msu-ceco/aec_v1 · Datasets at Hugging Face

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Velocity head is usually a small fraction of the total hydraulic head in a pressurized irrigation system, therefore, for the purpose of design it can be ignored.
As water moves through any pipe, pressure is lost due to turbulence created by the moving water.
The amount of pressure lost in a horizontal pipe is related to the velocity of the water, pipe diameter and roughness, and the length of pipe through which the water flows.
When velocity increases, the pressure loss increases.
For example, in a 1-in.
schedule 40 PVC pipe with an 8 gpm flow rate, the velocity will be 2.97 fps with a pressure loss of 1.59 psi per 100 ft.
When the flow rate is increased to 18 gpm, the velocity will be 6.67 fps, and the pressure loss will increase to 7.12 psi per 100 ft of pipe.
The total energy at the pump is determined:
where, H = energy head P = pressure head E = elevation
At any point within a piping system, water has energy associated with it.
The energy can be in various forms including pressure, elevation, velocity, or friction.
The energy conservation principle states that energy can neither be created nor destroyed.
Therefore, the total energy of the fluid at one point in the system must equal the total energy at any other point in the system, plus any energy that might be transferred into or out of the system.
C = conversion constant to convert psi to ft.
In this example, since there is no water flowing, the energy at all points of the system is the same.
Pressure at the microsprinkler is found by solving equation for P:
Reorganization of Eq.
7 results in P=/c
P = / 2.31 = 25.7 psi = 25.7*2.31 = 59.37 ft
Water flowing in a pipe loses energy because of friction between the water and pipe walls and turbulence.
In the above example, when the microsprinkler is operating, pressure will be less than the 25.7 psi due to friction loss in the pipe and the micro tubing.
It is important to determine the amount of energy lost in pipes in order to properly size them.
The Hazen-Williams equation is extensively used for designing water-distribution systems.
The friction-loss calculations for most pipe sizes and water temperatures encountered under irrigation system conditions are shown in Table 1 and Table 2.
The values in Table 1 and Table 2 are computed using the Hazen-Williams equation.
A more accurate equation, Darcy-Weisbach, is sometimes used for smaller pipes or when heated water is being piped; however, the computations are more difficult.
The Hazen-Williams equation can be expressed as:
H = friction loss
Q = flow rate )
D = inside pipe diameter
L = length of pipe , and
C = friction coefficient or pipe roughness
For most irrigation systems a value of C=150 is used which reduces the above Equation to:
The above Equation can also be expressed as:
H=/D487 Eq.
10
where all the terms and units are as defined except that Q has a unit of gallons per minute.
Friction loss in pipes depends on: flow , pipe diameter , and pipe roughness.
The smoother the pipe, the higher the C value.
Increasing flow rate or choosing a rougher pipe will increase energy losses, resulting in decreased pressures downstream.
In contrast, increasing inside diameter decreases friction losses and provides greater downstream pressure.
Determine the pipe friction loss in 1,000 ft of 8-inch Class 160 PVC pipe, if the flow rate is 800 gpm.
Hydraulics of Multiple Outlet System
From Table 1, the I.D.
of 8-inch pipe is 7.961 inches.
From Equation 10:
H1.85 x 1000)/7.961487) H = 9.39 ft
Because of friction, pressure is lost whenever water passes through fittings, such as tees, elbows, constrictions, or valves.
The magnitude of the loss depends both on the type of fitting and on the water velocity.
Pressure losses in major fittings such as large valves, filters, and flow meters, can be obtained from the manufacturers.
To account for minor pressure losses in fittings, such as tees and elbows, Table 3 can be used.
Minor losses are sometimes aggregated into a friction loss safety factor over and above the friction losses in pipelines, filters, valves, and other elements.
Although the HazenWilliams equation facilitates easy manual computations for pipe friction , more complex and accurate methods are also available.
These complex equations are used in several of the currently available computer programs that are used to design microirrigation systems.
For a pipeline with multiple outlets at regular spacing along mains and submains, the flow rate downstream from each of the outlets will be effectively reduced.
Since the flow rate affects the amount of pressure loss, the pressure loss in such a system would only be a fraction of the loss that would occur in a pipe without outlets.
The Christiansen lateral line friction formula is a modified version of the
Hazen-Williams Equation and was developed for lateral lines with sprinklers or emitters that are evenly spaced with assumed equal discharge and a single pipe diameter.
The Christiansen formula introduces a term known as multiple outlet factor "F" in the Hazen-Williams equation to account for multiple outlets:
Hydraulic Characteristics of Lateral Lines
The goal of a good irrigation system is to have high uniformity and ensure that each portion of the field receives the same amount of water.
As water flows through the lateral tubing, there is friction between the wall of the tubing and the water particles.
This results in a gradual reduction in the pressure within the lateral line.
The magnitude of pressure loss in a lateral line depends on flow rate, pipe diameter, roughness coefficient , changes in elevation, and the lateral length.
H = head loss due to friction in lateral with evenly spaced emitters
L = length of lateral
When a lateral line is placed up-slope, emitter flow rate decreases most rapidly.
This is due to the combined influence of elevation and friction losses.
Where topography allows, running the lateral line down-slope can produce the most uniform flow since friction loss and elevation factors cancel each other out to some degree.
F = multiple outlet coefficient
= [1/] + [1/2n] + [05/]
m = velocity exponent ,
Friction loss is greatest at the beginning of the lateral.
Approximately 50% of the pressure reduction occurs in the first 25% of the lateral's length.
This occurs because as the flow rate decreases, friction losses decrease more rapidly.
The lengths of laterals have a large impact on uniform application.
For a given pipe diameter and emitter flow rate, too long laterals is one of the most commonly observed sources of non-uniformity in microirrigation systems.
In general, longer lateral length results in less uniform application rate.
n = number of outlets on lateral,
Q = flow rate in gpm,
D = inside pipe diameter in inches,
k = a constant 1,045 for Q in gpm and D in inches, and
C = friction coefficient: 150 for PVC or PE pipe
Water hammer is a hydraulic phenomenon which is caused by a sudden change in the velocity of the water.
This velocity change results in a large pressure fluctuation that is often accompanied by loud and explosive-like noise.
This release of energy is due to a sudden change in momentum followed by an exchange between kinetic and pressure energy.
The pressure change associated with water hammer occurs as wave, which is very rapidly transmitted through the entire hydraulic system.
If left uncontrolled, water hammer can produce forces large enough to damage the irrigation pipes permanently.
Determine the friction loss in a 0.75-inch poly lateral that is 300 ft long with 25 evenly spaced emitters on each side of the riser.
Each emitter has a discharge rate of 15 gallons per hour.
H F x H Eq.
11
Flow rate into each half of the lateral is: 25 emitters X 15 gph each = 375 gph or 375 gph min = 6.3 gpm
C = 130 for 0.75-inch poly tubing
From Table 4, F = 0.355
From Table 2, the I.D.
of 0.75-inch poly is 0.824 inches
For flow in gpm and diameter in inches the expanded form of the above Equation becomes:
When water is flowing with a constant velocity through a pipe and a downstream valve is closed, the water adjacent to the valve is stopped.
The momentum in water creates a pressure head which results in compression of water and expansion of the pipe walls.

