Backyard Aquaponics
A place to discuss aquaponics

I'm with SV here.
And have tested it myself.

Impellor water pump power consumption is directly related to impellor speed.

Put a pump in your tank with nothing connected, it will draw more than it is rated for.
Block the outlet and power draw drops.

Time to update the title again

When I started this thread yesterday I thought that it might be a useful place to critically examine any number of contentious issues, or myth/facts. Excluding pizza and beer (which aren't all that contentious) we have already covered four topics - depletion of dissolved O2 in pump water, aeroponics, the efficacy of eductors, and now pump power consumption under load. At this rate we might need a dedicated Myth or Fact discussion area - unless we all agree to stop disagreeing!





*edited under instruction from PJ - charlie*

Awww bugger! And here I was thinking I was super dooper smart?

Good thing all you smarties are here to set me straight, thankyou!

Guess I assumed when amps rise so did watts considering that amps x volts = watts. Or put in another term... flow x pressure = released energy.

Shame on me...

You are super dooper smart Charlie !


Correct. But we are saying that the amps are decreasing as the pumping head increases.


This also sounds ok. But when you increase the head you reduce the flow (if you increase the head a lot, flow totally stops) and therefore reduce the energy. Probabaly not a linear relationship though.

yeah we did a unit on pump selection and application at uni and it was covered in there that power usage decreases with pump output, just don't stall your pumps for too long it might start cavitating and damage your impeller.

thinking about it the 'expert' in the original post may have seen the bubbles created from cavitation and decided that it was the DO being pushed out of the water

what was your course, mech eng ?

yup

Eductors have been around for some

thanks SV and freebz!

phone cut me off. eductors have been around and made a big splash on reefcentral years ago. In the reefing world, flow is king, and energy conservation is a must, as heat is a reefer's worst enemy. For more real world reading material, search reefcentral for eductor and i'm sure you'll have lots of reading material. The flaw in our setups is that the drain has no water pressure to really make use of how the eductor works. And even if you sealed the connection to force some sort of pressure, you take on far too many risks of clogging the return pipe.

Ultimately, the goal was to increase water circulation, while not using much power. Although the eductor was large and unsightly, reefers were in fact using high pressure pumps as their return, which did suit this scenario. The water flow gain for an eductor is virtually impossible to measure, but ultimately the diy eductor threads eventually got completely destroyed with the invention of stream pumps. Stream pumps would take a standard 300gph maxijet and allow them to push 1400+ gph using simple toy kit impellers.

In today's world, you can buy simple off the shelf stream pumps for less than $70 and they'll easily push 2000 gph and consume less than 10 watts of electricity.

At one point i did some diy eductors years ago, and eventually bought some manufactured eductors. there was a brief window of popularity, but you rarely see any reef tank with an eductor anymore.

thanks toefu, that puts that topic at rest for me anyway

Cool video, and thanks for the info toefu!