Intake plumbing redo

1" pipe is .785 sq " cross section

2" pipe is ~3.14 sq " cross section

Right now you have .785 sq", plus head pressure from both streams crashing into each other and then making a right turn into the pipe inlet.

Option 1 will get you to 1/2 of the 2" pipe's cross sectional area. If you use something like a squid ( 4 or 5 1" inputs to a 2" pipe ) then you've doubled your area and I would expect flow to roughly double instead of just a 25% increase as long as you don't do any right angle bends in there like you have with the T fitting.

Option 2 could theoretically give you full flow in the system with a squid, but if you EVER lose siphon ( unlikely with that kind of flow ) you're in for a world of hurt. This ALSO assumes that you run some kind of herbie setup, or something that otherwise gets rid of the air, so that you don't have a lot of air injected into your pump intake from the water crashing down the overflows. Using a durso standpipe or similar will inject massive amounts of air. This will cause you some grief in the pump.

Other ideas:

Option 3. Add another bulkhead? 1.5" maybe? That's 1.75 sq" cross section. Plumb that in and you've exceeded the pumps intake cross section. < - good thing.

Option 4. Alternately, skip the overflow. If you have bulkheads already, just run one or two complete siphon tubes over the side and skip the overflow idea. No air to suck in. The predrilled bulkheads seem to indicate you're using closed loop anyway so no risk of flooding. With that kind of flow any siphon breakl/leak is likely to just suck the air along into the pump and be expelled so the two overhanging siphons might even be self priming as long as their intakes stay underwater. Since it isn't a constant massive injection of air you will likely be fine. You could just do the 1.5" over the top siphon tube either with your 1" pipes or run 2 of them and just use your existing bulkheads for a different loop. The white PVC could be painted, or possibly dyed black and you won't see it.

Option 6. Run a 2" siphon tube over the side and be done with it and use the 1" bulkheads for something else.

Option 7+. Stuff we haven't even thought of yet.

Hopefully that can give you some ideas.

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S

 

How's it coming? What did you decide on?

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S

 

The siphon would just be a tube from your 2" to 5 way 1" cone or some other fitting arrangement going over the top of the tank in the usual U shape.

To start it there's two ways I can think of leading to a third idea.

One would be to stuff a bit of airline into the tube up to the top and then suck out the air to get it going, this sometimes imparts a bad taste directly on your tongue.

Another method was to have a way to pour water into it but this requires extra fittings and may allow air leaks in. The air leaks. if small enough, might not be a big deal since the tiny bubbles would just get dragged on through the pump so you probably wouldn't break the siphon since the bubbles couldn't build up.

I was kind of banking on this idea as a third method. If you look at how the hang on back filters work, with a little water in the impeller chamber it slowly sucks out air in little spurts and draws the water up the tube as it gets rid of the air. In your case I was figuring that since you'd have the two direct feeds from the bulkheads you'd have a flooded pump so those feeds would work no matter what. After that, the other feed into the pump, the over the top feed, would have the air drawn out by venturi action from the other two feeds in the cone fitting and slowly purge the air out. Eventually you'd get enough air out of the tube like the HOB filters and then whoosh, the siphon would start. You'd have bubbles everywhere for a few minutes but at that point you're primed and good to go. If the intake is low enough in the tank you may never lose prime. But if I'm right, you'd have a self priming siphon anyway so it wouldn't be that big a deal if you did. Sadly the only way I can think of to prove it would be to actually try it, but if you're going to cap off those inlets anyway it should hopefully be easy enough to try and cost very little. Putting your hand over the inlet should prove if it's working, or the large tornado in the tank from all the extra flow might prove it as well.

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S