+1 to that idea. Prevents backflow, and gravity assisting the water coming down should provide plenty of pressure to trigger the valve the right direction.
Ya now I just have to find one that works with a downward flow.....
you could always isolate the two sides completely, so that they are physically connected, but not in terms of flow, with 2 intakes and 2 returns... just seal off the center piece between the hydors. this might not be ideal aesthetically, but would eliminate the need for a check valve without adding any more restriction to the flow.
If I seperate the two, then I have entirely defeated the purpose for plumbing them both together to begin with.... so that they can both work to overcome the 5' or so of pipe that they need to push water though (each filter only has 4' of head)..... its a small attempt at giving more head pressure with both filters working together on a single line.
If I seperate trhem then I run into:
buying two more intake/outputs
having two more intakes/outputs in my tank.
having to buy more fittings, and running more pipe.
still having a longer run of pipe on the output side, than each single filter can push through.
A couple things:
Every angle that you have in your plumbing is reducing your water flow, so you're not going to get anywhere near 232 gph. With 8' of head pressure, it is unlikely that you're going to have enough flow through the filters.
I would install check valves after each filter to prevent pressure from the other filter from restricting it's flow further.
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=3627&N=2004+113427
or
http://www.aquariumguys.com/oceanclear.html
would be a viable option for what you want to do.
Considering the price of the two eheims and two hydors, it wouldn't be that much different in price.
Im aware of restrictions, read a few posts back... i mention it.
installing check valves after each filter wont work, because I need spring loaded ones, and they will further reduce the amount of flow coming out of the filters.
There is not 8' of head pressure pushing back on the filters, there should be 8' of head coming out of the two filters.
Each filter has 4' of head, with a 3/8" output. both filters are connected at the outputs, before the Hydors, so this should hopefully have enough pressure to actually keep the water flowing through the 5' of pipe or so.
being that its 1/2" though, there will be more water weight pushing back on the filters, but again, this will hopefully be divided amongst the two, actually providing no more water weight, at the filter output, than there would normally be with 3/8" tubing. IE, I will likely have the same flowrate as a single filter, but double the pressure.
also as mentioned, I may end up buying a water pump to boost it along anyway. And I will be installing a flowmeter along the output side as well so I know how much water im turning over.
As for buying yet another filter..... why would I waste the money to buy another filter thats the same cost as the ones ive ALREADY purchased?
seems redundant, and holds me back more.
This system will work, and I should end up with somewhere above 100gph overall flow, without the addition of another pump to boost it.