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mjosephi

New Member

1

Monday, August 20th 2018, 9:51pm

Working pressure drops by 20psi at backflow

Hi all,

I did a pressure test using the mp gauge at the sprinkler heads (considering a rotator nozzle retrofit). The readings vary depending on zone (20-30psi).
I then wanted to check the pressure at the backflow to ensure there is no significant drop there (I connected the gauge to one of the test ports).
With the system off I read 50psi. When the system is running the pressure at the backflow drops by 20psi.
Is this expected or is there some form of restriction before the backflow? I do have a whole house pressure regulator installed where the water comes in from the city.

Pipe size is 3/4".

Should I adjust the whole house regulator or get in touch with the city regarding this issue?

Thanks!

-MJ

mrfixit

Moderator

Posts: 2,295

Location: USA

2

Monday, August 20th 2018, 10:38pm

You need to make sure you have enough pressure with the MP's. Otherwise they wont work.
Optimum working pressure is 40 lbs. I'm thinking you might have trouble with 20-30 lbs.
As far as your reading at the back flow goes, it should read about the same as the MP gauge at the head.

Are you saying that your sprinkler system is running through the pressure regulator of your house? So if you turn the water off to the inside water it also turns off the outside water? What's the pressure before the regulator?

mjosephi

New Member

3

Monday, August 20th 2018, 11:41pm

Thanks for the response.

I concur, the sprinkler pressure now is on the low side - I have toro precision nozzles right now which I believe are ok given this issue and swapped these several years ago as part of a retrofit.

Here is the setup.

Main line comes in at 1". It goes through a whole house PRV then splits to go to the sprinkler system (3/4" line) and the house. The PRV is set at 50psi static pressure.
The PRV is a Wilkins BR4 (1"). Looking at the BR4 pressure drop graph it should only be dropping by a few psi at 5-10gpms.
Given the toro's I doubt that I have a super high water flow - and if I had a leak I am sure my water bills would be high.

I don't know what the city pressure behind the PRV is as I don't have a test port to hook up a gauge to. I would have to inquire with the city.

Not clear at this point if the problem lies with the city or if I have a faulty PRV?

Should I bypass the whole house PRV for the sprinkler supply and regulate that separately perhaps?

mrfixit

Moderator

Posts: 2,295

Location: USA

4

Tuesday, August 21st 2018, 12:45am

I'd separate the two if possible. Maybe check a nearby neighbor's pressure.

Wet_Boots

Supreme Member

Posts: 5,277

Location: Metro NYC

5

Tuesday, August 21st 2018, 1:29pm

Thanks for the response.

I concur, the sprinkler pressure now is on the low side - I have toro precision nozzles right now which I believe are ok given this issue and swapped these several years ago as part of a retrofit.

Here is the setup.

Main line comes in at 1". It goes through a whole house PRV then splits to go to the sprinkler system (3/4" line) and the house. The PRV is set at 50psi static pressure.
The PRV is a Wilkins BR4 (1"). Looking at the BR4 pressure drop graph it should only be dropping by a few psi at 5-10gpms.
Given the toro's I doubt that I have a super high water flow - and if I had a leak I am sure my water bills would be high.

I don't know what the city pressure behind the PRV is as I don't have a test port to hook up a gauge to. I would have to inquire with the city.

Not clear at this point if the problem lies with the city or if I have a faulty PRV?

Should I bypass the whole house PRV for the sprinkler supply and regulate that separately perhaps?
Don't bother with PRV pressure loss charts. There is a hidden requirement that the inlet pressure be at least 50 psi higher than the outlet pressure setting. (this is to assure that the device is fully opened, otherwise the regulating mechanism introduces its own pressure loss on top of the friction loss shown on charts)

The most useful thing to do would be to check with the water department and see what the actual street pressure is.

mjosephi

New Member

6

Wednesday, August 22nd 2018, 9:34am

Thanks for the info.
The city came out and measured the pressure at a fire hydrant outside my house.
It measured 60psi which I guess might explain the issue?
So just bypass the prv for the irrigation supply? Does anyone know if there are blank inserts to essentially neutralize the prv and do a test?
I don't really have an issue with pressure inside the house so could keep the prv for the house supply and just tee off the irrigation before it.

Wet_Boots

Supreme Member

Posts: 5,277

Location: Metro NYC

7

Wednesday, August 22nd 2018, 4:37pm

Thanks for the info.
The city came out and measured the pressure at a fire hydrant outside my house.
It measured 60psi which I guess might explain the issue?
So just bypass the prv for the irrigation supply? Does anyone know if there are blank inserts to essentially neutralize the prv and do a test?
I don't really have an issue with pressure inside the house so could keep the prv for the house supply and just tee off the irrigation before it.
Now you got it.

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