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Thursday, August 7th 2014, 8:35pm

Low pressure

Hi all - Long time reader, first time poster. I've been using some suggestions to troubleshoot my system and now Im looking for some more suggestions from you experts. So here's the deal, bought a house last year that had a system installed. Was told that it was a self draining system and from moving a couple of heads I can see there's a tee under each head with one end going to the head, the other going to a self draining valve. The zones are all run with 3/4 inch black irrigation pipe and all of the zones terminate back next to the house in a single valve box that has the valves for all 5 zones. In the house I have a copper manifold that takes a 1 inch feed and breaks it out into multiple 3/4 inch feeds. The sprinkler system attaches here and then converts to 3/4 inch PEX all the way to the side wall where it then turns back into 3/4 inch copper. From there, it goes into the back flow preventer, on the other side of the back flow it is 3/4 inch PVC down to a manifold they built out of 3/4 inch PVC which has all the valves attached.

So.... My problem is low pressure. My biggest zone only has 4 heads and I cant seem to get decent flow out of the zone. The sun finally got hot here in MN and its obvious from the areas of brown grass that the heads are covering close to the head, then at the end of the stream. The middle section just isnt getting enough coverage and the grass is starting to get brown. The heads are all rainbird 5000's and I've tried every adjustment possible. I even changed the nozzlesfrom 2 GPM nozzles to 1.5 to see if I could get better pressure, that didnt seem to help. The bucket test I did seemed to give me about 6 - 6.5 GPM. I have a blow out valve next to the driveway that's always on so I did the test from here since I figured it would be very close to what a zone would see.

The thing that drives me crazy here is my neighbors on either side of me having systems that look like they're on a golf course. Tons of pressure and great coverage and 6 heads per zone. I bought a rainbird pressure gauge and tested my system. I appear to have around 42 PSI. I tried it on my neighbors and he has the same pressure. The only difference between our systems is that he has 1 inch all the way from his main, through his backflow preventer and then at the valve for the zone his change to 3/4 for the zone.

So heres my question. My conversion from 1 inch to 3/4 inch happens at my manifold by the main, his occurs right at his zone valve. Could that make a big difference? Ive read that having 1 inch through a back flow preventer can make a difference. I wouldnt mind running 1 inch to the backflow preventer in the house if I knew it would make a difference. But Im wondering since we have the same pressure if that could really be it. Seems like it could be but Im not sure. I also did a test tonight where I left the pressure gauge connected to the blow out, and the turned on a zone. The pressure dropped as the lines filled, and then once we had water pressure it came back up to about 22. That seems low. Would a bigger pipe help with the pressure?

Any input anyone has would be appreciated!


Supreme Member

Posts: 417

Location: Houston, Texas


Thursday, August 7th 2014, 10:23pm

Also, check to make sure your water meter and all isolation valves are completely open. I have seen people go to expense only to find the meter was Partially open.
:thumbup: :thumbsup:


Supreme Member

Posts: 4,102

Location: Metro NYC


Friday, August 8th 2014, 7:36am

If the static pressure is 42 psi, then you have an uphill battle, and anything that takes away pressure will hurt system performance. So you might certainly consider upsizing the plumbing, starting with the long runs of pipe, both indoors and outside. That said, a flow of 6 to 8 gpm is hardly a killer for 3/4-inch plumbing. If it happens that the neighbors have 1-inch water meters with 1-inch incoming, and you have a smaller meter on 3/4-inch incoming, then you aren't ever going to equal the flow and pressure they have in their sprinkler systems.

You also want to be certain that none of the drain valves in the zones are leaking. You might try capping off all the head connections on one zone and see what results

One thing that a do-it-yourselfer can try on one zone as a last resort, is to switch heads to the best low-pressure performer of all, the Maxipaw impact. They are rarely a pro choice except on 'dirty water' supplies, as pumped from a pond, but they are out there, and they will throw further at low pressure than anything else, period, which gives you the flexibility to tweak their diffusing screws for extra in-between coverage. You would change the stock blue nozzles in favor of the black ones, and adjust the arm springs for low pressure.

This post has been edited 1 times, last edit by "Wet_Boots" (Aug 8th 2014, 8:25am)




Friday, August 8th 2014, 9:46am

Low pressure

Thanks for the input. I've already checked all the valves and it appears that they're fully open.

I should clarify, both the neighbor and I have a 1 inch main line coming in. I think the difference is his goes to a 1 inch manifold and mine goes to a 3/4 inch manifold (on the output side of the manifold). So I have 3/4 inch PEX running to the back flow from the manifold and he has 1 inch.

