Closed Loop

[JJ1234567]

could someone please explain what a closed loop is?

 

[Mr Miagi]

A closed loop system is a series of pumps (mainly one pump) and pipes for the movement of water only. No filtration takes place. An external pump pulls water from the tank, and passes it through plumbing, re-directing it in the desired direction. Just for flow. Hope that explains it.

 

[SkiFletch]

Yeah, in aquarium terms thats what it means. In engineering terms a closed loop system is one in which at no point is the fluid being pumped exposed to open atmosphere. Anything with an open resevior (like a fishtank) to an engineer means an open looped system. We have no need for engineering closed loop systems since we're always doing something to our water

 

[crazyelece]

They are used to create custom flow patterns in the tank instead of using powerheads. A typical style is one drain line to a pump which the output then splits in two and comes back to either side of the tank. When run through bulkhead fittings, all the plumbing and pumps are outside of the tank so that the tank looks less cluttered but you can get much more flow and control it better than by using powerheads.

 

[Aquascaper]

It's a big external powerhead in laymans terms

As the others have said - water is drawn from the tank to an inline pump then it is piped back into the tank through various nozzles to create multiple flow patterns. Very good if you have a big tank as you can achieve good flow without having huge powerheads on display in the main tank or having to try and hide them somehow. In really big tanks people generally drill through the bottom of the tank and have nozzles along the front pointing back at the reef which they hide with chunks of live rock....looks awesome

I ran a 5000lph (1320gph) inline/submersible pump in my 120g tank linked to two 2' spraybars that ran down the front corners of the tank which I then hid by running wood strips on the outside of the front corners of the tank. This created a constant stream of water across the live rock wall which was disrupted in points with smaller powerheads that were easily hidden in the rockwork.

IMO it's not really worth doing in a small tank (under 40g) as the pipework would just get in the way and the powerheads used on tanks of this size are relativley easy to hide anyway, that is of course unless you drilled the tank.

 

[prios]

This is something I plan on doing to a 75 gallon. Can you recommend a particular pump? Doesn't need to be a very powerful flow as it will be fish only with some live rock.

 

[SkiFletch]

Well, it depends on where you want to mount the pump... For every foot below the water line in a system thats exposed to ambient (an aquarium tank) your pump needs to work harder. If its only going to be a couple feet below the waterline you should be OK with say a Danner Mag 7. If we're talking like 4 feet below the water line, then you're going to want to look into something like an Iwaki 20MDZ

 

[SkiFletch]

Just to add, when looking for a pump, find its pump curve or presure curve. Decide how much flowrate you want, and see if the pump can deliver it over the head loss (distance from water level to pump). For example, look at this graph with pump curves for Iwaki pump models:

Lets say you have 4 feet of head loss (distance from water line to pump mount labeled TDH here). Lets also say that you want 8gpm (480gph) of flowrate. So you go to that point on the graph and see that the Iwaki 20RXT can provide that performance. Then lets say with that same head loss you want 20gpm. In order to get there, you'd need to go with a 40RXT. Conversely lets say that you still want that 20gpm but now your pump is 6 feet below the water line. In this instance you'd want a 70RT.

Every pump has a specific pump (performance) curve for flow versus feet of head (or sometimes pressure in psi). Make sure yours matches what you want to do and get that one

 

[Aquascaper]

Or hide the pump in the tank under a load of rock, wait until something crawls into it and jams it up then dismantle the whole reef to get the pump out and free it. After all that decide that it probably would be better to have it outside the tank after all

Or was that just me? Lesson learnt

 

[superman]

The mag7 or a Iwaki 20MDZ on a closed loop would only be for a very low flow tank. A dear friend of mine has a 75 gallon with a Sequence Dart on the closed loop, and I must say that it is all the flow he needs. You could then use a panworld 100PX-X as your sump pump and you will never want for any more flow. If you are going for a seahorse tank then you could do that mag7 on a closed loop, but even in a seahorse tank you may want more flow than that.