Periscope drain

Homer Allman · Aug 12, 2015

Ok i'm back with results, kind of. I rigged up the periscope drain on a 55 gallon trash can. I didn't take any time to glue any pipe or even have a bulkhead. I just drilled a hole. put my 2 inch pipe through and siliconed it. So there is some dripping around the bottom. I drilled the drain hole all the way in the bottom back of the can, just like I will in my tank. I filled the can with water from a hose. about 5 gallons a minute. The drain started draining and the water level remained consistent in the can. I turned the water off and the drain kept draining for about 7 minutes when the last trickle STOPPED.

The water level dropped maybe a half inch in the can to a predictable level. I will be able to dial this in to the exact level I want my tank, when I do a precise pipe fit on my tank. What I have created is a drain to refugium near the bottom of the tank that will not flood your refugium once the power goes out. For those who had doubts. I have it on video and will post that later tonight. It's 8.5 minutes long and I need to get it loaded.

I now feel very confident that I can put a drain in the back of the tank any height I want and it will not flood. I plan to do three of these on the rear of my tank.

Homer Allman · Aug 12, 2015

zesty · Aug 13, 2015

What exactly is the video showing? Just that you can hold water? What is the (approx) drain flow rate? I never saw a full drain on the video, just the trickle.

Is your refugium going to be below the bottom of your DT? Or is it going to be "near" the bottom of the tank? That's going to make a difference in how I'm picturing your setup.

I'm not doubting anything, just asking for clarification...

beaslbob · Aug 13, 2015

what the vid shows is the container only drains to the horizontal portion of pvc. So no need for anything inside the container then a bulkhead at the bottom.

at least I think that was the idea.

my .02

Homer Allman · Aug 13, 2015

Beaslbob is correct.

I think I may have miss worded when I said drain. It's really an overflow drain to the refugium. A few bulkheads and some strainers and I have a nice clean overflow setup. Some of the guys were worried about it syphoning into the refugium if the power went out. This is not the case. It will not flood your refugium. I like it.

My bulkheads will be here tomorrow and then the drilling begins. I will take pictures of them installed on my tank.

zesty · Aug 13, 2015

That was my misconception, I put the term overflow and drain as interchangeable and that is not the case here.

Let's see the pics!

Homer Allman · Aug 13, 2015

When I get the bulkheads tomorrow I will take pictures of the three overflow drains I plan to install. Since it worked so well on the trash can set up I will install them deep in the back wall of the tank. The tank is 30" deep and I will install them in at 20" deep. My theory is better water turnover by having the overflow deep like this instead of the standard top overflow.

TheEngineer · Aug 13, 2015

Your test is flawed. The setup does not match your planned implementation. If you want to truly test this, you need to run plumbing down the same distance as it will be on your final tank and the bottom of the drain needs to be in the same place as it will be for your sump and the water flow into the bucket needs to match your pump's flow rate. You haven't done any of that.

Additionally... Will it be suspended over the water in the sump? Will it be submerged in the water. I'm pretty confident you are running a strong risk of pulling a siphon on this.

I haven't done the calculations, but are you sure you can handle the flow rate you plan on putting in? My gut says no.

Homer Allman · Aug 13, 2015

I'm confident it will work. Nothing past the upper u turn will effect the water from draining out the bottom. How many gallons can three 2 inch drains handle, if they are running 3/4 full?

TheEngineer · Aug 13, 2015

You are absolutely 100% wrong. The pipe from one end to the other is a closed system. Where are you expecting the air to come in that replaces the volume of water that is travelling down the vertical section of pipe? (AKA how a siphon is broken)

Now you're making up numbers "3/4 full". You're so confident in this with absolutely no backup that it is actually a little annoying. Hence other people's reactions too.

I have a master's degree in mechanical engineering, so let's just assume I know what I'm talking about. If that's not good enough, do the math and prove me wrong. I did the math and was planning to post it, but your confident so I won't.

You're wrong, your plumbing won't work, you will flood your house.

TheEngineer · Aug 13, 2015

<Deep breath>... I changed my mind. This is about helping people in the hobby, even difficult ones.

Let's talk about this more...

