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       A Completely Silent Overflow - Is It Possible?

Reefkeepers have long accepted the fact that, above a certain size, a reef aquarium should utilize a sump. Water travels from the display tank (DT) to the sump, where its filtered/skimmed, poked, prodded, and generally beaten into submission. The logical place for the sump is under the display tank. Because surface skimming is important to our quest to remove as much dissolved protein from the system as possible, standard procedure is to let the DT's protein laden surface water flow over a weir and into a box or compartment. From there it travels, in free fall, through a standpipe to the sump (this is where the noise normally starts) and is then moved back to the DT by the return pump.

One of the very few negative aspects of keeping a reef aquarium is the noise. There are noisy pumps, both water and air - but the noise they make is usually a steady low hum that tends to loose itself in the background. You learn to get used to it, if need be. Fans, chillers, and the like, also contribute to the noise of a reef tank, but they too produce steady, not so annoying  sounds. It's the overflows that are bothersome. That splashing, gurgling sound that you just can't ignore. I'm sure more than one aquarist has given up and left the hobby because of a loud overflow.

There have been many attempts over the years to come up with a solution to the problem. Some have come very close. There are the Stockman Standpipe and the Durso Standpipe. Both are valuable assets to the hobby, but often don't provide really silent service. The Hofer Gurgle Buster gets a little closer to the desired lack of noise - only my opinion, of course. As a matter of fact, I use the Hofer for both my refugium and my frag tank.

The real deal though, when it comes to silent overflows, assuming your overflow box is large enough to handle it, is what I call the BeanAnimal/Herbie Overflow. Three or four years ago Herbie (his UserId on Reef Central) started a thread where he described an overflow utilizing two drain pipes. A year or two later, BeanAnimal (yes, his UserId on Reef Central) made some improvements to the design.

There is a prerequisite to using this design - let's call it the SASO (for silent and safe overflow). The overflow box must be large enough to hold three drain pipes, each of which must be dimensioned correctly for the needs of the system.

A little about how it works

First, for illustration purposes, here is a pic of my SASO: 

(Note that all the pics on this page were taken when the system was running during a function test and the return pump was set at around 1/5 of its capacity. The result is a water level in the overflow box that is approx. 1" lower than it should be. I usually keep the overflow water level at the middle of the "T" on the full siphon standpipe.)

Overflow closeup

Please notice a couple of things in the pic:

  •  the standpipe in the center is what we will call the "full syphon standpipe". Note, that there is a ball valve on the pipe. The top of the pipe is sealed with a cap so that no air can enter.

  • we'll call the pipe on the right the "open channel standpipe". It has no valve and (though you can't see it - its behind the pipe), it has a 1/4" flexible tube sealed into the top of the pipe - by sealed I mean airtight. The tube is bent over and down so that it's open end is approx. 1/4" above the water level in the overflow box. It is fixed in that position and cannot move.

  • water enters both pipes from below the water level. This is critical for the full syphon pipe so that no air can enter. Any air in the pipe and a syphon won't be created. Air can enter the open channel pipe through the 1/4" tube, but we'll discuss that later.

  •  the middle of the horizontal portion of the "T", on the full siphon pipe, is approximately at the overflow box water level. The open channel pipe is placed about 1/4" to 1/2" higher. This difference in the height between the two pipes will ensure that the full siphon pipe gets going before the open channel pipe kicks in.

  • disregard the leftmost pipe for now.

Water flowing down a pipe tends to flow along the sides of the pipe. This leaves an unbroken column of air in the middle of the pipe. As long as the volume of water never reaches the point where the column becomes unbroken, the overflow will be silent. Standpipes only start making noise when the volume of water introduced reaches a point that air is trapped - the flow starts to become turbulent - it's then that the splashing and gurgling sounds start. Unfortunately, the flow we need in our systems is always more than enough to make noise.

There is one more way for a standpipe to be totally silent, and that's when it is working under a full siphon - no air means no noise! That brings us to the SASO. The principal is kinda simple, but aren't most good ideas? If I force a standpipe to run under full syphon by employing a valve that allows adjustment to a flow just under the capacity of the return pump, that standpipe will be silent. Problem is, a flow which is less than the return pump is producing will cause the water level, in the overflow box, to rise - and that's bad. After a while a volume of water equal to what was in the sump will be on the floor...

We need to do something about that little bit of water that, due to our valve adjustment, the full syphon standpipe is not able to handle. So let's add another stand pipe. What happens then? If we adjust the valve on the full syphon standpipe just right, we can keep the flow reaching the second standpipe to a minimum. In fact, we can keep it so low that all the water traveling down the pipe will adhere to the sides of the pipe. And as we discussed earlier, that leaves an unbroken column of air in the pipe. And that means a silent standpipe! Under ideal conditions, with correct adjustment of the valve on the full syphon pipe, the two standpipes will maintain the flow between the sump and the display tank in complete silence. Problem is, we all learn very quickly, there is no such thing as continuing ideal conditions in this hobby.

From the safety aspect, what we have to avoid at all cost, is the situation where, for whatever reason, the two standpipes cannot handle the volume of water entering the overflow box. Let's take a look at what would happen, if this should occur. First thing will be a rise in the water level in the overflow box. As soon as the water has risen to a point where it reaches, and covers, the open end of the tubing attached to the open channel pipe, air will no longer be able to enter the pipe. That creates, in effect, another full syphon standpipe. A drainpipe working under a syphon can handle many times the volume of water than a pipe that allows air to enter.

