Technical drip problem

rorserSeptember 24, 2012


I hope you might be able to shed some light on an unusual drip irritation problem I am having. Here is the layout for this particular zone:

The solenoid valve with vacuum breaker is at an altitude that is 50 feet above the area being watered by drippers. It releases water into a .70 irrigation line at ~34 psi. Seven hundred feet forward and 50 feet below the water arrives at the area to be dripped at ~56 psi. It then passes first through a professional size filter which has a pressure reducer (20psi) after it and then onto the drippers.

The problem is that when I turn on this system, it often does not emit water. When I open the purge valve of the filter, water and lots of intermittent air are expelled, ant then the system begins to work.

So, do I have some sort of air lock problem? The water is there, the pressure is there, but the water will not leave the system until I purge the filter.

I sure would be grateful for any help you might be willing to offer.

Thanks, Richard

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What size and type is a professional size filter? What is the diameter and material of a .70 irrigation line? Is the source from a lake, reservoir or stream from a pump? If so a strictly drip system may not be the simplest way to go. More info needed to make good suggestions. Aloha

    Bookmark   September 25, 2012 at 9:12PM
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Thanks for the response lehua.
It is the standard size filter with 3/4" female pipe threads on each end. THe S/S filter is a cylinder about 1.5" diameter and 5" long. 0.70" diameter irrigation hose is the standard for professional in CA. The water comes from our hose bibb, nothing exotic like a stream.
I am more concerned about the unusual altitude drop and long run. When the system turns off, the whole 700' of tubing empties and fills with air until the next time the system comes on.
Hope this info. helps.

    Bookmark   September 25, 2012 at 9:56PM
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Two things that I can suggest. 1) Get rid of the filter. It is not needed for municipal water and restricts the flow. If you get dirt in your line from a break then make sure your remove the heads and/or drip lines and flush the mainlines before replacing the spray units. 2) place a small backflow preventer(one-way valve) at the low end of your line to keep the water in the line. On the down stream side of your pressure regulator. As a possible problem solver, add a second pressure regulator(35 psi) upstream of the existing PR. Stepping the pressure down gradually might help with both PR. Your drop is not a problem for the length of your line because you are gaining pressure from the height drop and losing some pressure from the length of the small diameter line(3/4" line is small and limits flow rate. Check your flow rate at the bottom of the hill by filling up a 5-gallon bucket and time it filling. Check from demand flow rate of your drip line and sprayers to see if your maxing out your 3/4" pipe flow rate. JMHO Aloha

    Bookmark   October 2, 2012 at 7:38PM
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>>2) place a small backflow preventer(one-way valve) at the low end of your line to keep the water in the line. On the down stream side of your pressure regulator. The way it is now the water drains out of the 700' tube through the drippers when the valve closes. I don't have a problem with it going back up to the valve. If I put a backflow preventer in the system what would it accomplish and I cannot reverse it or the water would not flow to the drippers.
I have removed the pressure reducer (20psi) and the system does seem to work; I am only worried that the higher pressure (56 psi) may cause the drippers to pop off. They seem to drip OK at that pressure. They are Salco.

    Bookmark   October 2, 2012 at 8:57PM
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I guess I thought the mainline was 700 lf and the dripper section was after that. Miscommunication happens when there is only written words without pictures or being there in person to see the site. Oh well sorry about that. The BFP makes no sense if the run to the drippers is short. The PR also restricts flow. If the drip lines are 700 LF long that is very long for drip lines. Usually the lines are broken up into several segments with solid lateral lines feeding the segments. Each dripper is saps pressure but with a drop of 50 feet in 700 the slope is 7% slope which is quite steep. You might look into placing the drip lines along contour lines of 1.5% or 1.5 feet per 100 feet slope with solid laterals between the contour lines. This creates an even flow from all drippers and will keep the water within the tube lines longer. This also equalizes the pressure to all laterals. If you know your flow rate and pressure before going into the drip and you know the flow rate and pressure loss for the drip line or at each emitter, you can calculate if you have enough flow and pressure to make it to the end of the lines. JMHO Aloha

    Bookmark   October 3, 2012 at 9:38PM
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Sorry for the miscommunication. Now I really have you confused.
From the top:
Holding tank with 5,000 gallons of well water.
Plumbed to a 3/4" pipe that has gravity pressure from the holding tank of ~34psi
On that pipe is an elec. solenoid valve
Next, a backflow preventer
Next, 700' of 0.70 tubing
Next, 50' lower, and at 56psi is a filter
Next about 50' of 0.70 tubing with 1'--3' runs of 1/4" tubing to the plants.
How this clears it up.

    Bookmark   October 3, 2012 at 10:04PM
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How much horizontal and vertical distance does the 3/4" line have? Is the tank under 34 psi pressure from the well pump? Where is the solenoid auto valve located on the 3/4" line? What is the vertical drop distance of the 700' tubing run? What is the horizontal tubing to filter distance? What is vertical distance of 50 ft tubing? My gut feeling without doing calculation is that 3/4 pipe and tubing is not large enough for such a long length of run. It will not be a shortage of pressure with such a drop in vertical distance but the flow rate which is limited by the smaller diameter of conduit used. What is the per foot flow rate of the .70 drip tubing(gph or gpm). JMHO Aloha

    Bookmark   October 4, 2012 at 11:57PM
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Thanks . I think the answers to most of your questions are in my first post.
The tank is just a holding tank. It is nothing more than the water supply Let's just start at the spigot. All the .70 drip tubing is at one level at the bottom, no change of elevation.
Actually, since I removed the pressure reducer, the system seems to be working pretty well. I'll just monitor it for a month or two and see what happens.
Thank you for your help.

    Bookmark   October 11, 2012 at 10:10PM
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I am a licensed landscape contractor in Az. and have quite a bit of experience with drip irrigation. First off at your supply of 34 psi, that is not enough pressure for your system. Second, 700 ft. of drip line is way too much as you will never be able to pressurize the line.I would say just remove the pressure regulator on the drip zone and you should be good.

    Bookmark   November 3, 2012 at 9:49AM
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Thank you Dirty,

The 700 feet is not actually drip line, but rather 3/4" line from the valve downhill to where the plant area is. The valve feeds the 3/4" line which terminates in a normal drip system filter to which is connected a normal length of 0.70" tubing (~35 feet) and off shoots of 1/4" lines attached to the 0.70.
I have removed the pressure reducer, but still the system does not always start with out my purging the air from the system that fills the 3/4" line everytime the system turns off. I had thought of removing the backflow preventer which is at the **top** of the 3/4" line at the electric valve. Might removing that help by not allowing the line to drain each time the system shuts off, thus avoiding the air lock?
Thank you,

    Bookmark   November 3, 2012 at 10:10PM
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