Water Pressure and Different Pipe Sizes

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Started an irrigation project.

There are 4 points in this irrigation system; A, B, C and D.

The main water line to the house is 1" diameter pipe. (Point A)

The distance from Point A to Point B is approximately 30 feet.

Here at Point B the pipe size is reduced down to 3/4" pipe.

The distance from Point B to Point C is approximately 50 feet of 3/4" pipe.

From Point C I have a straight flat 50 foot run of pipe to Point D which will then feed 9 sprinkler heads.

Here is my question:

Will my water line pressure slightly increase or remain somewhat unchanged by dropping down to 1/2" pipe at and after Point D?

I am concerned of pressure loss due to the long distance from Point B to Point D.

Notes: I will be conducting a pressure test at Point C tomorrow 5/24/21 and updating this thread.
 
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  • #2
italicus
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There are differences between theory and pratice, when dealing with real flow problems. Do you know anything about real flow in pipes?
Water is to be considered incompressible, so density remains constant. For reasons of continuity, the flow rate Q = s*v is constant too. Furthermore, there is a “conservation of energy “ theorem, the Bernoulli theorem, where you must take losses of energy into consideration. Note that there are in general losses of energy both distributed and concentrated, when you put any obstacle in the pipe, e.g. a valve or an elbow or a section reduction.
So you will have losses, surely.
 
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  • #3
sophiecentaur
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You need specific data that's been based on loads of practical measurements. There are many sources for this. Here's just one. And here's another.
You'll probably need to spend quite some time on a search engine to get just what you need but I don't think you can just use a theoretical approach.
 
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  • #4
italicus
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Yes, in these problems a pratical approach is preferable.
@sophiecentaur : the links you have given are really good!
 
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Are the pipes horizontal? If not, what are the elevation changes between the ends of the pipes? What is the volume flow rate you are getting with the typical setup? Is the pressure at the house sensitive to the flow rate of water (iow, is there piping resistance inside the home internal piping leading up to the outlet from the house)?
 
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  • #6
sophiecentaur
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Notes: I will be conducting a pressure test at Point C tomorrow 5/24/21 and updating this thread.
This may be an obvious point but the pressure test needs to be done on full flow. Nine sprinklers sounds like quite a high demand in terms of domestic supply. If you first look at the effect of turning on all the sprinklers and seeing how the supply in the house is affected. Thing is, whatever the size of your irrigation system, there may well be just 1/2" pipes into the property (that would be a standard UK situation). The supply pressure may not be much more than 1Bar.
If the supply to the house can handle it then a solution to any losses in your pipe system could be mitigated using a pump. Are you chasing an actual problem here or are you just being careful about your initial design?
 
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Are the pipes horizontal? If not, what are the elevation changes between the ends of the pipes? What is the volume flow rate you are getting with the typical setup? Is the pressure at the house sensitive to the flow rate of water (iow, is there piping resistance inside the home internal piping leading up to the outlet from the house)?
Horizontal,
Today is day one and I am not onsite yet. I will getting all that info today as I need to find psi and flow rate for myself.
Just need to know if if reducing down to 1/2" pipe will help with maintaining current psi due to the long distance from the water main (Point A) where the psi is greatest at that point to Point D.
 
  • #8
gmax137
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Just need to know if if reducing down to 1/2" pipe will help with maintaining current psi
I'm not sure I understand the question here. But reducing pipe size never helps. Unless you're trying to change the flow somewhere else (on a different branch).
 
  • #9
davenn
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But reducing pipe size never helps.

reducing pipe size with distance is standard practice and for example is done in every city/town for water supply
 
  • #10
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The OP has told me that he has found his solution.

Thanks for your participation. Thread closed.
 
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