coolcol said:
Wel well well........now thats great info guys......lots of explainations, Am not an engineer like some of you fellas but I know that even the best needle wheel cant compete with a standard impeller for creating the flow needed to activate a venturi device....these needle wheel impellers are designed tho chop the air up more than circulate it, so any pulling power to offset the height of water would be seriously compromised i would imagine.
The info from ldrhawke(john) was interesting but still leaves me guessing at what best to do.......ah well .....only one way to find out....
A lot of venturi's are designed to perform at 15 to 20 psig.....35' to 45' of head was interesting.....most of our pumps cant approach that sort of pressure.....mind you the new downdraft skimmers use very powerful high pressure pumps to inject water...what sort of head would they produce do you reckon ldrhawke(john).....
Often the problem is trying to use on pump for two different purposes with two totally different needs, 1) flow rate and 2)fine bubbles. It can be done but it is balancing act if you try to do it with one device. Selecting a single pump to make fine bubbles and also supply a uniform flow rate can be a tricky.
Using a single device for both flow( thru the skimmer) and pressure ( making bubbles) can complicate balancing and tuning a skimmer. If you try to increase the pressure to make fine bubbles, you also increase the flow thru and levels skimmer. If you decrease the flow you may not be making fine bubbles.
The insump ER skimmer solves the flow problem by not having any back pressure into the sump to restrict the flow, and use the single little pinwheel for both flow and aeration. The flow is unimpeded.
When you put the same skimmer outside the sump, you need to configure return piping which can be different for everyone, so it has no restriction. This can become a problem because a slight increase in restriction to flow can dramatically effect flow and level in the skimmer. An outside the sump skimmer is easier to set up using two independent devices, one for bubbles and one for flow. It is much easier to optimize perfomance with two independent devices for flow and bubbles.
I am running leak and bench tests on my skimmer as I write this. I initally had it set up with two Sedra 900 pumps; one pin wheel for bubbles and one for flow (with an mazzei injector attached). While testing I found out I don't need, or even want, the additional bubbles from the mazzei. The Sedra 900 pinwheel air flow has to be restricted way down or it produces too much foam. When I ran it with both ejectors, the foam virtaully forced the collection cup cap off the top. I have to set a couple of pound weight on the cap to keep it in place when running the air wide open on the Sedra 900 pinwheel or it will blow foam all over the kitchen.
I no longer have a need for a high pressure pump feeding or the mazzei injector. I changed to smaller Sedra for flow that only pulls less than 20 watts to feed 4 to 5 gpm. It also saved energy and reduced a lot of heat energy being dumped into the water I had with the additional Sedra 900. I could do that easily if the system was run with a single pump. After recirculating for hours into the small test sump I see a very little temperature rise.
If you select and skimmer that uses a single pump for both make sure you use the exact pump recommended by the mfg. that he has tested, and make sure if it is an out side skimmer the return flow is not restricted in anyway. It should be virtually gravity feed into the sump.
