irrigation water? wasn't sure where to post this hope I'm in the right place!

Hey folks,

So I'm trying to find information on syphon systems and how they work/don't work (in my case) . . .

Basically I've plunged my pipe into a rock pool about 75-100m above my house, and the pipe is about 400m long (to the river) comprising 1.5 inch down to 1 inch, then I've got 350m's of dripper hose split into 3 stations. I started the syphon by filling up the entire pipe with water and just opened a valve at the bottom of the steepest slope. It has been working fine for stop/start hand watering and other things but when I leave one of the dripper stations on for longer than let's say 4 hrs enough air travels back through the system to the top and stops the syphon, or at least that's what I think is happening.

My question is how can I stop this air getting in and traveling back up the system or is there a fitting I can install which removes the air or what is the solution? Just I can't keep climbing the waterfall every one or two weeks to re-fill the pipe especially coming into Winter it might not even be accessible. Failing any solution I guess I could move the point in which I re-fill the pipe to a safer spot. Could I put a tee at the top of the curve before it plunges into the pool and have it open to let the air expel or would the syphon not work in that case?

Let me know any suggestions.

Much love
Rich

Where is the air getting into the system?
An air valve at the highest point of the pipe system may be needed.
Look at 'design and 'construction of city water supply pipelines'.
If an air bubble is created in the high point, that fills the whole pipe, flow may stop, and air valve allows that air to evacuate the pipe.

In my opinion you need a gate at the top to stop the flow when the water level drops and the pipe starts sucking air.

An inexpensive bilge pump AND a bilge pump float valve (situated conveniently) will do, with the 'T' at the top to prevent passive siphoning.

John C Daley wrote:Where is the air getting into the system?
An air valve at the highest point of the pipe system may be needed.
Look at 'design and 'construction of city water supply pipelines'.
If an air bubble is created in the high point, that fills the whole pipe, flow may stop, and air valve allows that air to evacuate the pipe.

thanks buddy I've been away and just getting back to this now!

an air valve sounds like a plan so air getting into causing the flow to stop can escape near the top of the system. I could fit a 1.5 inch Tee and hopefully find a valve to screw into that.

Do you happen to know what this part might be called and have a picture of one?

Burl Smith wrote:In my opinion you need a gate at the top to stop the flow when the water level drops and the pipe starts sucking air.

An inexpensive bilge pump AND a bilge pump float valve (situated conveniently) will do, with the 'T' at the top to prevent passive siphoning.

As I was writing John's reply it clicked what your saying . . . lightbulb moment . . .

Could that be what's happening I'm actually draining the pool when I irrigate?? And the water level drops to below where my pipe is anchored (virtually the bottom)?? But the pool is being constantly refilled by the stream, surely I'm not draining it quicker with just a few dripper lines 🤔 Maybe though, because the times it seems to happen most (syphon stops flowing) is when I leave the drippers on for extended periods (or when I forget to turn them off). I guess the only way to know is go and watch the pool levels when I turn on the irrigation.

If that is the case can you fit a gate to the end of a 1.5 inch pipe or more specifically in between a 1.5 inch joiner and filter? It would ideally have to be some sort of mechanical gate/valve as I can't get power to this location without setting up an independent solar system and power station.

Maybe you should spend some time watching the system.
You may well be draining the pond, in which case you need to consider a method of stopping the flow after a set time.
It is possible to add a saddle to the pipe instead of a T fitting, they are more economical and will be threaded to accept a valve.
Ball vales are more reliable than gate valves.

You are getting air in some place.  Is it stopping when you are in a low flow mode or when you are running at max flow.  Sounds like max flow.  So most likely it is sucking down to within 4 or 5 inches of the top of your pipe at the head end, then creating a whirlpool vortex that sucks air from the surface.  A good siphon with lots of flow will eat a tiny amount of air steady state by mixing it with the downstream water and dragging the bubbles out the bottom end but it takes very little to disrupt this by getting too much air in, creating a bubble and stopping the flow.

Now they do sometimes put what amounts to a chamber on the top at the highest point that will trap some bubbles but its capacity is very limited.  Now if you have a lot of flow on the downhill side there can be a line running a ways down the hill inside the main pipe.  The main pipe does a mild constriction and the line runs just past it creating a vacuum that pulls air out of the chamber.  The chamber is often used for priming large systems.  Turn the valve off at the bottom end and suck air out of the chamber till the pipe is full.  Since the chamber is the highest point in the system that is where the air collects.  Seal the chamber off, open the valve slowly and the siphon is off and running even in really big pipes.

But sucking air at the inlet will disrupt the best siphons no matter what you use.  One thing I had minor luck with was a piece of window screen floated above my inlet pipe where I couldn't get it deep enough.  Put a flat board there and the vortex just craws along it till it can snake its way to the surface.  But the window screen sort of grinds the vortex up so it doesn't reach the edge.  Was only partially effective but seemed to help a little under the right conditions.  It is critical though that you do not pull too much water and expose your suction pipe.

Now guessing the discussion of an air valve there is either a suction port or and air admittance valve to prevent suction or cavitation damage while draining a big line.

put a check valve in the main line. also I found with drip irrigation a filter is useful to prevent any sand or dirt that may get in the line that might plug up the drip tape and emitters after a while

Regarding your issue,

Personally I can't stand siphon tubes for irrigation. I've been around farming all my life and have never been able to get those "BLEEPING" things to work.

My advice is to convert to a pump. Solar powered ones are out there and are very reasonable if power isn't already there. You drop your pump intact to your pool of water then pump it into your pipe.

But also find a neighbor that uses the same water source and see what they say. What's the worst that can happen? They would ask you to leave. But in my experience, neighbors help neighbors. They can show you how to get your system to deliver your water.

Call around to farm irrigation companies. They are the ones that would help you as you may likely go to them to buy your pieces you need. That or call your local County Extension Advisor. They would definitely help you out. Or go to your local farm store/Co-Op & ask them. Conservation District may help you out as well.

That's my 2 cents worth, hope it helps!

Hoppy