could be modified to produce an eductor effect?

 

[littlep93056]

one of me penductors was on my sea swirl with a mag 24 worked great