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Planning an irrigation system

Automatic irrigation systems make both environmental and economic sense, and they can be customized to suit all sizes of garden and lawn. With a timer to set your watering schedule for optimum results, you will soon experience the benefits. It’s an eco-friendly way to maintain lawn, garden, vegetable garden and flower beds.

Water pressure and flow

To install an automatic irrigation system on your property you will need water pressure between 30 and 35 PSI (pounds per square inch) and water flow between 10 and 13 GPM (gallons per minute).

Water flow

Your water flow calculation (GPM) will enable you to determine the number of sprinkler heads you can run simultaneously.

  1. Place a one-gallon container under an outdoor faucet.
  2. Time the number of minutes required to fill the container.
  3. Divide the time result into 60, which is your GPM calculation.

For example, if it takes 20 seconds to fill the gallon container: 60 divided by 20 = 3, which means your water flow rate is 3 GPM.

You can also determine the volume of water available for your system (GPM) using your PSI calculations and the size of the main water service line.

Water pressure

To check your water pressure, hook up a pressure gauge to your outdoor faucet (make sure that no other water is flowing inside the home).

Turn on the faucet and record the PSI reading.

Main water service line (from the city main to the house):

  1. Wrap a piece of string around the pipe.
  2. Measure the string.
  3. Determine the diameter using the table below.
Length of String
2"
2-3/4"
3-1/4"
3-1/2"
4-1/4"
Copper pipe size
1/2"
3/4"
1"
PVC or galvanized pipe size
1/2"
3/4"
1"
Length of String
2"
2-3/4"
3-1/4"
3-1/2"
4-1/4"
Copper pipe size
1/2"
3/4"
1"
PVC or galvanized pipe size
1/2"
3/4"
1"

System capacity

Determine the flow-pressure relationship using the PSI measurement from the outdoor faucet and the water supply line dimensions to determine the maximum GPM your system will deliver.

Water Pressure (PSI)

Main line size
35 lbs.
40 lbs.
45 lbs.
50 lbs.
55 lbs.
60 lbs.
65 lbs.
70 lbs.
75 lbs.
½"
3.5
5.0
6.0
6.5
7.0
7.5
8.0
9.0
9.5
¾"
7.5
9.0
10.0
12.0
13.0
14.0
15.0
16.0
17.5
1"
10.0
11.5
13.5
15.0
16.0
17.5
18.5
20.0
21.0
Main line size
35 lbs.
40 lbs.
45 lbs.
50 lbs.
55 lbs.
60 lbs.
65 lbs.
70 lbs.
75 lbs.
½"
3.5
5.0
6.0
6.5
7.0
7.5
8.0
9.0
9.5
¾"
7.5
9.0
10.0
12.0
13.0
14.0
15.0
16.0
17.5
1"
10.0
11.5
13.5
15.0
16.0
17.5
18.5
20.0
21.0

Irrigation system components

Irrigation system components

  • The main sprinkler line to which the valves and valve manifolds will be connected.
  • Header lines which will bring water to your landscape.
  • Lateral pipes connected to the header lines which will feed the sprinkler heads.

Valve or valve manifold

  • Controls the on/off flow of water to each watering “zone.”
  • An assembly of several valves together is called a “manifold.”
  • According to the number of zones in your system, you may need to install more than one valve manifold.
  • Calculate one valve per irrigation zone.
  • Connect the pipes of the main sprinkler line to the header lines.

Certain systems allow you to connect your valve manifold to the water outlet you use to attach your watering hose. This simplifies the installation but is only viable for small-scale use. Larger systems require new piping intended exclusively for the irrigation system installation.

Pipes

Water pressure and volume (flow) will determine the size of the irrigation pipes. If each zone includes the appropriate number of sprinkler heads, you will be able to calculate the quantity of water each head will distribute.

Main sprinkler line

  • Connected in a straight line from the main shut off valve to the valves or manifolds.
  • Usually includes two pipes from the main shut off valve to the front yard manifold and backyard manifold.
  • Must be one size larger than the main water supply line for the house.
  • If the main sprinkler line is ½", limit its total length to accommodate 150 to 200 gallons per minute.

Header lines

  • Attached directly to a zone manifold to supply water to the lateral lines.
  • Intersected by lateral lines.
  • Must be at least 1" in diameter.
  • Sprinklers should not be installed on them directly.

Lateral lines

  • Used to connect each header line to individual sprinkler heads.
  • Must be straight and branch off from the header line to supply water to the sprinkler heads.
  • Must not be smaller than 3/4" in diameter.

