# Water Pressure and Different Pipe Sizes

• DJDV
In summary, the conversation discusses an ongoing irrigation project with 4 points in the system (A, B, C, and D) and varying pipe sizes and distances. The main water line to the house is 1" in diameter, but reduces to 3/4" at Point B and 1/2" at Point D. There are concerns about pressure loss and the need for a pressure test at Point C. There is also a discussion about the differences between theory and practice when dealing with real flow problems in pipes. It is suggested to conduct a search for specific data and consider using a pump to mitigate losses. The conversation also touches on the idea of reducing pipe size with distance being standard practice, but it is noted that reducing

#### DJDV

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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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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sophiecentaur
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.

italicus
Yes, in these problems a pratical approach is preferable.
@sophiecentaur : the links you have given are really good!

berkeman and sophiecentaur
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)?

sophiecentaur
DJDV said:
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?

Chestermiller
Chestermiller said:
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.

DJDV said:
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).

gmax137 said:
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

The OP has told me that he has found his solution.

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sophiecentaur

## 1. What is water pressure?

Water pressure is the force that water exerts on the walls of a container or pipe. It is typically measured in pounds per square inch (psi) and is influenced by factors such as gravity, elevation, and the amount of water in the system.

## 2. How does water pressure affect different pipe sizes?

The size of a pipe can affect water pressure in a few ways. First, a larger pipe diameter allows for more water flow, resulting in higher pressure. Additionally, smaller pipes can cause friction, which can decrease water pressure. Lastly, the length of the pipe can also impact pressure, as longer pipes may experience a decrease in pressure due to gravity.

## 3. How do I calculate water pressure in a pipe?

To calculate water pressure in a pipe, you will need to know the flow rate (in gallons per minute), the pipe diameter, and the length of the pipe. You can use a formula, such as the Hazen-Williams equation, to determine the pressure based on these factors.

## 4. What is the ideal pipe size for optimal water pressure?

The ideal pipe size for optimal water pressure will depend on various factors, such as the flow rate, the distance the water needs to travel, and the elevation changes. In general, larger pipe sizes will result in higher water pressure, but it is important to consider other factors as well.

## 5. How does water pressure impact the overall plumbing system?

Water pressure plays a crucial role in the overall functioning of a plumbing system. Too low of pressure can result in slow flow and inadequate water supply, while too high of pressure can cause damage to pipes and fixtures. It is important to maintain a balanced water pressure to ensure the proper functioning of the plumbing system.

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