Closed loop question.

[Masterderrull]

If I have a closed loop, but pump is under the tank (in the stand), and the intake for the pump is at the same level as 2 outputs but higher than the other 2 outlets; do I have to acount for head hieght at all? I know is sounds confusing and it is, but I want to buy the right pump.

Also, how much flow for an OM4 should I have in a 90gal tank?
Thanks for everyones input.

 

[sokin]

You could drop Paul a line, you can find his contact info on his site. When I talked to him awhile back he said the Dart works great on the 4-ways and 8-ways. Prob to much for your 90 thou. He also has a forum on his site. Drop him a line and he will help you out.

http://www.oceansmotions.com/forum/

 

[Raceimage]

you can always put a ball valve on the output side of the pump to regulate the flow if your pump is too big.

 

[cdalmost]

In The Reef Aquarium, Vol 3, on p.109, Delbeek and Sprung write, "If you are drawing water directly from the tank [... and] returning water to the tank below the surface, you need to add this distance below the surface to the vertical head pressure since the pump has to work against the water height."

Basically, all four outlets, assuming they are below the water surface, need to be counted when calculating head pressure. The amount is simply the distance from the surface to the outlet in each case. After adding the head from the pumping (negligible if you are using great enough diameter pipe) and the OM4, you will be ready to pick a pump. With that I have no experience.

 

[BeanAnimal]

Messers Delbeek and Sprung are simply not correct:

By its very definition a "closed loop" has zero static head pressure. Both the discharge and suction are to/from the same pool and thus any pressure (head height) pressing against the discharge is cancled by the same pressure pushing against the suction. Therefore, the only "head loss" in the system is that of the plumbing itself. This section of the book needs to be ignored, now matter how much we respect the (other) well formed opinions of those who published the book.

Lets take a 100' tall "tank" with (3) closed loops. Lets assume the pumps are rated at 1000 GPH at 0' of head. The first "loop" intakes from 1' below the surface and the discharges at the BOTTOM of the tank. The second loop intakes from the BOTTOM of the tank and discharges 1' below the surface. The third loop intakes and discharged at the 50' mark. That means that all (3) pumps have roughly 100' of plumbing (each). Each pump will flow exactly the same volume of water. The flow rate would be calculated by determining the head loss in 100' of plumbing (due to friction).

The location of the pump in relation to the pool is also not relevant, as long as both the suction and discharge are in the same pool. This works even of the pump is ABOVE the water line of the pool (though it has to be primed to operate).

Hope that helps

 

[cdalmost]

Bill, in that section they do not explicitly discuss "closed loop" systems and it is likely that I simply misinterpreted the ambiguous wording "If you are drawing water directly from the tank..." What other advice in that section on calculating pump head loss would you say is also substantially off? This is the only book I own that discusses plumbing in any detail.

Back on topic, no, because the loop is closed you don't have to account for static head. However you still need to account for loss due to the device itself, friction in the pipe, and the myriad plumbing fittings needed to get it hooked up.

 

[BeanAnimal]

Chris,

I don't think you erred in interpretation of the wording though I do not appear to be able to find my copy to reference. Reading the citation you posted it does appear that you interpreted the passage as intended and the mistake is theirs, not yours.

If you remember, bring that puppy along to the meeting so we can take a look. I should have said to ignore the "passage" not the entire section, as I would bet that the bulk of the advice is sound.

FWIW, the "must have" aquarium plumbing (physics) book for aquarists is "Aquatic Systems Engineering" by P.R. ESCOBAL. I paid nearly $100 for my copy (they are rare) and to my astonishment found that the ENTIRE chapter on heating (thermodynamics) is built upon a single complex mathematical integration where Mr. Escobal neglected to convert units in one of the first order terms of said equation. The result is that for tank sizes close to ones used to demonstrate the equation, the resulting thermal output is close to what one would expect. For tank sizes that fall on either side of the examples the equation returns results that are several orders of magnitude too large. The author nor the editor caught the mistake in two editions of publication! I caught it when building a similar equation and checking his as a reference. Most reefers use his work as a reference and pass his equations and formulas along as authoritative advice. It should be pointed out that P.R. Escobal is a noted author in the field of orbital mechanics and likely knows more about physics (and thermodynamics) than I could ever dream of knowing. I guess anybody can make a mistake that is published and passed on as knowledge

Lastly, I think if you look hard enough (please don't ) at some of my early posts here at RC, I passed on the same advice regarding head and closed loops (several times) until an engineer corrected me.