What does the hole in the top of a Durso Standpipe Do? - The Planted Tank Forum
 
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post #1 of 9 (permalink) Old 06-13-2006, 10:54 PM Thread Starter
jgc
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What does the hole in the top of a Durso Standpipe Do?

Ok, I give. I am thinking about a diy hob overflow. I have seen some excelent threads on them, and have one nagging question. Durso Standpipes have a hole on the top. Why? w/o this hole, there would be an airlock in the drop tube. Is this a bad thing? Is the hole for tuning? Is it to prevent the airlock and lower the drop noise? Is it to start a syphon?

I am planning this for a nano sump, drop will be less than 8". While I can include the T, I just want to know why I should.

58 gallon oceanic, Kessel 360 tun sun, pressurized co2, eheim pimp #179 - 2217 and diffuser
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post #2 of 9 (permalink) Old 06-13-2006, 11:42 PM
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Quote:
Originally Posted by jgc
Is the hole for tuning? Is it to prevent the airlock and lower the drop noise?
Yep. Start with a very small hole and you can increase the size to get better flow rates and/or muffle noise.
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post #3 of 9 (permalink) Old 06-14-2006, 12:02 AM
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Without the hole, water in the standpipe goes up and down to allow air in. That along with the overflow box never filling is what makes the dreaded noises. The hole in the top is to allows air in to stabilize the siphon. Any noise the standpipe makes is drowned out because the standpipe inlet is kept below the water line. Additionally, it is important to use larger pipe on some size tanks to get the siphon. More information is available on Richard Durso's website....DC
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post #4 of 9 (permalink) Old 06-14-2006, 12:26 AM Thread Starter
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I think part of my confusion is the realitive flow difference between what I imagine and what reefers deal with. Durso's sight said the hole is to prevent a full syphon from forming on the down tube. This would be a disaster with the pvc overflow I am planning, and having a hole there might be good insurance. This is just insurance, as I am pretty sure a full syphon will not emerge given the meger flow that will be going through it.

58 gallon oceanic, Kessel 360 tun sun, pressurized co2, eheim pimp #179 - 2217 and diffuser
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post #5 of 9 (permalink) Old 06-14-2006, 01:00 AM
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The best way to see how it works and understand the function of the hole is to install the standpipe with the cap off. Look down into the overflow box and watch the standpipe and box drain/fill, put your hand over the hole and watch the flow. When drilling the hole, increase the size very little and let it run for a while. Theoretically, you want a pefect siphon, I do not think it is possible though, you will always get air traveling into the sump. I do not know what kind of set up you are planning, and what you are referring to as insurance, a standpipe will move water if it is underwater. If you are not using an internal overflow box, consider using a stockman standpipe....DC

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Quote:
Originally Posted by jgc
I think part of my confusion is the realitive flow difference between what I imagine and what reefers deal with. Durso's sight said the hole is to prevent a full syphon from forming on the down tube. This would be a disaster with the pvc overflow I am planning, and having a hole there might be good insurance. This is just insurance, as I am pretty sure a full syphon will not emerge given the meger flow that will be going through it.
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post #6 of 9 (permalink) Old 06-14-2006, 01:04 AM
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jgc:

It sounds like you should just start out with a standpipe (vertical, open top). If that is too noisy then try the durso. If a full siphon would be "a disaster with the pvc overflow" something sounds wrong to begin with and the siphon in the overflow might break during a power outage...

So when the hole is covered on my durso, the first thing that happens is that the water level rises until the spillage displaces enough air that a full siphon forms followed by a rapid drop in the water level until it is even with the bottom of the durso. This breaks the siphon with a series of gulping sounds. The water level then rises etc. Without the hole, the nearest household example is the toilet in both noise and action.

Quote:
Originally Posted by jgc
I think part of my confusion is the realitive flow difference between what I imagine and what reefers deal with. Durso's sight said the hole is to prevent a full syphon from forming on the down tube. This would be a disaster with the pvc overflow I am planning, and having a hole there might be good insurance. This is just insurance, as I am pretty sure a full syphon will not emerge given the meger flow that will be going through it.

Moved to Tucson.
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post #7 of 9 (permalink) Old 06-14-2006, 01:04 PM
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I'm pretty sure that the main reason Mr. Durso came up with his design was to eliminate noise from the system by keeping the overflow section full and muffling the sound of the water in the pvc.

jgc: on the other thread where you posted (the constant level siphon) the drilled cap on the open T is to act as a muffler. When I have people over I take the caps off of the overflows, let them hear the noise, then I put the caps back so they can hear the difference.

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post #8 of 9 (permalink) Old 06-14-2006, 02:25 PM Thread Starter
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Bingo - planning a constant level siphon based on Diy pvc overflow retrofit?. It is essentially a siphon to an external overflow box (consisting of 3 U's - siphon, overflow box, and overflow tube). Like any external overflow box, breaking the siphon from the aquarium will result in the aquarium overflowing as the sump drains it's entire contents into the aquarium.

The one I am planning will be nano sized, with disproportionately large tubing compared to flow rate - I am almost certain the flow will be insufficient to blow out the bubble of air in the overflow tube (which ultimately would result in breaking the siphon to the tank).

That said, while I am pretty sure the hole would not be necessary to prevent "burping", I might put one in to insure it can not happen. To be honest, I might just use a "L" fitting rather than a "T", but drill a small hole into it.

Thanks for the insight into the black.

58 gallon oceanic, Kessel 360 tun sun, pressurized co2, eheim pimp #179 - 2217 and diffuser
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post #9 of 9 (permalink) Old 06-17-2006, 02:06 PM
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On my 180 gal tank it came with the Megaflow Overflows installed. The stand pipes are basically the Durso Stanpipes with adjustable height. I too didn't completely understand the concept until I saw it work. To simulate what it was like without the hole at the top, I raised the pipe until the hole was pressed against the glass top of the tank which basically plugged it. With the pumps in the sump running the top tank filled with water until it reached the top overflow column. The chamber inside the overflow column then began to fill with water. As the water inside the column reached the standpipe entrance it began to flow down the standpipe, but at a slow rate. The water level in the overflow column continued to rise because water was flowing in faster than flowing out until it reached a level where no more air could be sucked into the stanpipes intake. At which point a complete syphon was created in the stand pipe and water began to flow out of the column much faster than it was flowing in and as a result the waterlevel in the column began to lower, it continued to lower until a little past the point to where the standpipe could suck in air. Sucking in air would break the syphon and slow the water flow rate and the water level would begin to rise again. Every time the syphon was broken the standpipe made loud burping noises.

Now slightly lowering the height of the standpipe to where the hole at the top was nolonger blocked allowed a small continous small stream of air to enter the pipe. This allows the syphon effect to reach a balance to where a complete syphon is never created but the flow rate is as fast as it can go without a complete syphon. This keeps the water level in the overflow column at a constant level and eliminates the burping noises.

Basically too large or too small of a hole and you get the noise along with a water level that varies in the chamber containing the standpipe.
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