Sprinkler System Low Pressure - sometimes

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Peachlander

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I have a five-year-old, 4 station system sprinkler, two stations higher than the manifold, one lower and one dripper. Orbit valves, Hunter rotator nozzles, Rainbird controller. When I turn on any station, either manualy or via the controller, the pressure is so low I don't get an adequate spray. If I turn the water off at the ball valve, and then on again, I get a rush of pressure and the station works fine. This is frustrating because the system can't be run on a program unless I'm near enough to turn it off and back on again. I've sought advice from my local supplier and they're stumped. Here's what I've done so far:
- Checked for leaks in all stations. None.
- Tested the voltage at the controller and at the manifold. 28v AC on both ends
- Redid the connections at the valves and used new waterproof Marretts
- Bought a new Orbit valve. Same problem with the old or new valve
- Installed backflow check valves at the manifold for the two higher stations
- Removed the filter at the manifold
- Replaced the backflow valve at the shutoff in the mechanical room. This particular valve body has removeable check valves inside. I took them out and tried the system straight, without a check valve. Same problem.
- Programmed the system so different stations come on first, or in different orders

I'm at the end of my rope, and hope this forum can come up with a suggestion or two.

Please help,
 

WorthFlorida

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.......- Replaced the backflow valve at the shutoff in the mechanical room. This particular valve body has removeable check valves inside. I took them out and tried the system straight, without a check valve.
.......- Removed the filter at the manifold


That was my first though, the back flow preventer gets stuck closed. Being lower than the irrigation system, water wants to flow downhill when everything shuts off.
What model back flow is it?
Is this city water or a well (for domestic water)?
"Filter"? Why was it installed? It would be needed with for a well that produces grit.

It also has me perplexed as you did everything I would have done. Is there a Master Valve used? Wires on the MV terminal of the controller would indicate there is one. Well/pump only irrigation uses the MV terminal to activate the motor start relay and I don't believe you have one.

Is there a spigot or valve after the back flow preventer in the basement wall or exterior wall such as a crawl space that would allow the system to be drained for the winter months? If there is one, when it is opened does the water flow at full force?
 
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Peachlander

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That was my first though, the back flow preventer gets stuck closed. Being lower than the irrigation system, water wants to flow downhill when everything shust off.
What model back flow is it?
Is this city water or a well (for domestic water)?
"Filter"? Why was it installed? It would be needed with for a well that produces grit.

It also has me perplexed as you did everything I would have done. Is there a Master Valve used? Wires on the MV terminal of the controller would indicate there is one. Well/pump only irrigation uses the MV terminal to activate the motor start relay and I don't believe you have one.

Is there a spigot or valve after the back flow preventer in the basement wall or exterior wall such as a crawl space that would allow the system to be drained for the winter months? If there is one, when it is opened does the water flow at full force?
Thanks for the reply. The backflow preventer is designed for sprinkler systems. Watts 3/4 x 3/4 LF7RU2-2. This valve allows the two interior flappers to be removed. I tried removing one, then both. Same problem either way. Domestic water. ~100 psi at the manifold. (Supply is before the regualtor). No master valve. No drain spigot, although I blow out the syystem and leave the ball cock open at the manifold in winter to prevent trapped water from freezing. The filter is a typical grit (diagonal) in-line filter right before the manifold. You can take the little basket out to clean or can operate without (which I did).
 

WorthFlorida

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Your original post read "replaced Orbit valve". Which one? Obviously with four zones there will be four valves. My thought on a spigot is to run water before and after all components.

Is the regulator for high pressure city water? I'm assuming you have a pressure reducing valve.

I think this may prove where the problem is, first I'm assuming that this is a new problem after four years. When you have the low pressure condition, do not turn off the irrigation but open a faucet or hose spigot before the irrigation system but after the regulator. At the faucet or spigot if the pressure is also low, suspect the pressure regulator. If the pressure is high and the irrigation pressure jumps up, the pressure regulator is a strong suspect as the problem.

When a irrigation valve opens, there is hardly any back pressure until the zone if full of water since it can drain out while idle. With the rapid rush of water the regulator may have lost its calibration. The fix would be a rebuilt kit for it.

If all four zone valves are off a manifold, opening (or adding) a spigot before the manifold will prove the water flow is low or high. If you know where the first sprinkler heads are after the zone valve, remove the sprinkler completely or if they are popup, remove the spray head. With full pressure the water should shoot up quite high.
 

Peachlander

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Your original post read "replaced Orbit valve". Which one? Obviously with four zones there will be four valves. My thought on a spigot is to run water before and after all components.

Is the regulator for high pressure city water? I'm assuming you have a pressure reducing valve.

I think this may prove where the problem is, first I'm assuming that this is a new problem after four years. When you have the low pressure condition, do not turn off the irrigation but open a faucet or hose spigot before the irrigation system but after the regulator. At the faucet or spigot if the pressure is also low, suspect the pressure regulator. If the pressure is high and the irrigation pressure jumps up, the pressure regulator is a strong suspect as the problem.

When a irrigation valve opens, there is hardly any back pressure until the zone if full of water since it can drain out while idle. With the rapid rush of water the regulator may have lost its calibration. The fix would be a rebuilt kit for it.

If all four zone valves are off a manifold, opening (or adding) a spigot before the manifold will prove the water flow is low or high. If you know where the first sprinkler heads are after the zone valve, remove the sprinkler completely or if they are popup, remove the spray head. With full pressure the water should shoot up quite high.
Thanks agian for your reply. The system is supplied before the regualtor, so I don't think it's a regulator problem. The only thing I can think of now perhaps a sloppy job (my own) when I replaced the frozen, then cracked, ball valve on the PVC pipe just before the manifold. Perhas a piece of crap is flopping around in the joint when I replaced it? I tried flushing it out by opening the cap at the end of the manifold run and giving 'er a good flush, and tied the toe of a pantyhose over the end to catch any crap. Nothing.
 

WorthFlorida

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A ball valve is nearly the same size opening of the pipe inside diameter. When things get caught up inside the pipe, it's usually at a 90º elbow. Small stones just wont take the turn. No matter how careful, I've been caught myself with blocked pipe because somehow debris or stones get inside the pipe and not seen.

Again, remove the first sprinkler of each zone and try it out. If there is low pressure as usual, then the problem in somewhere at the manifold/zone valves.
 
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