Manifold design - push or pull?

[FSM]

I'm turning my 29 gallon into a river tank with a PVC manifold. The pump is a JBJ 2500 (550 GPH)

It would be a lot easier to diffuser the flow if I reverse the design in the article, and put the output opposite the pump. Is that going to reduce the flow though? Would it be more efficient to put the intake away from the pump, like the article shows?

[Diana]

That might be better answered by the manufacturer of the pump. Some might be better at pushing water through the pipes, so a simple filter over the inlet would create the least restriction on that side. Others might be better pulling the water through a filter, with as simple a discharge as possible.

It does not matter from the point of view of the river tank concept. The pump can be physically anywhere it needs to be for most efficient use. You can build a manifold as an intake or as an outlet. As far as hydraulics are concerned look at pipe sizing for maximum efficiency.
The most basic requirement is that inlet and outlet are at opposite ends of the tank. Beyond that, go with whatever you can dream up and design!

My river tank has a canister filter as part of the water flow, so in this case the pump is under the tank, not in it at all. The other part of the flow is a powerhead in the position shown in the river tank sketches, with sponge covered inlet at the other end.

[Emma Turner]

Hi FSM,
This old thread from Les on a type of reverse flow manifold may be of interest: http://forums.loaches.com/viewtopic.php?t=5750
Emma

[FSM]

after piecing together the PVC, it seems to cut down on the flow a lot, but that may just be because the output on the power head is a lot smaller than the PVC output I compared it to.

The powerhead comes with two output nozzles/intake covers, one has a single nozzle, the other has two, forming a right angle. I may just put a 90 on on nozzle so both are pointing in the same direction. With just the single nozzle, the flow isn't adequately diffused.

[Martin Thoene]

The question I would ask is, "Why?"

What sort of fish are you intending to keep? There's nothing wrong with having a concentrated flow exiting the powerhead as it allows fish to choose to sit in the high flow or lower flow areas.

Using the manifold as the design shows allows for multiple intake sponges which diffuses the "suck" at each one. This makes them far safer for fry (for instance) than a single sponge protecting the powerhead intake directly. It also increases greatly the available surface area available for beneficial bacteria to grow.

Martin.

[FSM]

Sewellia lineolata, probably.

With just one output most of the tank doesn't have much flow at all. I thought the point of the manifold was to create linear flow, instead of a circular (upper level of the tank flows the opposite direction from the bottom)

It looks like using the dual outputs works better, so I will probably just use that and not bother with the spray bar I originally planned.

[Diana]

It is indeed a matter of both intake and outlet.

An intake that is small can create a very strong suction, and can plug up too easily. A larger intake, or several smaller ones are safer for the fish, have less chance of plugging up, and can be arranged to enhance the flow.

An outlet that is one strong jet is not creating that uniform stream-like flow. If the output can be divided among several outlets, or a spraybar (or even a couple of them) then the flow will be more uniform through the tank.

Combine a larger intlet area, such as the whole end of the tank being a sponge with a multiple outlet manifold and the tank will approach that ideal of one mass of water moving. It will take a large volume pump to be able to move that much water. My river tank is moving the water at about 20 times the tank volume, and I think it is just about right, certainly I would not want it any less. 400 gallons per hour sounds like a lot of water movement in a 20 gallon tank, but the fish are right up there enjoying it.

A natural stream is not a smooth flow, it will have back waters, ripples, quiet spots, eddies... and so will even a very well designed tank. This is an invitation to design the best, though, not an excuse to get by with less. It is good that you are putting a lot of thought into how to make it work really well.

[FSM]

Sadly it seems that the manifold drastically cuts down on the flow either way. Maybe the pump is the problem; it probably isn't designed for high pressure applications like this. When I first started planning for the project I considered using a quietone pump like I have running the sump on another tank. The JBJ powerheads were cheap though, $19 each.

[Diana]

There are some pumps that really slow down when they are asked to do that sort of work. Might be a good idea to research pumps a bit, and find one that specializes in pumping water through pipes.
Perhaps a different pipe design would help, too.
Larger pipes, and fewer corners. Making the corners as rounded as possible.