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Friday, April 27th 2012, 11:48am

Flow and pressure over distance

I'm going to install an inground system, myself. I bought a book and read it cover to cover. I'm mostly prepared as far as having the design layout, all measurements accounted for and about 95% of my materials sitting in my garage. However, a discussion with a fellow at Home Depot threw me for a loop. He suggested/adviced that as I use a 1" line into the valves, to use a 3/4" feed line after the valves and then tee off to a 1/2" line to finally feed the heads.
After reading a little more on this (which is not a topic covered anywhere in the "Scotts" book that I mentioned), I'm concerned about reducing the flow rate.
I won't have many turns, will be placing the valves in the zones they serve and will have a static pressure of anywhere from 60lbs. to 100lbs.
Is reducing line size something I should be concerned about?


Supreme Member

Posts: 309

Location: Northern New Jersey


Friday, April 27th 2012, 2:35pm

Hopefully the pros will answer, but here are my thoughts. 1 inch to the valves should be pvc. Either 1 inch or 3/4 inch from the valves should be ok, but bigger the better. That 1/2 inch from the lateral to the heads is a swing joint diameter, should be ok also. And all the heads I have have 1/2 inch inlets. I'm thinking that funny pipe may be 3/8 inch.

Since you like to read, maybe check out Hunters DIY manual. Easy reading, good stuff.


Friday, April 27th 2012, 2:52pm

I have a copy of the Hunter's DIY manual on my desk. It's hard to beat for consumers.
The link is at
You'll have to cut and paste that into your browser.

Pipe size is determined by GPM. Many, many charts available, including HERE.
The Home Depot guy threw out a rule-of-thumb idea. A lot of people use it.
A lot of people regret it.

Understand, when you do the design you might find out you are doing exactly what the guy said.
You might not. But if you do, it will be for the right reasons.

One thing to remember, too big a pipe is always much better than a too small pipe.

Central Irrigation

Supreme Member

Posts: 371

Location: Central Minnesota


Friday, April 27th 2012, 5:57pm

For ease of maintenance....use 1" for everything. If that's what your flows dictate.


New Member


Tuesday, May 29th 2012, 1:49pm

I would not use 3/4" lines. Use 1" line for everything. The only reduction in size should be at the individual heads. There are lots of options for setting up the heads. I prefer to use swing (funny) pipe for the connections to the heads. Some people use risers that are cut off at the height that they need them. There are also saddles that pierce the line and make the connections. I prefer the flexible swing pipe because I have had to move heads at certain times due to lawn or garden bed changes and the swing pip makes it easy to just dig up the connection and change the placement of the heads. You can make up a valve manifold out of pvc if you prefer but the best way is to buy a pre-made manifold with union joints. The manifolds make servicing/replacing valves much easier and sooner or later you will have to repair or replace a valve. Also don't forget a backflow preventer on the main supply to the manifold.

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