Hi Kim,
I finally got the time to assemble this, I'll e-mail you a PDF form also.
Let us know how it goes!
Glenn
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Quieting overflow pipe noise
Noise from return overflows in reef aquariums is a regular source of complaint from reef keepers. Richard Durso described a method for quieting standpipes in overflow boxes that has become very popular. (http://www.rl180reef.com)
The basic concept that makes the
Durso Standpipe work is that the water intake for the overflow is actually under the surface of the water itself. This feature both acts as a muffler for the sound and allows controlling of the flow of air required by the falling column through a small hole in the part of the pipe that is above water, which further reduces sound.
Many aquarium overflows don't use a standpipe in an overflow box, and instead are fitted to the back or side of an aquarium through a bulkhead fitting, as in Figure 1.
Figure 1 - Common overflow arrangement through tank back or side
There are several inexpensive ways to quiet this type of overflow arrangement that capitalize on the same principles that make the Durso Standpipe work. The easiest solution is shown in Figure 2.
Figure 2 - Simple method for quieting overflow
A PVC pipe cap is fastened to the top of the overflow strainer with a small stainless steel screw. Size the PVC cap so that there is ample room around the strainer so that the water flow in your system is not impeded. For this solution to work, two requirements must be met:
1. The bottom of the "bell chamber" created by the PVC pipe cap must extend below the surface of the water. It doesn't need to extend far into the water, but muffling the sound depends on a seal all the way around. Otherwise, you will get a loud gurgling noise under the edge of the chamber that does not extend below the water.
2. You must drill a small hole in the top of the chamber to allow the falling water column to take air in air that is required when the water column falls down the drain pipe. The hole size is not the same for all applications, and is a function of the amount of water flow you have. The Durso Standpipe suggests using a valve that is mounted in a hole in the top of the pipe, which will allow adjusting the size of the opening using the valve. However, once the correct size is determined it likely will never need to be changed, so I personally prefer to drill a small hole and then enlarge it until the proper size is reached.
The purpose of the hole is to prevent siphoning of the aquarium water through the sump drain. If you do not include the hole, or the hole is too small, the water in your tank will slowly fill to the top of the bell chamber as all the air inside the bell chamber is depleted. At that point, the conditions for siphoning are met, and the water in the aquarium will rapidly drain through the bell chamber and standpipe until the whole water level in the aquarium reaches the bottom of the bell chamber. This is usually accompanied by increasingly loud draining noises through your overflow plumbing. When the water level reaches the bottom of the chamber, the siphon is broken with a very loud sucking noise as air rushes under the edge of the bell chamber and into the drain plumbing. Then the whole fill/drain cycle starts over again. - very irritating!
If you choose to not use an air valve in this hole, then simply drill it out large enough to not allow siphoning of the water, and so that it does not create a lot of air whistle through the hole. I use a 1300
gph return pump in my setup; this arrangement required a ¼" hole.
One other point is that whether you use an air valve or not, the hole will likely experience salt creep over some time and will periodically need to be cleaned. It's obvious when this has happened; the fill/drain siphon cycle I described above will begin to occur if left too long.
The solution I described depends on the water level in the aquarium to be sufficiently high that a simple PVC pipe cap is long enough to extend from the top of your strainer into the surface of the water. If this is not the case, there are several other similar methods that can be used to accomplish the same end result. These are further described below. They are only a little more complicated to build than the first method I described, and will work equally well.
The next solution is to use a PVC pipe plug instead of a cap, and use a coupler or short piece of pipe to create the bell chamber around the strainer. This solution is shown in Figure 3. The primary advantage of this solution over the first method is that the pipe can be made any length to allow for a long reach from the top of the strainer into the water.
Figure 3 - Use of a pipe cap and coupler or short piece of pipe to create a bell chamber
Figure 4 shows the use of a pipe cap again, and shortening the strainer to allow a standard cap to reach the water when the water level is too low for a stock strainer. It, like the first solution, is very inexpensive and only slightly more complicated than if an unmodified strainer could be used. Its disadvantage is that some fabrication work is necessary to shorten the strainer and make an appropriate disk to glue to the top of it. Note also that if acrylic is use for the small disk, you must drill a pilot hole for the sheet metal screw, or drill and tap the disk to accept a S/S or nylon machine screw.
Figure 4 - Use of a standard PVC pipe cap and modified strainer
All three of the modifications I've shown have the disadvantage that they will limit the amount you can tilt the strainer/bell chamber assembly to adjust water level, if this was a feature of your particular overflow setup. If more than a few degrees off vertical are needed, the 2nd solution, using the plug and short piece of pipe, is probably best. This solution, shown in Figure 3, will allow you to adjust the length of the bell chamber pipe, or even cut it at an angle to match the water line, once the correct tilt for the strainer is known.
One other factor to consider is that these fittings do not by themselves allow for the natural removal of surface scum, as an overflow box will. There are several ways to fix this. By far the easiest method is to direct some water flow from your return pump past the assembly in such a way so that water turbulence will cause the surface scum to be stirred up near the intake. This will allow the scum to be sucked down the overflow naturally. It is possible to do this without breaking the seal formed by the submersion of the bottom of the bell chamber.
Figure 5 is the standpipe solution I currently use. Unlike the methods described above for returns fitted through a wall of the aquarium, I use fittings through the bottom of my tank because I wanted the tank flush against a wall. This would work just as well for fittings through the back or side of the tank, assuming they are positioned low enough to allow the whole final assembly to stand vertically at the water surface. I fashioned the 1-1/2" standpipe after a standard overflow box, and cut fingers in it to do the straining. I also used this to fine tune my water level, because after I made the vertical saw cuts in the stand pipe for the fingers, I only broke out about half of the fingers before I installed the pipe. Then I fired up the pumps, and fine-tuned the final water level by breaking out more finger material until the level dropped to where I wanted it.
I also made my most recent bell chamber entirely of clear acrylic. This allowed me to see the state of the strainer, and the thumbscrew makes for easy removal of the chamber for cleaning. The clear acrylic is readily available at stores that specialize in plastics, but the chamber shown here does require more fabrication work that the methods described above that use off-the-shelf PVC components.
Figure 5 - My current standpipe arrangement for 1300 gph water flow
These final touches were developed from experience. The first bell chamber I made was fabricated of black ABS, and was very securely fastened to the top of the standpipe. I had an unfortunate fish death, and the fish was small enough to get sucked up against the strainer under the bell chamber where I could not see, nor easily retrieve, the body. By the time I figured out what had happened, NH3/NH4 and NO2/3 were well on their way to bad, and the body was a decaying mess. I had to pull the whole standpipe out to clean it well. That one messy experience and I knew there had to be a better way; that's when I built this current standpipe. I have used this assembly since September 2000, with no problems.
Should anyone try these modifications, I'd sure like to know about your experience. I am beginning to put together a compilation of plumbing experiences and methods for designing aquarium plumbing to make life easier when setting up a new system
Glenn Pohly
glenn@firstworld.net
