Siphon size for a given flow rate data wanted

BullwinkleII

I'm looking to create a chart for my blog showing siphon sizes matched to flow rates, and was wondering if anyone would be willing to share their flow rate and siphon size.

I'll make a chart and extrapolate(I think that's what I mean) the gaps so a new comer can get a bit of an idea of where to start when making their first siphon.

Obviously the chart would be available here as well.

So if you happen to KNOW (guesses will just throw off the data) your flow rate and siphon size, and feel generous, post it up.

I'll make up a few test siphons if I don't get any response, I'm just trying to save myself some work.

So even if you do nothing, I'll still post results.

I probably shouldn't have mentioned that

BullwinkleII

I have one that water comes in at 14 seconds per litre, with a 12mm (internal) standpipe, but the 12mm pipe is a short reduction pipe in the top 50mm of the standpipe.

I'm not sure what that would do to the flow. ie going from 12mm to 19mm

I dont think that's quality data.

So I'll ask for seconds per litre, or flow rate only from siphons that flow through a standpipe that doesn't vary in diameter.

[or do anything else wacky]

bunson

The flow rate is going to depend on more than just the standpipe diameter, length also plays a very important role in the computation,as does the number of twists and turns, elbows and 45s, P loops, S loops etc.

Standard gravity flows though pipe diameter 'x' of length 'y' with elbows and turns are available from nearly all manufacturers' websites and some "generic" models are available at many different engineering websites. That'd be the place to start IMHO.

BullwinkleII

The problem is, that wont tell me when the siphon will start and stop. I have no idea what percentage of gravity fed flow is the sweet spot for various pipe diameter.

And what you say is quite correct, the length and kinks etc would all have an effect.

But if I could collect some data, I think a graph would make it a bit more clear as to where to start. I'd just need more data than I can create by making siphons myself.

I'm just sick of answering "I have no idea" whenever I get asked "how big should my siphon be?", and I get asked that a lot.

I'd feel a lot better if I could show them a graph and tell them this is what 30 other people did.

slowRider

I have a 210 gph pump running thru 1/2 inch PVC with a 1 inch diameter stand pipe and 2 inch diameter bell. There is about a 14-15 inch drop from the top of the stand pipe before hitting a 90 degree, a 12 inch horizontal run that goes to a make-shift venturi, then the final drop of 4-5 inches to the tank, but I think the venturi essentially breaks the siphon so the last few inches of drop makes no difference.

My grow bed is not full of media yet, so I might have to reduce the pump volume to make it cut off properly. I was having issues with the siphon not breaking initially and discovered (by removing the cap to the bell) that my bell didn't have enough holes at the base to allow enough water to come in.

So, on top of all of the things that bunson brought up, there is also essentially a guarantee of flow restriction from the bell. With a low volume input this could help the siphon start. In my case, it prevented it from stopping without creating a serious restriction on the pumping volume.

A few resources...
http://www.ctahr.hawaii.edu/oc/freepubs/pdf/BIO-10.pdf
This is what I used to size my stand pipe and bell... works well, but it could have been luck.

http://www.engineeringtoolbox.com/pipe- ... _1734.html
We know that we have to fill the stand pipe with enough water to make a seal. A restriction will help with that in the form of a funnel at the top (Affnan-style) or a 90 degree somewhere in the middle... But since we know how much water is required to fill a pipe and we know the rate of speed it will move thru the pipe under the force of gravity (ignoring friction), we should know how much volume of water coming in is required for any given stand pipe diameter and length before restriction to start a siphon. Theoretically this should be static and someone smarter than me should be able to make a calculator for it and that would give us a minimum.

Next, we'd have to figure out the maximum volume of water to allow the siphon to break. Before the siphon takes effect, the water is working as separate units and accelerating from the top of the pipe to the bottom as a single droplet would. Once the siphon starts, all of the water would be acting as a single unit moving at the velocity it would at the end of the drop (minus friction). The diameter of both the stand pipe and the bell, and the ratio of stand pipe to bell diameters would affect friction a lot, but we should be able to establish a baseline for that and calculate the volume of water, then compensate with the baseline.

Or something like that... Too much caffeine and too little sleep makes me ramble apparently.

