Why intermittent low pressure in one zone only?

16 years ago

Hello,

We've been experiencing a perplexing problem with our front yard irrigation system that had previously worked perfectly for 15+ years. Four irrigation zones operate normally, but the zone that waters the large lawn area has a problem with inconsistent pressure that began this Spring.

I've had an irrigation repairman out twice, but of course, the zone works perfectly when he is here (turned on at the valve or at the control box) - all pop-ups pop up with good water pressure. At my insistence, he replaced the valve for that zone and also replaced some of the sprinkler heads, but the problem remains.

When I turn the zone on through the control box, either manually or through the timer, 70% of the time there is inadequate pressure to bring all the sprinkler heads up fully - water streams from the bottom of each sprinkler head. There is no other water usage at the house during these times to account for the drop in pressure. I've tried testing the zone at different times of the day, early morning, middle of the day, late at night - doesn't make a difference, sometimes they will work, sometimes not.

I've checked for soggy areas but can't find any.

Does anyone have any other ideas what the cause for intermittent low pressure on one zone?

Thank you!

Linda

Comments (11)

eddywill64
16 years ago
Linda I have a very similar problem and no answer. For me its Zone 2 it will start run for a few minutes then lose pressure - just about shut down all heads then surge back to full pressure. a little while later it will drop out all the way till the heads disappear. It does not happen when I manually run another zone.... I have replaced the valve (I even took and old diagram out cut the entire center out and it still "surged") I have no idea what it is BUT when I run another zone at the same time it does not happen I am lost but working on it!
anotherlinda
Original Author
16 years ago
Hi eddywill64,

Thanks for your reply. I think we must have gremlins!

If you do figure out the cause for the pressure drop, please post it here. I'll do the same.

Good luck!

Linda
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The 'no mixing sprinkler styes rule' doesn't have much to do with pressure, its about application rate and not having one section soggy while the other section is still too dry. Most drip sysems can handle 50 psi, if you're going to mix the zone anyway, I wouldnt bother with a pressure reducer unless your using some real cheap drip brand, it won't affect the amount of water coming out of the emmitters. It's easier to mix a zone with rotors than say spray heads. You can usually nozzle your rotors down so that less water comes out, nozzleing them up might not work, depends on how much of your availabe water is being used already. Drip emmitters also come in sizes. Usually .5, 1 and 2 gpm. really some testing is needed. How long do you usually run the lawn zone and how often? You'll need to choose an emitter size to water your shrubs in the same amount of time. There are also other styles of garden emitters that are individually adjustable, often you can shut them right off, but i find most of them put out a lot of water... if I have to mix a spray zone, thats what I typically use. Hope the rambling helped, I can clarify if it didn't!
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I managed to get the zone back to a working state again: 1. When I took apart the valve assembly box, I noticed the small circular nipple part of the rubber valve was not properly flush in its spot. 2. I thoroughly cleaned all parts in a sink and put the valve box back together (taking care to ensure the nipple and internal rubber valve were properly seated). 3. The pressure problem did still exist, although not as low. I turned down the radius on 2 of the 3 heads back to 180 (leaving one set to 360). This solved it. They all popped up and worked again. My guess is the 9 heads were a little too much for the line to handle. I can open up one head to cover a 360 degree radius, but that is all I can do for that zone. Is it possible to boost the pressure to support all 9 heads on the same zone set to cover a 360 degree radius? If so, can anyone suggest a solution?
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Hello daddylonglegs ... I think you can design your system without a pump ... the trade off will be a bigger watering window .. that is the time your system turns on at night and the time it turns off ... I'm not trying to design your system via computer but for conversation sake only here are some numbers ... lets say you use Rainbird's 3500 series Rotor with a BIG 4.0 nozzle. Running 20 gallons per minute through a 1 inch water meter will cost you about - 3 PSI. A Rainbird 3500 4.0 nozzle needs 25 PSI to spray 31 feet and uses about 3 GPM. Lets say your system needed 12 heads .. that is lets over figure for now since you say you need only six heads ... that would be a total flow of 36 GPM if you ran all the heads at once. Not what we want to do .. Now if you used three valves each to supply 4 heads then each valve would supply 12 GPM. The pressure loss through 100 feet of schedule 40 PVC would be 4 PSI at a flow of 12 GPM. Lets assume you need 150 feet of pipe per valve then your pressure loss would be 6 PSI. So ..- 3 PSI at the meter at 20 GPM - 6 PSI loss at 12 GPM through 150' Sch 40 PVC - 6 PSI Misc pressure loss ( an overly high estimate ) ---------- Thats - 15 PSI... which still leaves you 25 PSI that you need but remember we overestimated here so lets back up .. Lets assume you have a square lawn 65 x 65 feet. It would be better to go with 9 heads BUT a smaller nozzle .. lets say the 1.5 nozzle that will spray 23 feet at 25 PSI and use only 1.06 GPM instead of the 3.0 GPM of a big 4.0 nozzle. This would give you more overlap in the middle where you will need it .. better then six heads which would only just meet in the middle and thats with no wind. At 4 gallons per minute per valve your pressure loss will be .75 for 150 feet of pipe. The meter loss will be much less about 0.1 PSI. So that gives us ... - 0.1 PSI at the meter at 20 GPM - 0.75 PSI loss at 12 GPM through 150' Sch 40 PVC - 6. PSI Misc pressure loss ( an overly high estimate ) ---------- - 7 PSI and leaves 33 PSI more then enough and even room for future pressure loss. Good Day ...
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eddywill64
16 years ago
Linda I am on another forum and I have had some additional questions but nothing yet! are you on a pump or municipal supplied water? Eddy
anotherlinda
Original Author
16 years ago
Hi Eddy - We are on municipal water.
eddywill64
16 years ago
Good Morning Linda so far the consensus is that I have a "porting problem" I will keep you posted. When you operate your weak zone can you manually open another zone and see if the weak zone kicks in better? That is what is helping them diagnose my issues. Eddy
anotherlinda
Original Author
16 years ago
Eddy,