Velocity head is usually a small fraction of the total hydraulic head in a pressurized irrigation system, therefore, for the purpose of design it can be ignored.

As water moves through any pipe, pressure is lost due to turbulence created by the moving water.

The amount of pressure lost in a horizontal pipe is related to the velocity of the water, pipe diameter and roughness, and the length of pipe through which the water flows.

When velocity increases, the pressure loss increases.

For example, in a 1-in.

schedule 40 PVC pipe with an 8 gpm flow rate, the velocity will be 2.97 fps with a pressure loss of 1.59 psi per 100 ft.

When the flow rate is increased to 18 gpm, the velocity will be 6.67 fps, and the pressure loss will increase to 7.12 psi per 100 ft of pipe.

The total energy at the pump is determined:

where, H = energy head P = pressure head E = elevation

At any point within a piping system, water has energy associated with it.

The energy can be in various forms including pressure, elevation, velocity, or friction.

The energy conservation principle states that energy can neither be created nor destroyed.

Therefore, the total energy of the fluid at one point in the system must equal the total energy at any other point in the system, plus any energy that might be transferred into or out of the system.

C = conversion constant to convert psi to ft.

In this example, since there is no water flowing, the energy at all points of the system is the same.

Pressure at the microsprinkler is found by solving equation for P:

Reorganization of Eq.

7 results in P=/c

P = / 2.31 = 25.7 psi = 25.7*2.31 = 59.37 ft

Water flowing in a pipe loses energy because of friction between the water and pipe walls and turbulence.

In the above example, when the microsprinkler is operating, pressure will be less than the 25.7 psi due to friction loss in the pipe and the micro tubing.

It is important to determine the amount of energy lost in pipes in order to properly size them.

The Hazen-Williams equation is extensively used for designing water-distribution systems.

The friction-loss calculations for most pipe sizes and water temperatures encountered under irrigation system conditions are shown in Table 1 and Table 2.

The values in Table 1 and Table 2 are computed using the Hazen-Williams equation.

A more accurate equation, Darcy-Weisbach, is sometimes used for smaller pipes or when heated water is being piped; however, the computations are more difficult.

The Hazen-Williams equation can be expressed as:

H = friction loss

Q = flow rate )

D = inside pipe diameter

L = length of pipe , and

C = friction coefficient or pipe roughness

For most irrigation systems a value of C=150 is used which reduces the above Equation to:

The above Equation can also be expressed as:

H=/D487 Eq.

