peet Posted April 1, 2003 Report Share Posted April 1, 2003 Does anyone know what the formula is to calculate flowrate through a siphon. I want to use it to calculate pipe size needed for a DIY W/D filter. The formula would have to incorporate the head over the tank side. Sure you must know where I can get that from John Peet Quote Link to comment Share on other sites More sharing options...
Pies Posted April 1, 2003 Report Share Posted April 1, 2003 Heya Peet. Be very careful when building a wet/dry using a syphon system. It is VERY easy to have either the tank empty, the sump (wet/dry) overflow and flood and some other problems. I've been through MANY different ideas for wet/dry, and without the use of an overflow and gravity feed its dangerous. There are some syphone action hand on the back overflow systems available, this way the water levels in both remail the same so the syphon can't 'suck air' or empty the tank. As for the maths you are looking for I don't think you will find it. There are some formulas around but they change depending on things like, how much water pressure is above the 'suck' part of the syphon. How far down the syphon is in relation to the waterline of the tank. The with of the tube. Etc. I've got some links to gravity fed sump type designs if you are interested. They explain in some detail (prior problems) the ups and downs of using a syphon action filter over gravity fed/overflow systems. Good luck Pies Quote Link to comment Share on other sites More sharing options...
Warren Posted April 2, 2003 Report Share Posted April 2, 2003 Its relatively easy to calculate the pipe size. The best method is as Pies says, us a siphon overflow / gravity feed system to the sump. This is a box on the side of the aquarium with a water level similar to the tank. There is a U shaped siphon to keep the level in the box similar to the tank. The overflow comes out of the box and is gravity fed to the sump. Its a very standard setup us by many wet/dry systems when there is no pre-drilled hole in the main tank. The siphon pipe size is basically proportional to the difference in the water level between the tank and the box. The size of the pipe is basically a resistance to the flow with a little drag added from the sides of the pipe to help confuse things. A pressure drop is caused in the siphon pipe by a drop in the water level of the box. This cause flow. It is our good friend gravity that creates the pressure drop in the pipe. You probably don't really need to calculate the pipe exactly in reality. All it will tell you is that for a given height different between the water level in the box to the tank you'll need a certain diameter pipe. I used a 40mm inside diameter pipe on one of my tanks with a 5000L/hr pump. The level difference between the tank and box was 35mm. If I needed less difference I would have used a bigger pipe or multiple pipes the same size. Basically the less resistance in the pipe(s), the less pressure is required to get the flow, therefore the smaller the difference in water levels. If you really want to work out the pipe size I'll see if I can dig out the correct maths to help you out. I can tell you right now how to work out the pressure, but I'd have to look up how to work out the resistance and drag in the pipe. It will also depend on how many 90' bends in the pipe and the bend radius as well. pressure p = height (mm) x gravity (g 9.81m/s²) in N/mm² Once you know the pipes resistance and drag, flow = p*(r+d) where r is resistance and d is drag resistance in mm. This is just off the top of my head and really need a bit more work to make sure I've really got it. If you want me to get the real formula let me know as it could be a bit of work and I don't want to do it unnecessarily. Warren. Quote Link to comment Share on other sites More sharing options...
Shilo Posted April 2, 2003 Report Share Posted April 2, 2003 If unsure on pipe size (despite the maths which make my head spin) get the larger size then expected. I use 2X 13mm pipes from the 2 pumps (312ltr/hr each at tank level), the outlet pipe (overflow to sump) is 20mm with a reducer to stop any gurgling. The U shape syphon between the inner and outer containers of the overflow is 35mm (pvc sink u bend). With these dimensions I have no problems with any water overflowing. Use the size pipe that fits your pump as the first guide, double it for the outlet pipe then double this one for your syphon. Not exact science but allows for plenty of room for error. You can always reduce the flow with valves but you can't increase it without replumbing your system. See link below for an example system (needs updating) Quote Link to comment Share on other sites More sharing options...
Warren Posted April 3, 2003 Report Share Posted April 3, 2003 Well done Shilo, - exactly my point. Use overkill. The piework is cheap, so why spend hours calculating. Quote Link to comment Share on other sites More sharing options...
peet Posted April 3, 2003 Author Report Share Posted April 3, 2003 Hey guys, I been searchin and have found the maths for the pipe diameter of a siphon. Use v = (2gh)^0.5 in m/s where v = velocity of water at the siphon exit g = gravity = 9.81 m/s^2 h = the difference in height between the tank water level and the sump Now A = Q/v Where A = x-sectional area of pipe (m^2) Q = flowrate of return pump (m^3/s) NB must change from l/hr Now using A = (Pi)(D^2)/4 rearrange to find D Where D is the diameter (m) Very simple, so for a 1000 l/hr pump with a height of 1.4m between the tank level and sump needs a pipe of diamter +/- 9mm diameter. By the way warren, is the W/D filter being used on that HUGE (8ft) discus tank of yours? 5000 l/hr , how many WATT pump is that. Quote Link to comment Share on other sites More sharing options...
Warren Posted April 3, 2003 Report Share Posted April 3, 2003 Pump is 100W, 6000L/Hr at 0m head. I have 0.5m head + mechanical filter. Have measure how long to fill 100L drum. Total output based off measurement is about 4950L/Hr. Pump is Grundfos FP4 now known as the Oase 6000. I purchased mine for $300 8 years ago. After Oase bought the design off Grunfos, the price has tripled to $890 for the same pump, *$#!@rd's. Quote Link to comment Share on other sites More sharing options...
