Airlock in low psi irrigation systems
My irrigation system is simple – I pump water to a high placed tank and then allow it to run down to the plants or trees which have to be watered. Occasionally, there is a problem – a connection has come undone and the water spews out before reaching its destination (easily diagnosed and easily fixed); or the connections are intact but the water does not emerge from where it should. This is due to a blockage which could be debris, such as algae, or an airlock. If the problem is debris, then its location must be determined and the material ejected. Fairly quickly achieved for if there are 8 bubbler heads and no water emerges from the last four in the line then the blockage is between bubbler three and four.
An airlock is another problem and it occurs usually because of poor system design. The problem occurs because there is an air bubble in the pipe between the container tank and the discharge point.
Thus water from storage tank A to outlet B is held up or slowed down by an airlock at C.
Possible remedies for an airlock
If the pipe from A to B is continuously downsloping there will not be an airlock. So one remedy could be to eliminate the upward slope at C. Another remedy could be to bleed out the air at C either manually each time the airlock forms or with an automatic device, or with a small hole at the highest point in C which would allow first the air and then the water to escape, but this wastes water. With my gravity feed systems all the water at A drains out through the pipes, so each time I began a new watering cycle an airlock will form, which makes manual bleeding tedious. Initially I thought that a bigger diameter pipe from A to B would solve the problem and I increased the diameter from 1” to 1.25” but this did not help and may have made it worse – the bigger the pipe diameter the bigger the airlock (in fact I have seen it suggested that the diameter of the pipe at C should be reduced to minimize the problem).
My airlock solution
Now if the pressure of the water (psi) at C is increased, the higher pressure can eject the bubble out the airlock. So my eventual solution was to: i) raise the height of A by placing it on cinder blocks; ii) straighten out the pipe at C as much as possible; and, iii) if an upward tick is unavoidable make it occur as close to B as possible. The closer C is to A the bigger the problem since the height of the water above C is reduced and therefore there is less pressure. So if air bubbles are a problem begin the inspection first with the piping closest to A. If B is a good few feet below A and C is close to B then when the water flows it should have sufficient pressure to expel the bubble in the airlock.
See also my post on additional thoughts on airlocks dated 5/20/2016
I am intrigued by the airlock relief method described (above) of making a hole/release point at the high point of the bound up line. However I am hesitant to try it since the line is running at partial capacity and does have a vaccum from the force of gravity trying to pull water (and air) down thru the line. I therefore suspect a relief hole will only draw more air into the system rather than let air or eventally water out!? It is a gravity feed system but the line is not a steady downward pitch especially near the top where it starts as a 1″ line for 50′ (the pickup in a brook), then steps up to 1 1/2″ for 200′, then 1 1/4″ for 200″, then 1″ again for 300′ to garden hose– maybe a total of 15 to 20′ vert. drop. Eventually (1st./ last year) the line (mostly) clears of air and runs better but can be quite frustrating waiting and may recur if intake clogs and needs re-priming. I have 3 priming “stations” ; near bottom, a middle spigot and another spigot nearer the top where I can siphon 5 gal. buckets of water into the system and get things started, but if I test lower or middle spigots by cracking open to the air there is suction of air into the line. These spigots are not, however, located at the top of the high points of the line which may rise 1′ at most, probably more like 2 to 6″. So the temtation is to try drilling a hole or two at those high points which I could then plug with a stainless screw. Any ideas? Thanks, Rick; rhcastorh3@gmail.com
It can be frustrating. I read a book on “Chaos” where things happen unpredictably and getting the water to move is a bit like that. As you note, the idea of a hole is to bleed the air out of the airlock and conceptually, the water above the airlock should pressure the air in the lock out through the hole. Your concern is the mass of the water below the airlock will pull air in through the hole. So the outcome may depend on the relative mass of water and diameter of pipes above and below the airlock and the size of the hole. If the airlock you are tapping into is towards the bottom of the line I think the air will be vented through the hole, if towards the top you may get the opposite effect. Actually, even if air enters the airlocked chamber through the hole you have made, the air blockage will have been relieved and water in the line higher up should begin flowing down. The concern will be water flowing out through the hole!
I mentioned chaos seems to rule. Physics principles state that the flow will not be affected by the ordering of the different diameter pipes. However, the challenge is to get the water moving. The flow once it is moving should not be affected by the ordering of the pipes. Intuitively I feel that it will make a difference if you begin the line with the largest diameter pipe then progressing to the smaller diameter pipes. My reasoning is to take it to extremes. Say you have a 2″ pipe and a 0.5″ pipe each 50 ft long. If you use the 2″ pipe first then it will fill with water more easily because there is less/minimal friction. It will almost be as if the brook itself was where the pipe ends. I feel, though this is not scientific and you could argue the opposite, that the water will get into motion quicker this way than if the order were reversed. So you could consider reordering your pipes.
Finally, how do you direct the water from the brook into the pipe. I have different sized funnels for changing oil and one is large with a diameter >1 ft at the open end. If something like this was attached to the pipe in the brook it seems that it would direct and concentrate the flow of the water into the pipe and this could increase the starting pressure. There would be some turbulence since not all the water will go down the pipe but the benefits should offset the water turmoil. A little bit like a hydraulic ram?