Sprinkler head types

Each watering zone will require a uniform sprinkler- head size. Determine the sprinkler head size for each zone. Make sure your design conforms to the maximum number of sprinkler heads per watering zone.

Main types of sprinkler heads

Rotor heads:

  • spray a rotating stream of water up to 360˚ coverage.
  • are suitable for sloping terrain.

Fixed spray heads:

  • disperse water in a fixed pattern.
  • are suitable for strips of lawn and flower beds.

Sprinkler head sizes

The sprinkler head must be the correct size to cover its designated zone.

Large area sprinkler heads

  • Designed for areas 25' x 25' and larger.
  • Spaced 10' to 45' apart.
  • Appropriate for backyards and play areas.

Medium area sprinkler heads

  • Designed for areas smaller than 25' x 25'.
  • Spaced 10' to 15' apart.
  • Appropriate for front yards and side yards. May be spring-loaded pop-up or with adjustable spray and patterns.

Small area sprinkler heads

  • Designed for zones with low-lying vegetation.
  • Spaced 3' to 5' apart.
  • Appropriate for flood watering flowerbeds and groundcover or to spot water trees and shrubs.

System set up

Tips for designing your system

  • On your irrigation plan, place a sprinkler head in each corner. Then use a compass to draw the spraying pattern around each sprinkler head.
  • Add sprinklers along the perimeters and in the center to increase coverage. Adjust spacing.
  • Space the heads at regular intervals and overlap the spray-pattern diameters by 50% to ensure complete coverage.
  • There should be no dry patches remaining.
  • To irrigate narrow strips, use spray heads with strip nozzles. These nozzles typically water areas up to four feet wide.

Measure & draw your property

The first step in planning your irrigation system is to measure your property.

  • Note all measurements, including trees, shrubs, driveway, walkways, tool shed, patio, and all other obstacles.
  • Make a scale drawing on graph paper so you have a top down view of your entire property.
  • Label different areas of the yard, including the lawn, flower beds, container plants, trees, shrubs, and vegetable garden or rose garden if you have one. Each area will represent a different watering zone, with one sprinkler head per watering zone required.

Create watering zones

  • Designate watering zones based on soil conditions, plants to be watered and quantity of water required. Shaded areas of the property will have different needs than full-sun areas, just as certain plants require more water than others.
  • Different types of sprinkler heads should not be used for the same zone: each individual zone will use only one type of sprinkler head.
  • Determine the maximum water flow capacity for each watering zone to make sure the number of sprinkler heads per zone does not exceed this maximum. Manufacturers provide planning guides to help determine maximum water flow and the maximum number of sprinkler heads per zone.
  • Individual zones may use different-sized pipes.
  • Label each watering zone on your plan with the maximum allowable number of sprinkler heads. Include the suggested sprinkler head size (small, medium, large) on the plan.
  • Assign numbers to each watering zone for easy reference.

Design the pipe layout

  • Determine the actual or approximate sizes of the pipes for the entire irrigation system.
  • Draw a direct route for the main sprinkler line from the main shutoff valve or main water supply to the front and backyard manifolds.
  • Draw header lines directly from the manifold to each zone.
  • Draw lateral lines that connect each header line to the sprinkler heads.

Locate the valve placement

  • Determine a logical place for the system’s main shut-off valve. This valve will shut off water to the entire sprinkler system.
  • Connect the main shut-off valve to the sprinkler valve manifolds.
  • Put one manifold in the front yard and one in the back yard.
  • Locate each manifold in an accessible area, away from heavy foot traffic. If possible, locate it on elevated ground to avoid water pooling around it.
  • Clearly indicate the location of the backflow preventer on the drawing

Locate the timer

  • Place the timer close to an available power source where it is easily accessible.
  • Install the timer in a weather-resistant box.
  • Electrical wires will be needed to connect the timer to each manifold valve.
  • Draw lines from the timer to the front and back yard manifolds as well as any additional manifolds required for an extended irrigation plan.

Pro tip

Print out the PDF document so you can note all the necessary measurements and information.

Irrigation system fall preparation

Crib and Bedding

  • System with automatic drain valves: loosen the solenoids on each valve to allow any air inside to escape (gravity will cause the water to flow out of the system).
  • Manual drain valves: installed between the shut-off valve and the valve manifolds, open in the fall to allow water to drain.
  • System without an automatic drain valve:
    • Shut off the main water supply.
    • Set the compressor air pressure regulator to 60 PSI and an air flow rate of 4 and 8 CFM (cubic feet per minute).
    • Blow water out of the pipes and sprinkler heads.
  • When all zones are completely free of water, open up the solenoids on the valves to let out any extra air.

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