Homer Allman · Aug 13, 2015

Ok man take it easy. It's only a hobby. Flashing around some degree does not impress me at all. Look it either works or it doesn't. You saw a small test video of a new overflow technique and you think you know everything i'm doing with my plumbing. Time will tell.

Windy · Aug 13, 2015

Why not do it then?

Homer Allman · Aug 13, 2015

I am going to when my bulkheads arrive tomorrow.

TheEngineer · Aug 13, 2015

So let's think through each section of the drain one at a time...

Drain to Top horizontal section:
The assumption is that the water level here will never increase above the height of the water's surface in the tank. That is correct if nothing else is attached to this section of pipe. We need to look at the next section to see if it has any forces that can act on this section.

Top horizontal section:
The thinking is that the water level in the top horizontal section of pipe will never go above the height of the water in the tank. This is correct if nothing else is connected to this other than the previous section. There is nothing there to pull a siphon out of the tank.

Vertical section to sump:
My guess is that you are thinking this section doesn't affect the system. This is where your test is flawed. Have you ever started a siphon by putting the tube in the water, covering the end, pulling the tube out with some water in it and letting go? The volume of water in the tube that you pulled out of the water in the siphon (thanks to gravity) falls to the bottom of the tube and since air can't fill in the space behind that falling water, more water is pulled into the tube. Now there is more to it than that, but that's the important part. The same concept is at work here in your vertical section. Let's assume it is running and the power dies. All of the water that is in the tube will fall and pull on the water behind it unless there is a way for air to come in and replace the volume.

Intersection of Vertical section and sump:
You haven't said what your plan is here. There are two ways you can have this: the pipe outlet is under the water, the pipe outlet is over the water. In the first case, you have no path for air to enter the pipe, a siphon will result. In the second case, there's a chance to pull air in, but it has to combat the the flow of water coming down.

So, what do you think about those statements? Do you disagree anywhere?

Homer Allman · Aug 13, 2015

If I need air. I will drill a hole.

TheEngineer · Aug 13, 2015

You can't just drill a hole, then you'll have a sprinkler instead of a drain. You'd need a riser with a cap on it and drill the hole in that. Now you have something stick up over your tank's lip. Something you said you don't want.

You also need to figure out if you can handle 8000gph of flow (I think that's what you said you wanted) through those drains running open instead of a siphon. Full siphon, 1x 2" drain is something like 12,000gph.

StikHedRon · Aug 13, 2015

Taggin along as I wanna see the end result. Did he just waste his money by messing up a 300 gal tank or was it successful?

Homer Allman · Aug 13, 2015

Want and have are two different things. The return pump will have to match the overflow capability, of course. I'm pretty sure they really do not make a 12,000 gph pump for our hobby, none that I've saw anyways. 3000 gph will be plenty on the return loop. Power heads will do the rest.

DaveMorris · Aug 13, 2015

I believe the assumption being made here is that the flow through each of the three installed 2" periscopes will be nowhere near enough to result in a full siphon in any possible scenario. I questioned this in the beginning of this thread. If the flow is slow enough that each of these pipes has only enough water flowing through them to trickle, then the trash can demo will hold true, assuming that the drain is above the water level in the sump. I don't like this because A) it will be very noisy and B) when the water level in the sump rises above the bottom of the drain pipe the risk of siphon becomes very real. If a hole is drilled in the top of the horizontal section of pipe, yes it will allow air in to help prevent siphon, but it will contribute to the noise in the system.

All that being said, the biggest issue I see here is the fact that you will not be skimming the surface. There is a reason why everybody in the world does an overflow this way. It is the most efficient way to remove the contaminants that cling to the air/water interface. You mentioned that you plan to have crazy flow in the tank so surface skimming won't be necessary. That is somewhat flawed logic. Will your tank become a disaster if you aren't surface skimming? No but it loses a lot of the efficiency that a surface skimming overflow provides.

You will also need to be able to get at the screens easily to clean them on a very regular basis. I would also plan to peel a fish or two off of them as well. I learned this the hard way with a closed loop intake. It doesn't take very much suction at all to keep a fish pinned to the screen, especially if it is sleeping and drifts in front of it.

Good luck and keep us posted.