pvc irrigation system

I'm going to be converting my sprinkler system from black polyethylene piping to pvc. I thought I recalled hearing that one of the advantages of pvc is that one diameter of piping is used throughout, usually 3/4", as opposed to the black poly that decreases in width the further it gets from the pump. But an associate in a store told me today that the same method is used for both: start out larger decrease as you go.
There are 3 zones with 12 - 15 heads on each zone, with some in each zone being 1/2 heads. The pump is 1 1/2 HP.
Will one approach yield better performance than the other?
Thanks.
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On Jan 30, 1:43pm, snipped-for-privacy@ymail.com wrote:

The amount of water that can move through the pipe is a function of the pipe size and will be basicly the same with either pipe material. The PVC could move more water because the connections/ fittings go on the outside of the pipe, where with poly you use barb style fittings, which reduces the pipe diameter at that point.

That rule is generally true for any water supply job. However, whether you can live with one size depends on how many zones you are going to run at the same time, how long the runs are, how many gpm the heads are, etc. If you have a small system with 3 small heads per zone, only run one zone at a time, you could use 3/4" for the whole system.

If you google a bit, you can find irrigation suppliers or manufacturers that have some online tips and layout tools that will be useful.
Before you start, why do you want to convert it to PVC? The black poly pipe is used because it's well suited to the application, ie it's reasonably flexible, can be run around curves, fastens with hose clamps, is cheap, etc.
I
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On Jan 30, 2:51pm, snipped-for-privacy@optonline.net wrote:

I should have mentioned that the heads are "mist" heads not large impluse or rotating heads, and the zones are run one at a time. Thanks.
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On Jan 30, 11:43am, snipped-for-privacy@ymail.com wrote:

Toro's website used to have a pretty good section to help you design your own system. Haven't been there in a while.
Basic process is to lay out your heads and figure out the GPM requirements. You also need to know what GPM your source can supply at the PSI required to pop up the heads reliably. The size of the pipe also factors into what flow you can deliver at what pressure. Then you partition your heads into circuits so you don't exceed the supply GPM on each circuit.
GPM = flow in Gallons Per Minute PSI = pressure in Pounds per Square Inch
Maybe your existing setup can deliver the flow at the necessary PSI to operate reliably with no changes except changing to 3/4 PVC, but it wouldn't hurt to spend an hour or 2 looking at the numbers to avoid unpleasant surprises down the road.
Jerry
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Thanks for the good suggestions.
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