I'm trying to see what happens when two zones are operating at the same time, but can't figure out how to do that. I can start only one zone at a time from the timer/control box.

The new valve the repairman installed has an "On/Off" lever, so I can start that one at the valve, but the other valves only have a type of screw lever at the top of each - I've turned them but nothing happens.

In the next few days I'm going to randomly turn the lawn zone on through the valve lever (not the control box) to see if the pressure varies when started that way. This morning it was very strong and worked perfectly.

I am going to google "porting problem" - though I'm not mechanically minded, it sounds interesting :o)

Thanks for your help!
Linda

The new valve has an easy "on/off" lever.
ronalawn82
16 years ago
another linda & eddywill64, I do believe that you have a 'porting' problem. Here is what I think is happening. The valve opens when the water in the top chamber is led away. This happens when the solenoid opens a port, and the water flows out. This is helped along by a spring pushing on a flexible diaphragm. Visualise a piece of debris in this top chamber finding its way to block the port. The chamber fills up with water and the valve shuts down. The piece of debris sinks and the port is opened once more and the cycle repeats. This would explain the surging BUT I cannot explain how the simultaneous operation of another zone resolves the problem. And sorry, I am too science-minded to believe in gremlins; although I will not walk under a ladder!
anotherlinda
Original Author
16 years ago
ronalawn82,

Thanks so much for your reply.

I'll call a different irrigation repair company and have them check for a porting problem.

I'm very grateful for your and Eddy's advice. Love these boards and the kind folks on them.

Linda
eddywill64
16 years ago
My issue is not resolved yet I am going to replace the whole valve on my zone (i replaced the top half earlier) I will let you know when and if I figure this out!
eddywill64
16 years ago
replaced the whole valve and I checked the intake side check valves for debris and they are all good - still the same problem next trick is to re-plumb all the control valves I will keep you posted - I know this doesn't help you yet but if I make a land mark find then who knows! Eddy
anotherlinda
Original Author
16 years ago
Eddy,

Thanks so much for keeping me posted - I really appreciate hearing what you are doing. I'm keeping my fingers crossed for you!

Why intermittent low pressure in one zone only?

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Why intermittent low pressure in one zone only?

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