10

where all the terms and units are as defined except that Q has a unit of gallons per minute.

Friction loss in pipes depends on: flow , pipe diameter , and pipe roughness.

The smoother the pipe, the higher the C value.

Increasing flow rate or choosing a rougher pipe will increase energy losses, resulting in decreased pressures downstream.

In contrast, increasing inside diameter decreases friction losses and provides greater downstream pressure.

Determine the pipe friction loss in 1,000 ft of 8-inch Class 160 PVC pipe, if the flow rate is 800 gpm.

Hydraulics of Multiple Outlet System

From Table 1, the I.D.

of 8-inch pipe is 7.961 inches.

From Equation 10:

H1.85 x 1000)/7.961487) H = 9.39 ft

Because of friction, pressure is lost whenever water passes through fittings, such as tees, elbows, constrictions, or valves.

The magnitude of the loss depends both on the type of fitting and on the water velocity.

Pressure losses in major fittings such as large valves, filters, and flow meters, can be obtained from the manufacturers.

To account for minor pressure losses in fittings, such as tees and elbows, Table 3 can be used.

Minor losses are sometimes aggregated into a friction loss safety factor over and above the friction losses in pipelines, filters, valves, and other elements.

Although the HazenWilliams equation facilitates easy manual computations for pipe friction , more complex and accurate methods are also available.

These complex equations are used in several of the currently available computer programs that are used to design microirrigation systems.

For a pipeline with multiple outlets at regular spacing along mains and submains, the flow rate downstream from each of the outlets will be effectively reduced.

Since the flow rate affects the amount of pressure loss, the pressure loss in such a system would only be a fraction of the loss that would occur in a pipe without outlets.

The Christiansen lateral line friction formula is a modified version of the

Hazen-Williams Equation and was developed for lateral lines with sprinklers or emitters that are evenly spaced with assumed equal discharge and a single pipe diameter.

The Christiansen formula introduces a term known as multiple outlet factor "F" in the Hazen-Williams equation to account for multiple outlets:

Hydraulic Characteristics of Lateral Lines

The goal of a good irrigation system is to have high uniformity and ensure that each portion of the field receives the same amount of water.

As water flows through the lateral tubing, there is friction between the wall of the tubing and the water particles.

This results in a gradual reduction in the pressure within the lateral line.

The magnitude of pressure loss in a lateral line depends on flow rate, pipe diameter, roughness coefficient , changes in elevation, and the lateral length.

H = head loss due to friction in lateral with evenly spaced emitters

L = length of lateral

When a lateral line is placed up-slope, emitter flow rate decreases most rapidly.

This is due to the combined influence of elevation and friction losses.

Where topography allows, running the lateral line down-slope can produce the most uniform flow since friction loss and elevation factors cancel each other out to some degree.

F = multiple outlet coefficient

= [1/] + [1/2n] + [05/]

m = velocity exponent ,

Friction loss is greatest at the beginning of the lateral.

Approximately 50% of the pressure reduction occurs in the first 25% of the lateral's length.

This occurs because as the flow rate decreases, friction losses decrease more rapidly.

The lengths of laterals have a large impact on uniform application.

For a given pipe diameter and emitter flow rate, too long laterals is one of the most commonly observed sources of non-uniformity in microirrigation systems.

In general, longer lateral length results in less uniform application rate.

n = number of outlets on lateral,

Q = flow rate in gpm,

D = inside pipe diameter in inches,

k = a constant 1,045 for Q in gpm and D in inches, and

C = friction coefficient: 150 for PVC or PE pipe

Water hammer is a hydraulic phenomenon which is caused by a sudden change in the velocity of the water.

This velocity change results in a large pressure fluctuation that is often accompanied by loud and explosive-like noise.

This release of energy is due to a sudden change in momentum followed by an exchange between kinetic and pressure energy.

The pressure change associated with water hammer occurs as wave, which is very rapidly transmitted through the entire hydraulic system.

If left uncontrolled, water hammer can produce forces large enough to damage the irrigation pipes permanently.

Determine the friction loss in a 0.75-inch poly lateral that is 300 ft long with 25 evenly spaced emitters on each side of the riser.

Each emitter has a discharge rate of 15 gallons per hour.

H F x H Eq.

11

Flow rate into each half of the lateral is: 25 emitters X 15 gph each = 375 gph or 375 gph min = 6.3 gpm

C = 130 for 0.75-inch poly tubing

From Table 4, F = 0.355

From Table 2, the I.D.

of 0.75-inch poly is 0.824 inches

For flow in gpm and diameter in inches the expanded form of the above Equation becomes:

When water is flowing with a constant velocity through a pipe and a downstream valve is closed, the water adjacent to the valve is stopped.

The momentum in water creates a pressure head which results in compression of water and expansion of the pipe walls.