lawn sprinkler pressure problem

My house came with about 10-12 sprinkler heads connected to one zone for the front lawn. It is close to the water supply (at driveway), even though most people would say there is too many heads.. It used to work somewhat reasonbly. I only noticed one or two heads not popping up, couple months ago.
Today I noticed about 4-5 of the heads that are further down stream, are not popping up. I removed one of these heads and let the water run, and the pressure is weak on those head locations. It seems like the pressure suddenly dropped somewhere in the system, causing the heads downstream to no pop up.
The main question I have is that when I turn the knob of the valve, after a turn or so, the water flow does not appear to increase, is this normal, maybe the valve is damaged and I'm not getting full flow. (I have been turning the knob a bit)
Or I might have a crack somewhere, I do not know the routing of the system so I might have to dig around a bit. I also wondered if there was a rock/debris or something stuck in the system. Which I might need to unearth the pipes to check Or perhaps the water company doesn't have enough pressure lately?
Which should I look into first? I wanted to do a complete re-installation using bigger pipes eventually and less heads, but if I fix this I can wait until next year.
TIA
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1) 10-12 sprinkler heads ... way to many... But we don't know your water source pressure...
2) Have you cleared water out of your sprinkler system before the winter.
3) You probably have crack, so start digging btw the last that has pressure & and first that doesn't.
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Run it for awhile and follow the pipes, try to feel with your feet any extra wet area that may be leaking. often a head or pipe can crack at the base allowing a leak, look for puddling at head bases. Remove the last few heads and check-look inside for dirt-obstructions, and run the line to try to clear it, Probably a crack somewhere in the pipe. Yes the valve could also be bad.
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I started closing the screw on the nozzles of each head so hopefully a leak might show up, no luck, then I started pulling the nozzles off a head and starting the system one by one, I have found a node that shot water 4 ft high (good pressure) but the next node only bubbled 2" high. I might have narrowed down the huge pressure drop location.. I'll unearth the between those connections and see what is up.
Does it hurt anything, like the valve or solenoid, to close the nozzles and pressurize the system like that?
snipped-for-privacy@webtv.net (m Ransley) wrote in message

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I have about 70 lbs static head pressure here, and I have about 10 sprinkler heads per circuit. No problems at all. More sprinkler power than I need. Of course, I have many heads in a small lawn, necessitating attenuation of spray pattern at each head. If I had 10 sprinklers, each blowing at full throttle, then I might see some "droop" in performance.
I believe I used 3/4" sprinkler pipe, instead of 1/2", but I cannot be sure. 3/4" has far better conductivity than 1/2", so I'm not losing much "spraying power" to friction in the delivery piping. Futhermore, as I said, each of my sprinkler heads is constricting the water flow, so I don't have a "virtual hemorrhage" at any one sprinkler head.
If you have a crack, that's a hemorrhage, which will attenuate the pressure available at each sprinkler head in the circuit, both upstream, and especially downstream. This difference will be more noticeable if your distribution piping has high impedance pipes...meaning skinny or obstructed. That's a hint on "where to dig." You can thereby vector your break, by observing your sprinklers...and by looking for a puddle!
For starters, remove all sprinkler heads and blow debris out of the system. If you've got roots in the system, they won't blow out. Watch for patterns, and clear roots where conspicuous.
You'll also need a pressure gauge, to measure your head pressure. There is "static pressure," and "dynamic pressure." Each will tell you plenty. You might not have to do a ton of work, if you finesse this problem. I say 70 lbs static pressure is enough at the sprinkler valve, provided that you have a good main line from the utility's meter. My pipes are in excellent condition everywhere, which might justify why I can put so many heads on one circuit. I have one circuit with dozens of drip-irrigation heads and bubblers on it. I don't let any one bubbler deliver too much water.

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I have a bag full of caps I can screw in place of the sprinkler heads. I cap off all the sprinklers and turn on the water. If there is a bad leak it will usually result in a gusher somewhere in the yard within a few minutes (nice part is that it excavates the hole at the same time). If no gusher, I start at the furthest head and flush the system. Cap off that head and move up to the next. This procedure will help localize an obstruction.
You may be able to clear an obstruction by reverse flushing the pipe. Cap off all heads except the first and last. Attach a garden hose to the last using an adapter and turn on the water so it flows out the first head (opposite normal flow in pipe). Inspect each sprinkler head for root intrusion or insect nests.
Bigger pipes will cut down on chances of obstruction and allow more water to flow to the heads but it will not necessarily help with a low pressure problem. Fewer heads per circuit definately will help with pressure and allow you to program a more effecient use of your water.

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I have a timer operated sprinkler system parts of which are 40 years old. The older parts used that plastic pipe that came in rolls -- ABS?, -- not the modern polyethylene. I have frequent failures that are characterized by the gradually diminishing flow that you observed. These are almost always the result of a pipe which has split to allow gradually increasing leakage and loss of pressure at the heads..
Sometimes the solenoid valves fail, but that usually results in a sudden reduction of the flow to the sprinkler heads.
The pipe leaks are sometimes hard to find. In my case, it helps that I know the routing of the pipes. It could be tough otherwise. As others have said, you first look for overly wet spots above the failed pipe. --- SJF
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