Ch 10 pipes and friction loss
when using the friction table, there is a section of pipe sizes, but what does it mean when it says nominal pipe size?
"in name only", so all the pipes mentioned there arent exactly the actually size, like 3/4 pipe isnt exactly 3/4
example 10-6 in ch 10 friction loss is showing how to use the friction table and also find a certain pipe and its friction loss, what would be the answer?
1 1/2 pipe with 20 gpm, would be 1.14 and if it were 100 more ft it would be 1.14 x (200/100) = 2.28psi
3 steps to pipe sizing which ones the first ?
1. Write down the flow of the sprinkler on the plan. It is a good idea to draw a shape around them to keep them organized.
when calculating the dynamic pressure what should be considered ?
1. pressure at the water source, 2.pressure change due to elevation change 3.pressure loss due to friction losses in the pipe 4.pressure losses in valves, meter and other components 5.pressure losses due to fittings
example, what if the line is a 3/4 pipe that measures 42 ft long and has 6 gpm flow. whats the friction loss there ?
1.86 x (42/100) = 0.78 psi, this procedure applies to both short and long lines
whats the answer to example 10-5 in ch 10 friction loss?
120ft + 40ft x 0.433psi = 69.3psi 2.42psi x 280ft = 6.78psi 69.3psi - 6.78psi = 62.5
what are the Several different equations that can be used to calculate friction losses?
Hazen-Williams, Darcy Weisbach and Manning
the formula Ff = P x ^p/L, what does "Ff" mean?
Ff: friction factor (psi/100ft) allowable variation in pressure between the extreme ends of the critical circuit (fraction}
how does length affect friction loss?
Flow through longer Pipes results in greater friction loss at the same flow rate. This is true for all types and sizes of pipe.
the formula Ff = P x ^p/L, what does "P" mean?
P: sprinkler operating pressure at the last sprinkler head on the lateral or the available pressure at the beginning of the pipe network {psi)
whats ANSI/ASAE?
Represents the standard by which the pipe is manufactured.
one of the 4 factors of friction loss is Velocity, what does it do?
Velocity is the speed at which water moves through the system. It is measured in feet per second (ft/s). As velocity increases, friction loss also increases.
3 steps to pipe sizing which ones the second ?
Working back from the farthest sprinkler, determine the flow in the pipe section. Write the flow for that section. Once again, use a distinct shape.
example, from point A to B on a lateral line, will there be friction loss and how would you know ?
YES, theirs always friction loss and you can test it by putting gauges on each end, from the valve itll be high and at the end of the lateral line itll be low, thats friction loss
the formula Ff = P x ^p/L, what does "^p" mean?
^p: allowable variation in pressure between the extreme ends of the critical circuit (fraction}
how would you find the answer to example 10-3 in chapter 10 friction loss in dynamic pressure?
according to the example its 1.83 friction loss, putting it together... 20ft x 0.433 psi = 8.66 60psi + 8.66psi - 1.83psi = 66.8psi
when trying to figure out the velocity with a certain pipe where should you look?
at the friction loss tables that also display the velocities of all pipes and gpm.
how does friction loss affect Dynamic pressure exactly?
change in elevation and turbulence in the moving water and friction between water, the material of pipe, and other components.
the formula Ff = P x ^p/L, what does "L" mean?
critical length of circuit in hundreds of feet [L] is the length over which the allowable pressure variation is measured
how is the actual loss in pounds per square inch determined?
friction loss tables are generally used and calculated using the Hazen-Williams equation.
PE pipe friction tables do not include losses caused by insert fittings, even if they do add friction loss to the pipe, but then how would they cover these losses?
increasing pipe 10 percent is usually adequate, if flow velocities are kept below 5 feet per second.
whats IPS?
iron pipe size, the pipe's outside diameter [OD] dimension corresponds to that of iron pipe. All PVC IPS pipe of the same nominal size has the same OD
3 steps to pipe sizing which ones the third ?
like using the procedure to find the velocity, find the smallest pipe with velocity below 5 feet per second. Write that value above the pipe section.
how would you find the friction loss for other components that may affect?
manufacturers also have friction charts for their valves, backflow prevention devices, and filters. its the same procedure
whats SRD?
the pipes wall thickness as a ratio of the OD, Dividing the OD by the wall thickness gives the standard dimension ratio. All pipe with SDR 21 has the same pressure rating of 200 psi.
it is important to know the friction loss in a irrigation system. if friction loss is too high what could happen?
the pressure at the sprinkler or drip lines will be too low, and it will not operate effectively.
whats C 150
the value of the C factor, which is a measure of the roughness of the inside of the pipe. The lower the number the rougher the surface inside the pipe. For PVC, C=150; for standard steel pipe, C= 100.
whats the shaded parts of the friction loss chart for ?
those are numbers that exceed flow rates of 5 ft per second. it is recommended to be used with caution in a main line, water hammer could occur
why are the friction loss tables used?
to find the pressure loss in the pipe and the velocity at various flow rates. so then can use the appropriate pipe sizes
whats the friction factor method and what should be avoided ?
utilizes a pressure loss limit similar to the velocity limit technique. Once the friction factor is calculated, the designer cannot exceed that loss per 100 feet on any size of pipe. formula: Ff = P x ^p/L
how does roughness affect pressure loss? and what material is best to use instead ?
smooth surface results in lower friction losses. PVC pipe has a smoother inside surface than standard steel pipe. the roughness of the pipe is specified by a roughness factor C-the higher the number, the smoother the pipe.
what are one of the steps to calculating pressure loss in pipes?
Multiply the psi loss by the length of the pipe and divide by 100. The result is the loss of pressure in the length of pipe
whats the standard way to express pressure loss for pipes and tubing? and if more or less than 100ft hows is it measured?
pounds per square inch loss per 100 feet of pipe and the pressure loss for length is increased or decreased proportionally.
if ID of the pipe decreases (with a constant flow) what happens?
pressure loss increases, its best to look at the charts for different pressure losses for different pipes
whats PSI loss and what is it based on?
pressure loss per 100 ft of pipe, in pounds per square inch at the corresponding flow rate. And its based on average wall thickness and average inside diameter
