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siphon discharge failure

siphon discharge failure

siphon discharge failure


I'm working with a float siphon to discharge water into a wetland. the siphon is reaching its drawback height of 0.44m but is not discharging as per design (11 times) its only discharging once per day. I'm wondering what the problem could be. A float siphon is a type of siphon that works on buoyancy principle, when water incoming into the siphon chamber reaches a certain height 0.44m (drawback height)the water exerts a force on the siphon and forces it fall back thereby drawing water in. for a further description of how the siphon works please view the attached file.
Average discharge Ǭ = 0.0351m3/s
Pipe diameter = 110mm
Water viscosity 1*10-3 kg/ms
Density of water = 1*103 kg/m3
Roughness height e for PVC = 0.0015mm
Acceleration due to gravity =9.81m/s2
Area of the siphon chamber 2.6m by 3m

RE: siphon discharge failure

I'm wondering how you expect anyone to provide any input without giving them any relevant information.


a diagram would help to explain you system and also how it was intended to work versu how it works now.

what do you mean by "float syphon"
what do you mean by "drawback height"
Whhat is flow / tank or pond size?

Maybe there is only 1 tenth of the water coming in?

We have abut 1% of the information here to offer any salient advice.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: siphon discharge failure

Thank you LittleInch for response and advice I have added more information

RE: siphon discharge failure

Nothing attached.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: siphon discharge failure

Not knowing the details of your siphon, one would expect that there is not enough elevation between the water levels.

RE: siphon discharge failure


Thank you bimr for response

I am sorry the link failed to attach but below is the link address


I don't think its the problem in the difference in elevation otherwise it would not discharge at all, it does discharge once but not 11 times. Another thing I noted was it reaches its discharge height of 0.44m and maintains that height for about 20-24 hours without any discharge whilst maintaining that height (I could not find any leaks in the siphon chamber) irregardless of the fact that water is still incoming into the siphon chamber, I was expecting the water level to rise but it remains constant.

RE: siphon discharge failure

The attached file is an mp3 track? Won't load or play and I want a diagram / video not someone talking to understand what you mean.

Can't you sketch it and scan it it?

Are you referring to basically an inverted U tube? does the water simply dribble out?

If you don't have enough flow going round the high point it won't start to "syphon", but simply act as an overflow and dribble water out of the end pipe.

what is the end point? Below a water level or the open air?

what is the flow rate into the pond?
Have you tried a smaller pipe?

Perhaps you need something like this? http://chestofbooks.com/home-improvement/construct...

or this ( go down to automatic cistern) Are you missing the projection? http://www.users.waitrose.com/~ttagrevatt/vlav/wor...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: siphon discharge failure

Thank you all for responses

I have tried again to upload it Im not sure if it worked out well, In case it hasn't the link to the you tube video is https://www.youtube.com/watch?v=mxrBqMxbbS4

the float siphons works by buoyancy principle

when water reaches a certain height, it acquires a weight and when this weight is higher than the weight of the siphon, the siphon sinks into the water there by drawing in water through its pipes thus distributing it.

RE: siphon discharge failure

The attached PDF doesn't have any relevant information.

The YT video is not easy to see how the float is de-activated.

This needs a proeper engineering drawing and sketchest to show what should be happening.

One thing though - If the uinti is the same as in the vide it is NOT a syphon, it's simply an simple auto actuating float valve.

I would have thoguth you could do something much easier with a proper float valve, but the key is in that section at the end where the float sinks.

I suspect the setting isn't working properly and the incoming flow is dribbling down the outlet - have you checked? - without getting enough flow to activate the mechanism.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: siphon discharge failure

Thank you for response , will try and get a proper engineering diagram, currently I'm looking for any leaks towards the outlet, and do not seem to find any

RE: siphon discharge failure

Have you tried the bell siphon? It is simple and more reliable than what you are doing.



There are important rules of thumb with siphons:

1. This relationship of standpipe to bell pipe height is important in ensuring that the volume of air resident in the top of the bell pipe is sufficient to start the siphon.