Interfecus Posted April 4, 2003 Report Share Posted April 4, 2003 Peet, all correct except for the last bit. Area = Pi * r^2 r=1/2 D Area = (Pi)((D/2)^2) Q=Av Q=(Pi)((D/2)^2) * ((2gh)^1/2) Quote Link to comment Share on other sites More sharing options...
Aqua Posted April 4, 2003 Report Share Posted April 4, 2003 I think I'm going to have to give up fish keeping if it involves math like that!!!! Quote Link to comment Share on other sites More sharing options...
peet Posted April 4, 2003 Author Report Share Posted April 4, 2003 Dont want to sound like a kook but Pi(r^2) is the same as Pi(D^2)/4 because if r = D/2 then r^2 = D^2/4 mmm well catch ya later Quote Link to comment Share on other sites More sharing options...
Shilo Posted April 5, 2003 Report Share Posted April 5, 2003 Yeap, my head is spinning !! :roll: Quote Link to comment Share on other sites More sharing options...
Caryl Posted April 5, 2003 Report Share Posted April 5, 2003 There's something to be said for pre-made stuff. You don't have to know or understand the math! :lol: Quote Link to comment Share on other sites More sharing options...
Ira Posted April 5, 2003 Report Share Posted April 5, 2003 I dunno, I find it pretty satisfying to use such basic math to figure out if I'm doing things right. Especially if it saves a few bucks. Quote Link to comment Share on other sites More sharing options...
Interfecus Posted April 5, 2003 Report Share Posted April 5, 2003 Sorry peet, it does work. Quote Link to comment Share on other sites More sharing options...
Warren Posted April 5, 2003 Report Share Posted April 5, 2003 Totally agree, why spend hundreds of dollars on gear you can make for under $20, especially if you can make it at least as reliable. Quote Link to comment Share on other sites More sharing options...
Caryl Posted April 5, 2003 Report Share Posted April 5, 2003 You can only make it if the 'basic' math makes sense, which it doesn't to the many. Quote Link to comment Share on other sites More sharing options...
Shilo Posted April 5, 2003 Report Share Posted April 5, 2003 On the contrary Cayrl, you can make what ever you want easily enough without complicated maths. Just think things through, doodle on that important piece of paper at work and research as much as possible. Of course if you want it to be "perfect" then get a phd in quantum physics, but a DIY filter system (or anything else) drawn up on a bit paper and which works as intended is just as good as one where the parameters are designed with mathematics. It probably would be better since the boundaries between the system working or not wouldn't be so fine and unlike a mathematical model, a level of caution would have been added. Don't be scared of DIY by "complications" since anything you make can be remade. Knowing when to stop fiddling with the contraption is the hard bit (my problem :oops: ) Quote Link to comment Share on other sites More sharing options...
Ira Posted April 5, 2003 Report Share Posted April 5, 2003 Nothing complicated about it, plug the numbers in and it's just 6-7th grade math after that. Quote Link to comment Share on other sites More sharing options...
Pegasus Posted April 5, 2003 Report Share Posted April 5, 2003 DIY starts as a glimmer of inspiration that comes to you when you see something that could obviously be made cheaper, or improved in some way. At times you use an existing concept... but look at it from a diiferent angle, and in a different light, so invariably you raid the junk pile or the house for that "certain" thing that "may" just do the job, or becomes the "base" for the project to get started. Again, at this point you are reluctant to "splash out" and spend funds on something that is just a dream at the initial stages, but as it comes together and might be showing results you may then decide to "improve" it slightly with a few bits from the local hardware shop. A scribble here and there, and a bit of thought, and before you know it you have a prototype... that may or may not need more work... but the personal achievement that you gained through all this is the only reward you need, for to see something working successfully that you have created is a great feeling... and really there is little need for complicated mathmatical formula's to produce the end product. Knowing that... Use v = (2gh)^0.5 in m/s where v = velocity of water at the siphon exit g = gravity = 9.81 m/s^2 h = the difference in height between the tank water level and the sump Now A = Q/v Where A = x-sectional area of pipe (m^2) Q = flowrate of return pump (m^3/s) NB must change from l/hr Now using A = (Pi)(D^2)/4 rearrange to find D Where D is the diameter (m) ... is great I suppose... if you feel that way inclined, but is not a consistant factor if you consider that this will "only" work on the new installation, and as time passes flows will reduce through internal restriction, or blockage from plants etc.. so the formula is probably feasanle on paper, but may have its faults in practice. Education or not... DIY can be had by us all... Think it... Dream it... Do it Happy Days, Bill (Pegasus) Quote Link to comment Share on other sites More sharing options...
Ira Posted April 5, 2003 Report Share Posted April 5, 2003 And that's why you use a safety factor and go with maybe an extra 25% flow for when things start getting gunked up. Quote Link to comment Share on other sites More sharing options...
peet Posted April 7, 2003 Author Report Share Posted April 7, 2003 You are absolutely right Pegasus, DIY is sooooooo rewarding. Ive sometimes over spent or "wasted' time on projects but Id much rather fiddle than let someone else have all the fun and get allthe money. I was not intending to try and complicate peoples lives, but as a an engineering graduate I find the maths behind nature captivating. In fact Im not even that fussed about keeping the fish themselves (but I do luv them), more interested in creating an ecosystem that functions in a completely unnatural environment (ie a glass tank) mmmmm hydraulic maths, can't wait till the next project!!!!!!!!! (what about a new background after reading that awsome polystyrene b-ground post) Peet Quote Link to comment Share on other sites More sharing options...
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