Pipe diameter

I know there are a lot of variables that go in to this but I am new to this and wondering if there is hopefully an easy answer. I purchased an old home that has an existing irrigation system that pumps water from the lake. The pump is shot and the piping is old copper (I think) that is no good either, so I’m replacing the whole thing. I bought a new pump - I just got the same one that my neighbors use because they all have the same one and I figure it’s for a reason. The outlet from the pump is 1 1/2" but I’m seeing the majority of sprinkler valves are 1". I’ve asked on reddit where is the best place to reduce the pipe and got reamed (for not having a “professional” design). The old pipe is 1" and my neighbor swears the piping near his sprinkler heads is only 3/4" (again, he has the 1 1/2" pipe coming off his pump) so I feel confident reducing to 1" is ok. Long-story-short, does it matter where I reduce the diameter (i.e. closer to the pump or closer to the valve)? Or, should I buy the 1 1/2" valves and reduce to 1" after the valve (although I hope that’s not the case because it seems those are not as readily available and much more expensive)? Thanks!

I assume you have multiple sprinklers off the same loop of pipe. Therefore, you need as much water in the pipework as needed for the combined output of all of the sprinkler heads. But you need more, to have good pressure.

So I would have thought that the best solution is a 1 1/2" backbone, with whatever sprinklers off this.

If you introduce a 1" anywhere on this backbone, you will restrict the flow to that.

Think about the sprinkler furthest away from the pump if it’s a long line. You need the water to get all the way to the end, while all other sprinklers before it gets the water they need.

1 Like

So would you go with 1 1/2” valves? They just seem less available (and more expensive) so common sense just makes it seem they’re not used as much?

You’ll only do the job once. Maybe 1" works, but is largely dependent on the numbers of sprinklers in each zone.

We have a large system with 1 1/2" pipes, but we have 12 or more on some zones

Do you use 1 1/2" valves though? I’ve done a lot of research on the internet and nobody seems to ever really answer this question. It just seems weird that there’s not much info about it and that they are hard to find. Which lends me to think that the standard are these 1" valves which means I need to reduce the pipe at some point? Only one of the zones will be on the larger size while the other 4 will be pretty small, actually.

So if you have therefore got 5 zones, can you split up your big one and definitely go smaller on the pipe size ?

1” valves are standard. Unless you’re planning on digging everything up and starting over you’ll have to reduce to 1” at some point, where that is in relation to the pump really shouldn’t matter.

Thanks. This is what I figured just going on context clues but I’m kind of surprised it’s not really talked about anywhere that I’ve looked on the internet (which is everywhere). I’m sure I’m not the first to encounter this issue. I’m just going to go for it and see what happens. Worst case I have to switch out some pipe but I’m hopeful the current plan will work just fine!

Assuming it was all working before it should work fine with the new pump. Just FYI it’s been several years since I installed my system but I’m almost positive I have a 1” supply line running around the yard that gets reduced to 3/4” downstream of each valve running to the heads. Unless you have a crazy number of rotors on the zones you should be fine.

Most residential pop ups are 1/2" at the sprinkler body. Some rotors can be 3/4". Larger commercial and golf course rotors can be 1"+.

It is hard to say what is “normal”. If you are talking residential track home, it is one thing, but if you are talking about a bunch of high volume, long throw rotors for a LARGE yard, that is another. How many zones are you talking about? How many sprinklers, and what kind of sprinklers in each zone?

As you have found, most residential valves are 1" body. There might be a 1" line feeding a “manifold” setup, but in most cases, 3/4" pipe is run out of the valve to the zone. From there, most get reduced at the sprinkler to 1/2". I wouldn’t plan on running 1-1/2" for long before reducing, unless you have VERY high flow sprinklers, a high quantity of sprinklers per zone, or incredibly long runs. A 1" line can move over 30gpm depending on flow loss.

Not sure how far the lake is from the house… consider running 1 1/2" to the first Tee and then convert to 1". Run all 1" valves and consider filtering, particularly if you use drip or pop up rotors. If you want a hardwired water meter to know what is going on, the everydrop meter is pretty accurate and not expensive for under 20 gpm applications. You need to run a wire for it when you replace the line. Have fun !