Landscape Irrigation

Based upon the book

Rain Bird Irrigation Design Manual

Determine the Available Flow

3 common methods Stopwatch/meter method 5 gallon bucket/stopwatch method Flow meter method

Stopwatch/Meter Method

Locate the first hose bibb in line along the service line Usually has a “shut-off” valve for the house Open the hose bibb Take a water meter reading In one minute take a second reading from the meter

Stopwatch/Meter Method

Determine the difference in the two readings If the meter reads in gallons – you have the flow If the meter reads in cubic feet (cu.ft.) you must convert to gallons per minute

Conversion Cu.Ft. to GPM

1 Cu.Ft. of water equals 7.481 gallons gal/cu.ft.

1 Cu.Ft. = 7.481 gal.

So… Multiply the number of cubic feet from the meter reading times 7.481

Ex.: 1.55 cu.ft. x 7.4871 gal/cu.ft. = 11.6 gal/min.

This answer is in gallons per minute

Conversion Cu.Ft. to GPM

Since the reading was taken after one minute – the answer is in gpm divide by 2… And so on…. or 11.6 gpm If the reading was taken after 2 min. –

5 Gallon Bucket/Stopwatch Method Locate that same first hose bibb Open the hose bibb Stick the bucket under the bibb into the flow Fill the bucket and time how long it takes in seconds

5 Gallon Bucket/Stopwatch Method Here’s the arithmetic: 60 seconds x 5 gallons = # gpm 1 minute time in seconds Ex. 60 seconds x 5 gallons = 12 gpm 1 minute 25 seconds or (60 x 5) ÷ 25 = 300÷25 = 12 gpm

Flow Meter Method

Locate that same first hose bibb – again Attach a “flow meter” to the hose bibb Open the bibb and take the reading – just that simple You also get a static pressure reading

OK…

So we’ve established the flow… And we’ve established the static pressure… And we’re using the worst case too…

And…

With a bit of effort we can determine the : Water meter size – 5/8”, 3/4”, 1”, 1-1/2” & 2” Service line type, size and length Water main type, size and length All of which can be limiting factors for the design

And then…

We take a look at those three “rules of thumb”

Available Flow Rules

These 3 “rules” determine safe flows through the water meter, service line and water main Know these inside and out!

Rule #1 …

Water Meter Pressure Rule or the “10% Rule” Friction loss through the water meter must never exceed 10% of the static pressure on the site Helps prevent heavy pressure loss in the system

Rule #2…

Water Meter Flow Rule Safe flow through a water meter should never exceed 75% of the maximum flow of the water meter This rule is designed to prevent excess demand on the water meter

Rule #3…

Safe Velocity Rule or the “75% Rule” Maximum safe velocity through the service line should never exceed 5 fps for PVC pipe and 7.5 fps for metal pipe Designed to reduce damage to pipe, fittings and valves caused by excess velocities

What if…?

We have a static pressure of 72 psi (WCS) A 1” water meter A 1” Type K copper service with a 10’ rise What is our available flow?

In other words—”how many gallons per minute do we have?” WCS = worst case scenario 

Rule #1… “10% Rule”

How much static pressure can we loose from the water meter?

7.2 or 6.9 psi (if not in the table, round down to the next lowest number in the table for worst case) What flow does that give us? Or how many gallons per minute (gpm) are available?

Water Meter Table Find the correct meter size Locate the correct pressure Locate the flow 34 gpm is the available flow for “Rule #1”

Rule #2… “75% Rule”

How much flow (gpm) can we safely get from the water meter?

The “75% Rule” will tell us that What flow does that give us? Or how many gallons per minute (gpm) are available?

Water Meter Table Find the correct meter size Locate the maximum flow of the meter Determine 75% of the maximum flow 36 gpm is the available flow for “Rule #2”

Rule #3… “Safe Velocity Rule”

Based on the industry standard for safe velocity in pipe, what is the maximum safe flow through 1” Type K copper?

Pipe Table

Find the correct pipe type & size Locate the maximum safe velocity Determine the maximum flow 18 gpm is the available flow for “Rule #3”

The Available Flow Rules Give Us Rule #1 – “10% Rule” gives us 34 gpm Rule #2 – “75% Rule” gives us 36 gpm and Rule #3 – “Safe Velocity Rule” gives us 18 gpm

So…

Which rule produces the limiting factor?

Rule #3 Which element is that?

Type K copper service line What is the available flow?

18 gpm

Moving Right Along. . . .

We’ve establish all of those little details like: Static pressure…and Water meter size…and Service line type, size Any of which can be limiting factors… Giving us the available flow….

The Beginnings of the Design

The available flow tells us what?

Depending on their individual flows, we now know how many sprinklers we can run at any one time No more guessing!

What if…?

We have a static pressure of 68 psi (WCS) A 3/4” water meter A 1-1/4” PE pipe city main with a 10’ rise up to the water meter A 1” Sch 40 PVC service line at 38’ from the meter to the house What is our available flow?

Rule #1… “10% Rule”

How much static pressure can we loose from the water meter?

6.8 or 6.5 psi (if not in the table, round down to the next lowest number in the table for worst case) What flow does that give us? Or how many gallons per minute (gpm) are available?

Water Meter Table Find the correct meter size Locate the correct pressure Locate the flow 20 gpm is the available flow for “Rule #1”

Rule #2… “75% Rule”

How much flow (gpm) can we safely get from the water meter?

The “75% Rule” will tell us that What flow does that give us? Or how many gallons per minute (gpm) are available?

Water Meter Table Find the correct meter size Locate the maximum flow of the meter Determine 75% of the maximum flow 22 gpm is the available flow for “Rule #2”

Rule #3… “Safe Velocity Rule”

Based on the industry standard for safe velocity in pipe, what is the maximum safe flow through 1-1/4” Polyethylene pipe?

Pipe Table

Find the correct pipe type & size Locate the maximum safe velocity Determine the maximum flow 22 gpm is the available flow for “Rule #3a”

Rule #3… “Safe Velocity Rule”

Based on the industry standard for safe velocity in pipe, what is the maximum safe flow through 1” Sch 40 PVC?

Yup, it’s still “Rule #3” but we can call it “Rule #3b”

Pipe Table

Find the correct pipe type & size Locate the maximum safe velocity Determine the maximum flow 12 gpm is the available flow for “Rule #3b”

The Available Flow Rules Give Us Rule #1 – “10% Rule” gives us 20 gpm Rule #2 – “75% Rule” gives us 22 gpm 12 gpm 22 gpm Rule #3a – “Safe Velocity Rule” gives us Rule #3a – “Safe Velocity Rule” gives us

So…

Which rule produces the limiting factor?

Rule #3b Which element is that?

Sch 40 PVC service line What is the available flow?

18 gpm