I've heard about closed loops....

[PeeJ]

Several folks have mentioned something to the effect that closed loops have no head pressure....this seems false.

What's the scoop? Seems like a pump (rather being on a closed loop or not) pumping upwards will have head pressure.

[Ram_Puppy]

Peej, A closed loop originates in the main tank, and dumps into the main tank, it is essentially there for water movement, you don't need a pump rated for head pressure because your not moving your water vertically, as I understand it. THink of it as taking water out of the left side of the tank, and putting it back in on the right side.

I hope I got that right! :)

[brewercm]

The head pressure will be greatly reduced because it isn't a return from a sump but from basically a siphon type feed in.

[PeeJ]

Well I mean the water still has to go from the tank, down the the floor, and then the pump back up to the top of the tank. So on an Mag18 what should I expect to acutally see? I'm doing the Calfo "retrun manifold" for the closed loop and am trying to figure how many and what size outlets to use.

I'm thinking I am just going to drill 1/2 inch holes in the pipe and regular intervals. Basically the entire rim of the tank will be a big spray bar with holes at different angles. Figure this would work great.

[dan]

if your pump is setting on the floor than there is head pressure to push whatever hight the entry is in the tank. example: if the pump on the floor and the entry to the close loop is 4 feet than you have 4 feet head pressure. the only time you have no head pressure is when you mount the pump horizonal with the drain.

[PeeJ]

Well at any rate does the Mag 18 on a closed loop with a 1000 GPH for return sound like enough flow for a 100 gallon tank?

[NaCl_H2O]

Actually, head pressure is measured in the # of feet of water the pump must displace. If you pump water in a closed loop in & out of the aquarium at the same height, but have 3' of water in your tank above the return, you still have 3' of head pressure!

Measure the distance from the pump outlet to the highest point of your return plumbing (if return is over the top of aquarium), or to the aquarium water line (if return is below water line).

That is actualy a pretty gross measurement, pipe diameter, number of elbows, pipe resistance, and other factors also come into play. Just add a little to the gross measurement and check the pump curves. Some pumps drop off drastically above 4-6 ft of head pressure!!

[PeeJ]

Hmmm...I have to go up about 5 feet...that equates to 1200 GPH on the mag 18....that doesn't appear to be enough flow.

[prof]

1200gph is a substantial amout of water. You can influence the power of the water leaving your pipes by using a smaller diameter pipe.

[PeeJ]

Yeah I suppose. I mean I could do the Mag18 on a closed loop or go with 6 Maxi-Jet 1200s.

If I mount the Mag 18 to the center brace of my stand up at the top, I can probably get about 1600 GPH out of it. You know? Bolt it to the the 1x4 in the back of my stand. That would leave about 2 feet of head. What do you think about that?

[GaryP]

PeeJ,

Have you seen the closed loop in the SPS tank at aquatic warehouse? The pump is sitting on the crossbar. It basically picks up the water and pumps it back in at the same level. Of course there is some loss due to elbows and a little bit of friction, but this should be a small loss.

I currently have 4 X MJ 1200 in my 125 gal. and it gives me plenty of flow.

Gary

[matt]

Josh got it right. Head pressure is measured from water level to water level. If your drain and return for a closed loop is submerged in the same tank, there is no head pressure, regardless of where the pump is. Think about if you were to shut off the pump in a closed loop. The water in the return hose will not drain back to the pump, both drain and return lines will stay filled. In an "open" loop, like sump to tank, you measure the sump water level to the tank water level. That's your head pressure.

But, there are major factors of frictional pressure involved. There's a good calculator on reef central for this. For instance, running a mag pump with 6 ft of 3/4" line as opposed to 6 ft of 1" line will really cut down the pump output. And trying to figure actual output with a mag pump is probably a bit difficult, because they are so over rated for flow. I recently saw a friend's mag 18 pumping water out of a sump into a tank about 5 ft up, using 3/4" line split into 2 3/4" lines. I couldn't believe how little flow there was; nowhere near as much as I get with my pan world pump rated at 790 gph.

[PeeJ]

Thanks for sharing that last bit matt. Would an AmpMaster 2100 be too much? Seems like a bullet proof pump that i could use for quite some time