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Did you do any design calulations before doing all of this?

1/2" poly sounds awefully small for pipe to be used. I would assume this is only for your latterals and not for the main too?

[Edit - Short Answer] Friction losses in the 1/2" poly and garden hose are killing your pressure. [/Edit - Original Long Answer]

We need specs on your heads to make accurate calculations. But here's some estimates I come up with assuming your heads are Rainbird 15' nozzles on 1800 series pop-ups, a 180 degree half-circle spray pattern.

Each head needs about 1.5gpm @ 20psi. Five heads would need a total of 7.5 gpm. We'll assume a total of 20psi pressure losses through water meter, backflow device, and irrigation valves. That leaves about 30psi for friction losses. At 7.5 gpm, friction losses will be about 20psi per every 100'. So for the system to operate, your 1/2" pipe can be a maximum of 150' long. Additionally, at 7.5gpm, water will be flowing at almost 8 feet per second through that 1/2" pipe (exceeding the plumbing standard speed limit of 5 feet per second).

If your heads are rotars or have a 360 spray pattern, you're even more screwed.

And even if you were using MP-Rotators (rotators that work at low pressures and less gpm), they still need about 1 gpm per head. So you're still talking 5gpm per zone. That will at least get the flow rate close to the 5 foot per second flow speed limit, but your pressure losses will still be almost 10 psi per 100 foot.

I'm thinking your are going to have to either replace the 1/2" poly with 3/4" poly or replace your heads with MP-Rotators (they only required about 1gpm per head and can throw water 16' with 25psi.)

At the very least, before you bury the pipe, try testing the zones with something larger (diameter) than a 100' garden hose. Get you some 3/4" poly to replace the garden hose, that way you'll only be losing 2-3psi rather than 10-15psi through the supply hose.

But even if a bigger supply hose increases your pressure, I'm afraid you'll still likely be exeeding the recomended 5'/s speed limit. So you might want to consider changing your heads to MP-Rotators if you don't want to replace the poly.

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by mrsafety2</i>
<br />Can you recommend a MP-rotator? Also, does it fit a 1/2" nipple??
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

General Answer:
Check their web site - http://www.mprotator.com/

Detailed Answer:
MP-rotators do not go on 1/2" pvc threads. They replace the spray nozzle in a popup sprikler head such as the Rainbird 1800 series (like the 1804 that you can purchase at Lowes and Home Depot).

And it's not a situation of recomending a particualr MP-Rotator. Basically they are all the same and you just need the particluar one needed for where your spray heads are located.

To backup for a moment, MP-Rotators are a concept. It's basically a spray nozzle (the piece of a popup sprinkler head that directs the water). But where typical nozzles have no moving parts and spray water over the entire area they cover at once, MP-Rotators cover the same area, but with multiple moving narrow streams. So your irrigation system uses fewer GPM to cover the same area (but of course you have to water for a longer period of time to get as much water on the grass).

So when you get into a situation where GPM becomes more important that length of time the system needs to be on, you start looking to MP-Rotators. From there, it's just a question of what you need. MP-Rotators come in 3 basic styles (MP1000, MP2000, MP3000) and a new style for watering strips. The difference between the three basic styles is how far they throw water. MP1000 = about 10 ft, MP2000 = about 20ft, MP3000 about 30ft.

Now one of the other "magical" things about the MP-Rotators is that you can mix and match them on the same circuit. Generally speaking, nozzles can only throw water out to distance between 10 to 15 feet. Then if you want to throw water out 20 to 30 feet, you have to use rotors. But because of the difference in their designed, they each put out a different amount of water when measured in inches per hour. For example, a nozzle might put out 4" of water per hour over the area it covers, while a rotor might only put out 2" of water per hour. So if you have both on the same circuit, the areas feed by the nozzles will get twice as much water as the rotors. But with MP-Rotators, you can have a 10' rotator and a 30' rotator on the same circuit (the penelty being that the 30' rotator will have a much higher GPM than the 10' rotator).

Beyond that, there are then different rotator part numbers for the ones that spray a full circle, a semi-circle between 90-210 degrees and a semi-circle between 210-300 degrees.

So once again, you've got to sit down and do the math. Because you've used 1/2" tubing, regardless of what your water source is capable of in terms of GPM, you have to limit your self to about 5 GPM so that the water speed remains below 5ft/sec. If you were to try to feed 16 gpm into that 1/2" tubing, the water will be moving at about 16 ft/sec (more that three times the "speed limit") and you'd be losing 50+ psi in pressure for ever 100' of tubing.

Now the good news is that the MP2000 rotators use at most 1.01 gpm. So if you needed 5 full circle rotators, you only be needing about 5 gpm total to run the circit. How ever, at 5gpm, you will still be losing 18psi for every 100' of tubing carrying 5gpm. Of course as you get to pipe that is feeding fewwer heads, your pressure losses will decrease. And for the rotators to work, you've got to still have 25 psi of pressure left at the spray head for the rotator to work. And the other thing you will be fighting is that as pressure decreases, the distance even the rotators can throw will be reduced. So it's quite possible that the rotator closest to the water supply will be able to shoot 20', the farthest rotator might only shot 15' because of greater pressure losses due to "friction" losses.