Questions about Sumps [retitled]

[Thales]

I've never wanted a sump because all the horror stories I've read about when a power failure occurs like the main tank water being siphoned down to the sump and overflowing it all over the floor. I'm not extremely knowledgable on sumps but how do you avoid the power failure overflow nightmare when the return pump has no power?

Funny, I just revamped a system at a wholesaler because they were getting floods when they turned off their main return pump!
I think floods are actually easy to avoid, and any horror stories are most likely from people who didn't really understand the whys or hows of sumps in the first place. Its just one of those things I was talking about that once understood, seems obvious.
As sump is a volume of water external from the main tank. Usually it is under the tank. You put all your filtration, heaters, carbon, skimmers and whatnot into the sump so you don't have to look at them in the main tank, and you get a larger water volume in the system which give you a more stable system. For a ceph, you also get the added benefit of having less equipment going into the tank that needs to be octo proofed.
So, you have a line from the tank to the sump (either drilled into the side or back, drilled into the bottom with a stand pipe, drilled into the bottom but in an overflow, or in the form of an external hang on overflow), and a return pump in the sump (or external, depending on choice) that pumps water back up to the tank. Generally these are called a return, as in return to tank, and overflow because the water level needs to reach a certain height for the water to overflow into that line to the sump.
Placement of the return and 'overflow' are important. When the power goes out, water will siphon from the tank into the sump via both the return and the overflow, and will drain as much water as their placement allows. If they have been placed as to allow more water to siphon than the sump will allow - boom, wet floors.
Most often this problem is not from the overflow because the overflow needs water pumping into the tank to, well, overflow. The flooding is almost always from the return being plumbed low in the tank. If the return is 2 inches below the surface of the water in the tank, in a power outage, it will drain the tank to that level. If the return is 1/4 inch below the surface of the water in the tank, in a power outage it will drain the tank to that level. Obviously, the return that is two inches below the water line will drain more water than the return that is 1/4 inch below the water line. In the power outage, the return that drains the tank two inches down also exposes to air anything in the top two inches of the tank - with a ceph not so bad, with corals really bad.
I don't trust things like check valves or anti siphon holes on the return lines. Check valves almost always fail because stuff grows on the surface of anything in saltwater, which will make the check valve not seal and the water will drain. Anti siphon holes get overgrown with muck or coraline algae and need to be tended regularly.
I like to idiot proof my systems so, the returns generally go way up high near the surface of the water. I also use the largest sumps I can and generally run them at a maximum of 1/2 volume so even if some jinky return I set up on the fly slips and is two or three inches below the waterline, the sump can handle it. And, I make sure to power outage test the system to make sure the sump can handle the volume drained into it in an outage.

Whew!

 

[Thales]

This kind of talk is so much more fun/rewarding with people who have done some legwork on their own!

Thanks guys. Your points, particularly regarding newbies, is exactly what I haven't started a "is there a step-by-step guide to setting up a reef tank" thread. I know all the pieces are here, or linked here from other sites, I've just got to ask the magic 8 ball that is TONMO the right questions and all will be revealed.

Whoo hoo!

I know I want to setup a complete and correct system from day 1, and not short-step anything, I know I want to properly cycle my system for as long as necessary, even though I also know that can mean a relatively non-rewarding period of time...The reward will come when I put in my first few "test" species and have great success with them because I was willing to do my homework and be patient and do it right the first time.

Thats fantastic. However, what you will find frustrating is there is no correct system. There are a bagillion ways to get any of this done and everyone has an opinion as to why to do what they do. You have to decide what you think will work best for you, and try to leave room for changes down the road.

I've been wanting to keep Cephs for many, many years now, and have had tremendous success with tropicals in the meantime, waiting to find a site like this where people like Rich and Jen, etc. were having luck with Cephs. I've bought a few books regarding new marine reef setup and have been reading them non-stop, when not researching points the book skips over online...

I think that experience puts you in really good shape.

I still have a lot to learn regarding the external filtration systems available and their benefits and detriments to our specific application here. Things like what makes a good protein skimmer,

Much debated topic. I like Euro Reefs or ASM's (ASM's are a Euro Reef knock off and are much cheaper)

how to properly setup the sump,

whether to use a trickle filter or a canister (likely both),

I run neither!

and how to make that work properly with a large refugium,

Why do you want a fuge? As an algae filter? I haven't found them necessary for ceph tanks or reef tanks - though they are in vogue.

as well as having space for hatching babies

Maybe in the fuge?

, staging them before release into the (likely 90G bow) main tank, quarantine, as well as extra space for last minute visitors.

All good stuff if you have the space.

Just a while longer, just a few more weeks' researching, and I'll be ready to start my build. Hopefully by next year's crop of babies I'll have a ground-up custom (and cycled) system ready and waiting to fulfill what now seems almost like a lifelong dream.

You are well on your way, and I can't wait to see what you come up with!