Assuming the diameter of the standpipes has been dimensioned correctly, that is based on the amount of flow required (I use 1-1/2" pipes on my system), the design with the open channel/full syphon pipes will allow the overflow to handle just about anything you can throw at it.

Now, notice the standpipe at the left of the pic, above. That's the failsafe pipe. It's opening is straight up and above the normal water level in the overflow box. Should some kind of catastrophic event take place that causes the water level in the overflow box to rise high enough, the failsafe pipe will begin draining water from the box. At that point, the overflow has three drain pipes in action! I, personally, can't imagine a scenario where this could happen.

A tour of the overflow on the Glass Reef

Here is a pic of the entire overflow, top to bottom. You can see the three overflow standpipes we've been discussing. The two other pipes, to the far left, are the return pipes that carry water back to the display tank after it has been filtered, skimmed, etc. in the sump.

Overflow closeup

This is a close up of the full syphon standpipe. You can see two things of importance here:

  1. the bulkheads are Schedule 80. These happen to be made by Hayward - the best, IMHO. Schedule 40 bulkheads don't belong in a system of this size, again just my opinion.

  2.  the ball valve is a quality True Union valve. When it comes to plumbing an overflow, at least for a medium large to large reef tank, don't skimp on the fittings. One note here, if I had to do it over again I would probably use a gate valve instead of a ball valve for this application. A gate valve allows for very fine adjustments. The ball valve hasn't really been a problem, but a gate valve would be nice.

    In the pic, notice the water disturbance at the surface, near the full siphon standpipe. It illustrates the large amount of water (2000+ gph) being sucked through the pipe!

Full syphon standpipe

Here's a close up of the lower portion of the standpipes. Notice that the they have unions to allow them to be removed for cleaning, etc. It's a good idea to place unions wherever a part of the plumbing may need to be worked on.

Lower standpipes closeup

Below, the full syphon and open channel standpipes can be seen as they enter the sump and deliver their water to a filter sock. That reminds me - an important point - the lower ends of the standpipes must end about 1" below the sump's water level. If they are not, the whole silent thing disappears.

Full syphon standpipe

A little about overflow boxes

An overflow box has two main reasons for existing:

  1. the use of an overflow in conjunction with a sump and water return pump assures that the water level in the display tank will always be maintained at a constant level - that level being the top of the weir in overflow box. Inherent in the design of a display tank/overflow/sump system is the fact that, it's the water level in the sump that will vary, due to evaporation, water being added to the system, or whatever. The water level in the DT always remains the same.

  2. a correctly designed and dimensioned overflow box will be very efficient at skimming the water surface in the DT. Surface skimming has a number of advantages. Gas exchange is enhanced, dissolved organics tend to rise to the water's surface and skimming moves them to the sump where they can be filtered out, the scum that collects on the surface is removed and the resultant clean surface allows more light to pass to the corals in the tank.

Overflow boxes can have a number of shapes and sizes. The kind of overflow box you have depends mostly of the tank itself. That said, if your tank is, let's say, 150 gallons or larger and you have the room, I would strongly recommend that you consider an external coast-to-coast (all the way across the back of the tank) box. Here is a pic of mine:

Full syphon standpipe

Let's discuss weirs, for a moment.

For most of the time I've kept reef tanks, weirs, like the overflow boxes they were attached to, came in many sizes, but they always had the same basic shape. They looked like a comb. The theory was that the "teeth" would serve to prevent any inhabitants of the tank from being accidentally swept into the overflow. And this was indeed the case - toothed weirs do a good job of keeping animals in the tank. The problem is, they don't promote the very best surface skimming. And, as has already been mentioned, surface skimming is important!

If you've ever watched a toothed weir at work, you've seen that the teeth cause the water to "back up" in front of the weir. The result is a water level that can be up to 5/8" higher than the weir, itself. That means that water, other than surface water, is reaching the sump. The solution to the problems encountered with toothed weirs is a smooth one - simple.

You can see the weir on my tank, in the pic below. It is the bottom part of the long narrow rectangle on the right, about a quarter of the way down:

Full syphon standpipe

Notice that the water flowing over the weir is very laminar. No splashing, very controlled - silent. Another  positive aspect of smooth weirs.

Now that I've told you toothed weirs are bad, I need to temper that a little. An overflow in a small tank, let's say 75 gallons or less, doesn't really benefit that much from a smooth weir. The volume of water being moved just isn't that large. I used tooth weirs in my frag tank and refugium, for instance. They are fine for those types of applications.

Here are a couple of close ups showing detail:

Return pipes

This one shows the 1/4" tubing for the air inlet on the open channel standpipe. It's not visible in the pic, but the tubing ends about a 1/4" above the normal water level in the overflow box. Should, for whatever reason, the water level in the box rise, the open end of the tube becomes covered with water, which shuts off any air access to the standpipe. This causes the normally open channel standpipe to become a full syphon standpipe. At this point the volume of water that the pipe can handle rises. More water flows down the pipe, which causes the water level in the overflow box to sink. As soon as the water level falls below the end of the 1/4" tubing, air can enter the pipe and it reverts back to its open channel status. In this way the overflow design automatically adjusts itself to changing conditions.

Return pipes

And a couple more pics of the overflow from different angles:

Overflow from the top

Full syphon standpipe



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