Paul

BullwinkleII

Mathematics is beyond my abilities according to MIT's beta test electronics course, and personal observation.

But I'm willing to _use_ any spread sheet you can come up with

Do you know the flow rate of the 210 gph pump at the point where it hits your growbed? I'm going to just use any data I can find and see what I can see. Regardless of the method of predicting, it would be nice to get a ball park pipe size to be able to give people.

Given that's its always a good idea to have a bit of unused water flow when you are calibrating a new siphon, it should be easy enough to give people a rough idea. ie "anything within these dots on this graph should at least be able to be coaxed into working"

I'm guessing the points on the graph will be closer than I think.*

*I suspect that's the first use of a logical Anti-Tautology on a forum.

slowRider

I measured the output as 16 oz every 6 seconds... so that should be a gallon every 48 seconds. If my math is right, that should be 75 gph, which is WAY below the stated max of the pump, but I suppose the 210 gph is at the pump outlet and doesn't take rise and friction into account... I'm glad I didn't go with a cheaper pump!

slowRider

Another piece of the puzzle...
http://www.irrigation.org/uploadedFiles ... Charts.pdf

grownathome

I can contribute some flow rate knowledge regarding a test Hubby and I performed last weekend. Hubby built an Affnan siphon in a bucket to prove to ourselves that it works. It worked first time! Yay!! We are also trying to understand what factors determine the rate of inflow required to trigger the siphon though. The siphon we built in our 9.5l bucket(no media) required 600l per hour fill rate in order to trigger the siphon action which seems excessive for the small system I am building - my grow bed will be 150l. We used a 20mm stand pipe with a 40mm reducer on top and 90mm bell. Would a smaller bell reduce the flow required to trigger the siphon? or would a restriction in pipe size below the grow bed be better? Or are there other tricks to make the siphon trigger at a lower flow rate?

BullwinkleII

Thanks for the data.

The best bet would be a restriction in the standpipe.

Lots of pipes fit snugly inside the next size up or down, I've used a combination of clear flexible tubing, black poly pipe, and PVC in the past to make reducers.
I'm not sure that a smaller bell would do a lot, because there is a minimum amount of water that will trigger a siphon of a given diameter. A smaller bell might only restrict the flow.

I run a siphon with a reducer in the top 2 inches of the standpipe, and that seems to work well. I've also had success adding a reducer to the botom, and also sometimes just an elbow joint will do the trick, but I always prefer to keep it simple and have a straight drop if I can. I suspect the more bends and tricks you employ, the more likely that the thing is only working because of a particular set of chaos creating the seal to trigger the siphon. I prefer to keep it simple, and once I have a roughly correct size standpipe, adjust only the water flow to get it sitting in that spot where it both triggers and stops in a fairly decisive way.

I ran a standpipe of 12mm in diameter, and a pump adding 72 lph to the grow bed. (my first blue barrel system with the siphon dropping straight down to the fish tank)

water flow needs to be enough that it forms a seal, and allows the fall of the water in the siphon to generate the required suction. If the flow is too little, it will run down the side of the standpipe and never trigger. If it's too great, it will not stop.

grownathome

Thanks Bullwinkle that all sounds like sensible advice. We will tinker and see what happens.

SnowT

Hey bull there are a few table on the web that give the flow rates dependent on pipe size..

I'll try hunting down the table.. All figures are related to gravity flow aswell.

Juergen

Charlie

This thread has got some really good info Bull. Definately worth a read for most people.

viewtopic.php?f=1&t=6544&hilit=rate

BullwinkleII

Charlie, I'm still reading that thread, but I'm not sure that the rise rate is relevant. I used to think it was, and I think I talked about it in my system thread, but I'm no longer convinced.

As soon as the siphon starts a small flow, the flow rate becomes the only relevant thing, because there is no longer a rise rate. The rise stops before the siphon triggers.

I think

BullwinkleII

Thanks SnowT

I'm not sure how to translate those types of figures, and take into account the siphon trigger. If you have any input on that please let me know. Is it just a case of matching a pipe to the flow rate based on looking it up on the chart? I'm guessing the fact that it triggers before it's full will have an impact, but perhaps we can draw some conclusion by plotting some real world examples next to the predictions.

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