Im willing to try running 1 inch from my main to the back flow preventer to match what he has, but Im wondering if that will really make that big of a difference. I have 3/4 inch PVC coming off the backflow output down to all 5 valves where as he has 1 inch coming off the backflow to the valves.

I guess my question is, would moving the 1 inch closer to the valves make a significant difference? Since the neighbor has 3/4 inch irrigation in his zones it seems to me that its really just a matter of where we transition from 1 inch to 3/4 inch piping. His is close to the zones and mine is right off my main.

I think the next step for me is to cap all the heads in the zone and see if I see the water meter moving. If I do, I'll likely just take the drains out and see if that helps.

Thanks for all your tips!


Supreme Member

Posts: 4,102

Location: Metro NYC


Saturday, August 9th 2014, 9:31am

Are all of the shutoff valves in the supply plumbing ball valves or gate valves? Is the water meter also a one-inch size? What kind backflow prevention does the system have? What are the lengths of 3/4-inch runs of pipe in the existing system?

Understand that some small amount of 3/4-inch pipe is not enough to account for your troubles. Many homes are supplied by 3/4-inch copper tubing, and have great sprinkler systems anyway.




Sunday, August 10th 2014, 8:11pm

Low pressure

All of the valves are ball valves as far as I can tell. The pipe layout looks like this. Im putting the pipe size in quotes between the items.

Mainline (1 inch) Manifold (3/4 inch pex) back flow preventer (3/4 inch PVC) PVC manifold to split to zones (3/4 inch PVC) valves (3/4 inch irrigation pipe) sprinkler head.

So most of the system is 3/4 inch. Essentially, I only have 1 inch coming in and to the manifold with the water meter in between. A neighbor was telling me that the inside diameter of PVC and PEX can be much smaller than copper. Is possibly an issue?



Posts: 1,520

Location: USA


Sunday, August 10th 2014, 9:08pm

Double check the valve to make sure it's coming on all the way.
How did you test it?
Is the flow control open all the way?
Open the bleeder screw all the way or even take it out. If no bleeder take the solenoid off.
What model valves are they?
That's all I have.
Good luck.




Monday, August 11th 2014, 1:12pm

Low pressure

I've only done the pressure test for far and that I did with a RainBird pressure gauge. I also did the bucket test for GPM which came out to around 6.5.

I've opened the bleeder valves and I get the same pressure as I do when I open the valves electronically. I double checked all the valves last night and they're all open all the way.

I can take all the heads off a zone and plug them to see if the auto drain valves are leaking badly but it seems odd that all zones would have that issue. The only thing I can think of is the 3/4 inch pipe


Supreme Member

Posts: 4,102

Location: Metro NYC


Monday, August 11th 2014, 4:14pm

Unless your pipe runs are hundreds of feet long, you need to keep looking. As it is, the 3/4-inch PVC isn't far from 1-inch copper for inside diameter.

Another idea is to do some flow-and-pressure testing without using the sprinkler system. You got a pressure gauge, so you know the static pressure, and you have a water meter, so you can determine flow rates with the aid of a wristwatch (forget the bucket) while looking at the meter.

By the way, you have been asked direct questions and have failed to answer them. These aren't optional for extra credit, they might be key to solving the issue. So once again, what are the make and model of the zone valves, and of the backflow preventer? How long are the various pipe runs in the supply?




Monday, August 11th 2014, 8:29pm

Low pressure

Hi Wet_boots - Thanks for replying and sorry for not answering your questions.

The valves are RainBird DV-100s (1 inch in and out). The manifold that the installer built out of PVC (made out of 3/4 inch PVC) has 1 inch male screw ends that go onto the valves. From the looks of it, the 3/4 inch black flexible irrigation pipe comes off the other end off of 1 inch adapters screwed into the back side of the valves.

The back flow preventer is a Watts 800M4 1 inch.

So the 3/4 inch copper comes out of the house, goes to a 1 inch adapter into the back flow, then 1 inch coming out of the back flow to 3/4 inch PVC which the entire PVC manifold is built out of but then converts back to 1 inch to go into the valves.

The run from the main in the house to the copper manifold is less than 3 feet

From the manifold I have 3/4 inch PEX to the outer wall and that run is 25 feet.

From the outer wall it transitions to copper to go outside and that run to the back flow preventer is only 2 feet.

My lot is only a half acre and the sprinklers are only on about half of it so from the zone valves (which are all right off the PVC manifold) to each zone have to be pretty minimal.

As far as the flow and pressure testing you are referring to. You're suggesting I measure how much water passes through the meter while running water in the house? Should I just open a couple of the sinks around the house and see how much water passes during a minute?

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