Ok Snowboss. You seem to be confident in you're figuring. I can only pull the water in my 10 gallon USD tank about 7 inches up till there are no more bubbles, the venturi stops working. I'll set up the little 3/4 gallon tank as an USD tank tomorrow and we'll see if I can get the water to suck to the top with the venturi. This tank is much narrower so it should work if you are right.

If you're right you're the man!

Spongbob. The vacuum at the top of the USD tank is so strong that it makes the venturi stop working. Try taking a powerhead with attached venturi air line and submerge it into deep water. hold it at the bottom of the tank and see if it still works. There's only so much vacuum in a given venturi. Exceed that and it stops working.

now - -i have a question as I've never tried this.....if the power head is adjustable {flow wise} in theory if you run it wide open it should pull more vacuum ...no?

also PK try this for me . . .when i worked in the petroleum industry we had a submersable fuel pump system that used a venturi for leak detection - -basically a 2 horsepower pump pushing through a venturi with a vaccum controlled diaphram valve on it - - -you could adjust the venturi according to line size and distance we were pushing fuel {calibrating it basically} and with the pump running wide open we would restrict the venturi to create more vaccum..........if a hole occured in the line it would break the vaccum and the valve would close, limiting fuel spillage into the ground......

so try to restrict the opening of the power head little by little and see if you can't pull more head on the UDT...................just a thought

you might end up with a bubble problem .....and/or premature powerhead failure though ....as they don't come in a 2 horsepower model yet....lol but i think the theory is still solid

good luck man ....Boss

drop me a PM with your regular e-mail addy - -i have a couple scetches i want to send you on monday from my office computer of a venturi sytem that might work better for you and not depend on the internals of a powerhead....

I think bos smight have a good idea by running the powerhead at full capacity and restricting the amount of air it tries to take from the venturi, if I read him right. Powerheads gph are depleted by use of venturi (aquaclear even told me this) I think my little AC20 caps out at 128gph and with venturi is closer to 100. The amount that's variable between those two numbers probably depends on the volume of air you're trying to suck. lol
So perhaps running the phead at full pressure and limiting the air you try to pull will allow it to pull more air at a higher pressure? I hope that made sense. I barely understood all the stuff boss was talkin about earlier. lol
Sorry for your loss, as well.

N/P bud....just trying to look out for ya...I'm very interested in seeing this thing work successfully,safely and dependably .........

the scetches I wanted to send you were of a large venturi system {well large for a fish tank, lol}

if you take a PH without a venturi on it run it into a hose or pvc pipe say an inch long then glue on a "Y" pipe {like a sewer clean out} with the Y making an arrow in the out direction now glue a 5-6 inch piece of hose or pvc striaght out and run pvc or hose out of the Y up into the USDT ....this should create a large vaccum and when the air is sucked out it just becomes a circulation pump..............i would think this should all be in about 3/8ths pipe or hose ...which should way outperform the 1/8 th inch ID of a powerhead venturi...no???

i believe your onto something there .........a 3/8 by 3/4 pvc bushing glued into a 3/4 pvc pipe......with a 3/8 nipple inside, power head on the outside and run the air line into it like you stated above...........BAM, instant upside down tank suctionizer , lol ...................Boss