Backyard Aquaponics
A place to discuss aquaponics

i found this when i googled "fish aeration".

it seems to be pretty powerful & it runs on 12 volts- no worries about power failures.

do you think this would be usefull in our hobby?
http://keepalive.net/portable.htm

the link shows what looks like a standard 12 volt bilge pump. I have tried to use them as sump pumps in evaporative cooling and in auquaphonics. They will last no more than six months in my experience. Even with a one amp fuse protection, the motor burns out then takes out the fuse. They are to expensive and short lived. I now use AC mag pumps and a sine wave invertor. The mag pumps draw little more power cost about the same and are rebuildable. You wont get reliable service from the mag pump with a nodified sine wave invertor.

Hey SR I'm confused by your last sentence - you're saying an AC pump through an inverter won't last unless it's a sine wave?

You can make any pump aerate your water in this fashion. You just need to introduce a small amount of air into the intake/ suction side of the pump. I did it by drilling a 1/4" hole on the intake side of my pump and putting a tube to a small pin valve. You have to be carefuller not to add too much air or the pump will not work. The blades of the pump will blend the air into the water going out. i did this on a small fish tank pump and it worked great.

The air bubbles hitting the blade of the pump with slowly wreak it. Even the pumps for protien skimmers that are designed for the blades to break up the air have to be changed after a while.

Never heard of that. Wonder how long it would take?

MM,
It's called CAVITATION and it is deadly for all non-positive displacement pumps (ie Centrifugal or Turbine) and most Rotating shaft positive displacement pumps as well.. This is why so much time and effort is spent on getting a good seal around the Pump shaft with Mechanical seals, lip seals and even packed Glands; to prevent any form of air entry or vacuums which causes cavitation. It can also occur if a pump is trying to draw more suction head than it can support. The impeller becomes pitted by the air under negative pressure and will eventually "corrode" and fail by breaking up, thus ruining the pump housing and flow outlet. This can take a week or a month depending on the duty. You will also notice a distinct decrease in output Flow and Pressure until both become nil. Why spend good money on a pump to do a duty and then completely destroy any chance the pump has of fulfilling that duty by encouraging Cavitation?
Get a seperate air pump/venturi/difusser and let your water pump do what it was designed for, pump water, not air!

Cheers IanK

Don't waste your money.

I also agree. Introducing are on a centripetal pump will greatly shorten it's life span. The cavitation is basically vibrate the bearings and wear them out faster. On many mag drive pumps, there are simple sleeves that act as bearings and the water acts as the lubrication. Once there is a bit of slop on the bearings, the impellers will start to hit against the pump casing. I've seen a lot of liquid ends destroyed by cavitation.

(shameless plug: I work for Iwaki America, who manufactures mag drive pumps )

There are two types of cavitation. Inertial Cavitation is the formation of bubbles in a liquid when the pressure of a liquid falls below the vapor pressure of the liquid. This is often a problem with high speed boats when the prop starts to cavitate there is a decrease in thrust and increase in vibration and prop damage. In this case we are introducing air into the system and mixing it up with the impeller of the pump. This could be called non inertial cavitation which is not nearly as destructive as Inertial Cavitation. Vibration will probably occur causing damage it will just take a lot longer with this setup. Im not sure if the impeller in a small pump like we use has enough force to cause destructive cavitation at all. I guess we will have to try and see if there is a problem. I have several small bilge pumps that i can try this on. I will propose an experiment. I will take my pump and photograph and examine the impeller. Then I will introduce air in to the intake and run it like that for a month. Then check it again. If no damage occurs then I will run it for another month and so on until failure or I get board.

This is the pump and how it is working.

the pump is a little dirty but works fine. I really should have at least 4 pumps 2 normal and2 with the air setup.

Why not just run a 30-40w four outlet mag airpump????

you are right after working on this thing for hours I have decided that it is too inefficient to be worth using anyway. I cant get it to run well continuously with the tools and parts I have on hand. I am scrapping the experiment. I know it can be done but I dont really want to spend the time to do it. Sorry

This is from my experiance with low votage motors (with brushes) The heat that they generate inside there waterproof container usally causes the seals to leak, the few different ones ive tried have all died in the same manner. My thoughts are dont rely on them, might be ok for back up purposes though