Pressure, Flow and Vacuum

[Beltzington]

This is concerns residential water supply but I believe it qualifies as a Hydraulic question.

I want to T my main water supply line with one side going to the house and the other to irrigate the yard. The house side will be pressure regulated at 60psi, the yard side will not and line pressure often exceeds 100psi. Also the yard will be mostly 3/4" pipe and typically is running wide open when watering.

My question is with the yard side with more flow and higher pressure create a vacuum on the house side that could possible suck water out of the house if say a toilet was flushed when irrigating.

I am placing a check valve on the yard side to prevent contaminants from the potable water but was not planning on using one on the house side.

Appreciate your thoughts.

 

[CobyRupert]

My question is with the yard side with more flow and higher pressure create a vacuum on the house side that could possible suck water out of the house if say a toilet was flushed when irrigating.

I'm no expert, but...

Having pressure won't create a vacuum (by definition).
(Ignoring venturi and bernoulli effects. If we can?) :2cents:

I guess you're asking what happens when your house system is charged by the regulator at 60psi from 100psi on the supply side, but then the supply side drops to (say) 40psi because the irrigation is on?

I think (I guess) that yes your house pressure goes to 40 psi (either simultaneously with the supply side pressure drop, or when the first house valve is cracked. - I'm not sure how a regulator would works in this reverse situation), but I doubt it's going to suck a volume of water out of your house. All lines still have positive pressure away from the source.

 

[Beltzington]

Yeah Bernoulli and lift aka vacuum is what put me on this path, I assume like you, that overall system pressure would keep this relatively static but was curious if any had any applied experience. Thanks for your reply.

 

[jenkinsph]

Pressure regulators have a built in check valve so no worries about pulling a vacuum on the house side. Not that it would happen anyway. When I install these PRV's in residential settings I also install an expansion tank by the water heater too. These are small expansion tanks that prevent the cold water filling the water heater from raising the pressure as it heats up.

Plumbing codes require a back flow preventer to keep the irrigation water from getting into the house potable water. In my world a good ball check valve is good enough for this purpose. The only thing that I would expect to happen when using the irrigation system is the house line will drop to the pressure of the irrigation line and result in a lower flow. My sprinklers run from 3am to 6am while everyone is sleeping so not a problem.

I am a master plumber with over 25 years experience.

 

[Beltzington]

Thanks Jenkinsph - Glad to hear I don't need a separate check valve.