2. Some restriction is needed in the outlet to slow down the flow.

RE: siphon discharge failure

Why not contact Flout? Is it not their system?

Sorry, the company is Rissy Plastics.


RE: siphon discharge failure

hydtools, yes it's the system I have, thank you for the idea. will do that

RE: siphon discharge failure

bimr, currently the treatment system is using a float siphon so rather than replacing it with a bell one the company wants to minimum purchasing costs and just fix whatever is wrong with the float one

RE: siphon discharge failure

If there is water coming into your tank, but the level in the tank does not rise, then it can only mean that there is a leak somewhere. If there is no water coming out of the tank itself then check if there is water coming out of the outlet (feeding the plants) - this will mean that there is a leak where your float system is attached to the outlet (or there is a leak in the float system itself). With such a simple system there isn't much room for problems to hide!

Katmar Software - AioFlo Pipe Hydraulics

"An undefined problem has an infinite number of solutions"

RE: siphon discharge failure

Katmar, thank you I will check for the leak on the outlet pipes feeding the plants, my question still is if there is a leak somewhere how come the siphon still manages to discharge even once, or twice or could be because of the increase in incoming flow rate, is so i have the second graph that shows that even though incoming flow rate increased and the height difference had been reached still the siphon did not discharge. If it is because of the contribution of incoming flow rate how come the height in the siphon chamber does not drop irregardless of a drop in incoming flow rate. see attached document. Please note a drop in height signifies a discharge

RE: siphon discharge failure


Like I've been asking for since the start, can you simply draw on a sheet of paper the cross section of your tank and list everything that is there - a photo or three would help as well.

I assume your flow figure in incorrect (0.8 m3/second?) and the LHS numbers are actually the depth in metres

Something seems to happen after a "flush". The level beforehand is generally a little higher than after.

I can only summise that at the water height you're at, the outlet flow / leak is being generally matched by incoming flow. Height does go up as flow increases, perhaps just enough to activiate this system, but otherwise just not quite high enough.

I don't know how you adjust the operating height, but why not try lowering it to say 0.400 and see what happens

Turn off the incoming flow and see what happens - if there is a leak then the level will go down - find the leak.

Is it going down an overflow or vent pipe?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: siphon discharge failure

If the system is not discharging, the float box is not sinking. Maybe the box ballast weight is not sufficient to ensure that the box sinks when the water reaches draw down height.


RE: siphon discharge failure

hydtools, we added a few weights to help it sink , maybe not enough?

RE: siphon discharge failure

What's going on with the "vents / overflows"?

One appears to have cloth stuffed in it (the one on the left / furthest away and the one on the right in vertical view looks like it has a hole drilled in it below the water line and is busy jetting in water?? Looks like the rather pitiful amount of water going into it is more than catered for by the leakage down these two pipes.

Unless all the chambers are interconnected it would appear as if only two of the chambers initially flood, hence there might not be enough loss of buoyancy to sink the entire unit.

The angle of the pipes doesn't look enough to me. From other diagrams and a bit of thinking, the angle would seem to have to be quite high ( 50-60 degrees from horizontal) otherwise the end box will float higher and higher. I suspect someone has tried to "adjust" it by those strange cut outs on two of the boxes.

The whole thing is slightly lopsided as well which doesn't help.

Why don't you just create a frame top stop it floating beyond a certain level? or add a clump weight and length of rope / wire to do the same thing? and sort out what ever is happening with the vent pipes.

PS - It would have saved everyone a LOT of time if you'd just attached the photos in the first place....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: siphon discharge failure

The problem seems to be that the design you have is for a dosing siphon. The design of a dosing siphon flushes out the entire tank:


I am assuming that you want a siphon that works on/off but does not flush huge volumes. That is why the bell siphon was suggested.


The bell siphon is relatively inexpensive. I don't think you will ever be able to adapt the dosing siphon to work in the manner proposed.

The only flow meter that will work for an application like this is an open channel type flow meter.

RE: siphon discharge failure

Maybe that the float boxes are rising too high and flow is going out the vents before the float boxes gather enough water to sink. The discharge will then be no more than the inflow.


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