Let me know how it goes.
Why not install a small check valve where you are suggesting a small hole at the airlock?
I wrote the post in 2011 and I referred to an “automatic device” – perhaps something that lets air out but not water. A check valve will let out both air and water but will not allow air (or water) to return. I googled and found a device called an air release valve which has a float in it and as the pocket/chamber fills with air it displaces the water level which falls and lowers a float in the chamber which opens a valve to release the air in the chamber/pocket. And the valve closes when all the air is ejected. Pretty nifty but too much for my simple needs and with the particles and debris in my unfiltered water, the float will surely jam. So a check valve may help by not allowing air to re-enter the pipe.
If you have an airlock, the trapped air is under pressure. Therefore when you drill a small
hole at the location of the airlock, air will blow OUT with as much force as there is pressure.
The hole can be tiny: even 1/32 of an inch.
This releases the trapped air (and the airlock) and the water will then flow.
The air can take a while to depressurize if the hole is small. But air will
blow out until the water starts to move.
But you should close the hole after that unless
you don’t mind a tiny amount spraying out. I have used a
band clamp over a bike tube patch to block the hole.
By the way, you have to know where the airlock is located!
Sometimes you can tell by tapping the line to see if it sounds hollow.
I have a gravity feed water system to a mountain cabin.
The system was fine for 40 years (going back before my time),
but due to gradual settling there is now a place where airlocks regularly
develop. If the holding tanks get drained an airlock always developed,
and I just loosen the band clamp to let the air out again.
I suspect that you could blow out the airlock with enough pressure to clear the lock, e.g. a mains pressure water supply hose feeding one end might do it. I have had a similar problem with 100 meters of 13mm hose but was able to clear it by fitting a small plastic tap at the bottom and sucking water down (thru the open tap), then closing the tap between breaths . I kept this up for a few minutes then presto the air bubbles came thru and I had running water.
I’ve been working on my gravity feed water system for several days. It’s been very dry and above ground water has mostly dried up. A bear looking for a drink tore apart my intake system, this in-turn drained my holding tank and water line. I rebuilt everything the bear destroyed, allowed the 325 gal. tank and 600 ft. of water line to fill but had no pressure. I connected a pump at the house trying to suck out the air, still no pressure. I finally found the airlock, it was at the beginning of the water line at the holding tank, I have a capped cleaning port at the shut-off valve, I removed the cap which allowed the airlock to escape, now I have pressure. I replaced the threaded plug with a ball valve to make it easier to relieve any future airlocks.
My thoughts: On systems with low pressure and long line runs a relief valve is needed. Air bubbles travel up the line to the holding tank, with the low pressure the airlock cannot perk into the tank so just add a ball joint to a tee to open and relieve the airlock.
Interesting comments – thanks. I tried something similar. In my post of 6/20/14 I included a photo of 2 of my tanks and if you look at the right tank I have a tee off the exit pipe at ground level with a vertical pipe running above the height of the storage tank (if it didn’t exceed the height of the storage tank, water in the tank would discharge through the pipe). Although the photo shows the vertical pipe is apparently capped, it is open. I believe this has helped water flow.
Is any one know the system of prevention air entrapped after finish of tank water during flow of water (gravity flow of water)
The air is trapped in a pocket because it cannot rise. Bubbles in a vertical pipe of water rise to the top and escape. You should try make the pipe straight and always rising and this will reduce the entrapped air.
I have a water line to my house from a Barried storage tank it is gravity fed to house with a booster pump at house the line is under ground and seems to have a air lock I have tried a shop vac to suck water down but not working any suggestions
Also you may have a blockage or the line may have collapsed at some point. If the diameter is wide enough and the pipe not too long you could try probing with an electrician’s snake. Or try narrow the problem by locating and opening up the line at its midpoint and then at successive midpoints to locate the blockage. If it is an airlock and you know where the downward slope of the line has been interrupted by an upward curve then that would be a good place to find the airlock and if you put a tee with a vertical release pipe and one way valve at the highest point of the curve that should evacuate the air in future. Just some thoughts, I am no expert. See also the preceding comment by a contributor.
Try pumping back up the pipe, not sucking down the pipe
you need to run a small vertical pipe (or hose) from a hole at C to a height above A. That pipe/hose will release air but cannot waste water because water wont go higher than A.
Good suggestion. If you look at the picture in my 5/20/16 post I have something similar – a vertical pipe rising above the level of the water in the storage tank.
There is a great article on this very subject. The key is to increase diameter pipe just before high point and extend over the “hump” where the air sock forms. This allows “sub critical flow” and air to freely accumulates at high point (not as foamy bubbles) and a air reief valve can be set just beyond high point.
Brian
Great article:
http://ceeserver.cee.cornell.edu/mw24/cee332/readings/AirInPipesManual.pdf
Thank you – a nice reference for those interested in the science of air blocks plus practical advice such as at page 62.
They make a small device that has a little float in it. It only let’s air escape from the pipe at the high spot. When the water lifts the float it shuts the valve. I think it cost me around $20.