You are not logged in.

Dear visitor, welcome to SPRINKLER TALK FORUM - You Got Questions, We've Got Answers. If this is your first visit here, please read the Help. It explains how this page works. You must be registered before you can use all the page's features. Please use the registration form, to register here or read more information about the registration process. If you are already registered, please login here.

jsbeckton

Senior Member

Posts: 23

Location: Pittsburgh

1

Saturday, October 3rd 2015, 7:05pm

High Pressure but Low Flow

So like many other people around the country I am doing a lot of reseeding this fall due to the hot dry summer. Moving the sprinkler around my 3/4 acre lawn twice a day is not all that much fun so I am thinking about installing a sprinkler system.

It seems the first step is to determine my water pressure and flow rate which I did. I have very high water pressure and actually have a pressure regulator that I can set anywhere between 50-75psi. With the pressure turned all the way up to 75psi I am only getting about 6.7gpm at my hose bib. This seems pretty low so I am fearing that I would need too many zones and was wondering if there is anything else that I can do?

One thing to note is that my hose bib is on a 1/2" copper line tapped off the 3/4" copper main. Would it make any difference if I drew from the 3/4" line to feed the sprinkler system? Wouldn't that still just give me roughly the same 6.7gpm just at a lower velocity? I am guessing this is why they only ask you to test your flow rate through a hose bib even though they will expect you to actually tap into the main for the system.

Thanks for any info that can help!

maximus20895

Active Member

Posts: 36

Location: Knoxville, TN

2

Saturday, October 3rd 2015, 7:45pm

You would most likely be getting around 11 GPM with the 3/4" main line which is what you need to tap into right after the meter. The 1/2" hose bib GPM test is unreliable. You will also have higher PSI than what you mentioned since you will also be tapping upstream of the PRV.

jsbeckton

Senior Member

Posts: 23

Location: Pittsburgh

3

Saturday, October 3rd 2015, 8:08pm

I don't need any more pressure so i was thinking I would tap in downstream of the PRV, and reason not to? Also, how did you get 11 gpm? Thanks.

maximus20895

Active Member

Posts: 36

Location: Knoxville, TN

4

Saturday, October 3rd 2015, 8:35pm

How do you know that you don't need more PSI? Have you calculated the PSI throughout the system? Where is the PRV located? If it is located in the house and you want to tap into to it after it then every time the sprinkler goes off in the morning you will hear the water go through the pipes which is never good at 6AM. Unless you see a huge benefit of tapping after the PRV I would advise against it. You can always buy PRS sprinkler heads, flow control vavles or another $50 PRV to install for just the sprinkler system if you wish.

I got that number based on a chart:




This is assuming you have a 3/4" supply line that is right after the meter and you will be tapping into that.

jsbeckton

Senior Member

Posts: 23

Location: Pittsburgh

5

Sunday, October 4th 2015, 7:30am

The pressure without the PRV is about 120psi, can the sprinkler system handle that because it was splitting my garden hoses. That chart you posted, how can you get flow without any other information than the line size? How do I know I would have a 7 ft/s velocity at that point?

Looks like I already have more flow than that chart indicates at 1/2" so my velocity must be higher at least at the hose bib. Thanks.

This post has been edited 2 times, last edit by "jsbeckton" (Oct 4th 2015, 7:37am)


Wet_Boots

Supreme Member

Posts: 5,124

Location: Metro NYC

6

Sunday, October 4th 2015, 11:11am

Your plumbing can handle the 120 psi, but obviously with some worrisome bumps and bangs in the house when solenoid valves shut off (dishwasher, washing machine)

You can always install a separate reducer in the line that feeds the system, your supply connection being located right after the meter, and have it set higher than the your house pressure, such as 80 psi vs 50 psi in the house plumbing.

mrfixit

Moderator

Posts: 1,991

Location: USA

7

Sunday, October 4th 2015, 11:59am

I have very high water pressure and actually have a pressure regulator that I can set anywhere between 50-75psi. With the pressure turned all the way up to 75psi I am only getting about 6.7gpm at my hose bib. This seems pretty low so I am fearing that I would need too many zones and was wondering if there is anything else that I can do?


Maybe you should install a pressure regulator that can be adjusted from 75 to 150 PSI.
Honeywell has one that can adjust from I believe it's from 15 to 150. If you install the Honeywell take out the adjusting screw and throw it away. It will rust in no time.

I probably shouldn't have called it an adjusting screw. That might confuse things. It's just a screw on top that you have to loosen so you can adjust the pressure. It doesn't really do anything. Leave it off, the pressure can't be changed unless you turn the top by hand. It wont turn by itself without the screw.

This post has been edited 1 times, last edit by "mrfixit" (Oct 4th 2015, 12:04pm)


Wet_Boots

Supreme Member

Posts: 5,124

Location: Metro NYC

8

Sunday, October 4th 2015, 1:57pm

The thing to remember in all this is that the flow you measure from a hose bib is nothing more than the flow you measure from a hose bib. You might easily have double or triple the possible maximum flow (not that you would utilize all of that maximum)

For the do-it-yourself-er, it makes more sense to actually install the plumbing for their system connection, bring it to the outside where the backflow preventer will be, and at that location perform the flow-and-pressure-combined test - the "bucket test"

Don't cheat on the supply pipe diameter. For a 3/4-inch supply line with high pressure feeding it, up-size to 1-inch plumbing. You can, however, use a 3/4-inch pressure reducer to feed the 1-inch sprinkler supply line, and not lose much if any flow capacity because of that choice. I used a lot of Wilkins BR4 pressure reducers, and got some benefit from their being settable to up to 150 psi. (in our current no-lead plumbing scene, the old BR4 became the NR3, with the same internal parts as before)

jsbeckton

Senior Member

Posts: 23

Location: Pittsburgh

9

Friday, October 9th 2015, 11:46am

Well I tapped into the main, upstream of the PCV, and it looks like I have about 23gpm and about 120psi so I will only be restricted by the velocity of flow for my line size which looks to be about 10gpm for a 3/4" line.

Wet_Boots

Supreme Member

Posts: 5,124

Location: Metro NYC

10

Friday, October 9th 2015, 2:21pm

If you include a separate PRV in the system plumbing, you can possibly work with a higher flow, assuming the connection and PRV are right at the water meter location and you have a copper supply line between the house and the street. This is a balancing act that a larger property can require, in order to get watering completed in an acceptable time frame.

Similar threads

Rate this thread