 

[monty]

Hey, as long as you guys are writing awesome sump articles, I have what's probably a really silly question:

why don't people just plumb a big vertical vent pipe into the return line? Then there will be no siphon vacuum if the return pump fails, and water in that vent pipe will rise to the same level as the tank water, so it can never overflow the vertical pipe (assuming all pipes are big enough diameter compared to the pump's max flow rate that resistance is negligible) but there can never be a siphon on the return. Of course, having a big vertical mast next to your tank may be kinda ugly.

Am I missing something painfully obvious?

 

[DHyslop]

Monty,

I'm not quite sure what you're asking. The return line is pressurized, so the water level in a vent pipe would try to rise to the hydraulic head of the pump, usually >15 ft. If the vent pipe was lower than that water would spray out. If the vent pipe was higher than that, it probably has more volume of water to go into the sump than the tank.

Dan

 

[Thales]

I guess if you made the mast tall enough it would work, but I think you would then have the pump fighting against the pressure the mast was creating.
People drill 'anti siphon' holes just over the waterline of the return, so if the power goes out, they suck air and break the siphon. They really only work with short runs of tubing though.

 

[monty]

Monty,

I'm not quite sure what you're asking. The return line is pressurized, so the water level in a vent pipe would try to rise to the hydraulic head of the pump, usually >15 ft. If the vent pipe was lower than that water would spray out. If the vent pipe was higher than that, it probably has more volume of water to go into the sump than the tank.

Dan

I think you got the question right-- I didn't think the pressure had to be that high in the return line. My thinking (which, like I said, is probably wrong) was that the water in the vertical vent pipe would seek the same level as in the main tank, because it's connected with a pretty large (hence low resistance) pipe. Isn't the hydraulic head the height that the pump could reach if it were just pumping into a vertical pipe that has no outlet except at the top, before the backpressure from the weight of the water offsets the pump's capacity, or am I misunderstanding the term? I'd think that the flow from the vent pipe into the tank into the overflow would relieve pressure far before it could build up a head of more than a few inches unless the return pump was a NASA surplus or something. Pascal's Principle (and his barrel experiment) show that the pressure in a vertical standpipe can be enormous even in a narrow pipe, so I'd think that the pipe between the vent and the tank would relieve the pressure far before a vertical head built up, unless that section were clogged (in which case I guess a pipe less than 15' would become a fountain, which is not so hot, but in the non-vented system it would build up a huge amount of backpressure and probably either stress the pump to death or burst some component, wouldn't it?)

Of course, despite having some confidence in my engineering reasoning, I also assume people don't do this because my reasoning doesn't apply somehow, so I'm not sure how to say the above without sounding irrationally overconfident... I'm probably just thinking about the problem wrong somehow, and maybe I'm just not getting your explanation because I'm thick.

 

[magikceph]

is a sump neccassary for a tank of bandensis?

 

[cuttlegirl]

No, a sump is not necessary, but it does make things easier. Do you have access to a local fish store that has salt water aquariums in your area? I think if you could go to a store and see what we are talking about you might be able to understand the basic setup of a salt water tank.

Also, is there a public aquarium in your area? You could learn sooo much by volunteering at an aquarium. This is how I started learning about salt water aquariums, the staff have a wealth of information and tips about caring for salt water animals.

 

[DHyslop]

I'd think that the flow from the vent pipe into the tank into the overflow would relieve pressure far before it could build up a head of more than a few inches unless the return pump was a NASA surplus or something. Pascal's Principle (and his barrel experiment) show that the pressure in a vertical standpipe can be enormous even in a narrow pipe, so I'd think that the pipe between the vent and the tank would relieve the pressure far before a vertical head built up, unless that section were clogged (in which case I guess a pipe less than 15' would become a fountain, which is not so hot, but in the non-vented system it would build up a huge amount of backpressure and probably either stress the pump to death or burst some component, wouldn't it?)

You're right that the height of water in the column would be lower than the pump's theoretical max head pressure because water is being bled off into the tank. The water level will be somewhere between that value and the height of the return. I suspect the water level will be much more than just a few inches above the return due to the degree the pump pressurizes the line (these are centripetal "high-pressure" pumps rather than axial "high-flow" pumps like NASA turbomachinery . Also given that return outlets are usually pinched off or reduced to some degree to increase velocity for the same discharge at the cost of a little resistance (so in effect a little smaller discharge)--this would push the water level in the vent that much higher.

I think what would end up happening is most of the pump's energy would go into pressurizing this open water column rather than moving water into the aquarium. If ultimately the water level in the vent was, say, two feet above the water level in the tank, the only flow into the tank would be that based on gravity for a certain sized outlet times the hydrostatic pressure (rho*g*2 ft).

I'm starting to hear that music they play in the Warner Brothers cartoons whenever there's a rube goldberg machine

Dan

 

[magikceph]

i think your right cuttlegirl, so far i have been asking way to many questions. im ust gonna take a trip to my LFS and maybe and aqaurium shops in San Francisco. thanks.