Irrigation System Installation & Repair

A good irrigation system puts the right amount of water on each plant and wastes almost none. A bad one floods one corner, leaves another brown, and sprays the sidewalk. Irrigation work mixes basic hydraulics, low-voltage wiring, and plant knowledge. Most problems come from one mistake: asking a water supply to do more than it can. If you understand pressure and flow, the rest of the job makes sense.

What You Will Be Able to Do

• Measure static pressure and available flow at a property
• Group heads into zones that the supply can run
• Install pipe, valves, and heads that are easy to service
• Program a controller for soil, slope, and season
• Track down low pressure, leaks, and electrical faults
• Winterize a system without damaging it

Pressure and Flow

Everything starts with measuring the water supply. Do that before you draw a single line.

Static pressure is the pressure with no water moving. Screw a pressure gauge onto an outdoor faucet or the point of connection, make sure nothing is running, and read it. City water is often 40 to 80 PSI.

Working pressure is the pressure while water flows. It is always lower, because pipe, fittings, valves, and the backflow preventer all cost pressure through friction. The more water you move, the more you lose.

Available flow is how much water the supply can deliver, in gallons per minute (GPM). You can estimate it with a 5-gallon bucket. Time how long the bucket takes to fill from a wide-open faucet, then divide gallons by minutes.

Worked example. A 5-gallon bucket fills in 20 seconds. That is 1/3 of a minute, so 5 divided by 0.33 gives about 15 GPM. Use no more than 75 percent of available flow on one zone, so this property can run about 11 GPM per zone. If each spray head uses 1.5 GPM, you can run 7 heads on a zone.

The Design Triangle

Three things must balance:

• Pressure: How hard the water pushes
• Flow: How much water is available
• Coverage: How far each head throws

Weak coverage from low pressure does not get better with more heads. Each added head uses more flow, so pressure falls further. The fix is fewer heads per zone, larger pipe, or a pump.

Most fixed spray nozzles are built to run at about 30 PSI at the head. Many perform poorly below 20 to 30 PSI. Too much pressure makes mist that drifts away, which is why pressure-regulating heads exist. Rotors usually want more pressure than sprays. Check the nozzle chart.

Pipe Size

Keep water speed under 5 feet per second. Faster water wears pipe and makes water hammer worse. Water hammer is a pressure surge from a valve closing suddenly. Slow-closing valves and arrestors help prevent it.

Actual limits depend on pipe type, so check a friction loss chart.

Parts of a System

Backflow Preventer

Lawn water sits in soil with fertilizer, pesticides, and animal waste. A backflow preventer keeps that water out of the drinking supply, and it is required nearly everywhere. Local rules and the water supplier decide which type you must use.

• Pressure vacuum breaker (PVB): Common on homes. It must sit above the highest head and all downstream piping so that it can break a vacuum. The common rule is at least 12 inches, but check your local code and the maker's instructions. It cannot go below grade.
• Reduced pressure zone assembly (RPZ): Required for high hazards, such as a system with chemical injection. It must stay above grade so that the relief port can discharge into open air.
• Double check valve assembly (DCVA): Allowed in some areas for low hazards.

Testable assemblies are tested by a certified tester, usually once a year.

Controllers and Sensors

• Conventional controllers run on a fixed schedule that you set.
• Smart controllers change the schedule based on weather. Makers often claim they cut water use by 20 to 50 percent. Actual savings depend on how well the old schedule was set.
• Two-wire systems send signals to many valves over a single pair of wires, which helps on large sites.
• Rain sensors stop watering after a set amount of rain, often 1/4 to 1/2 inch. Some states require them. Mount them in the open, not under eaves or trees.
• Soil moisture sensors sit in the root zone and hold off watering when the soil is wet.
• Flow sensors watch flow. A jump points to a break, and the controller can alert you or shut down.

Valves

• Zone valves are electric valves opened by a solenoid. Install them in valve boxes that you can reach.
• A master valve sits at the point of connection and shuts off the whole system when no zone is running. A broken pipe then cannot leak all night.
• Manual drain valves go at low points, so water can leave the lines in winter.

Put a bed of gravel under each valve box. The gravel drains water away, keeps the valve out of mud, and supports the box.

Pipe

Laterals are the pipes downstream of a zone valve. Mainlines stay under pressure all the time, so they need more care.

Heads

The rate column is the precipitation rate, or how many inches of water the head puts down each hour. GPH means gallons each hour.

Never mix spray heads and rotors on one zone. A spray head puts water down far faster than a rotor, so part of the zone floods while the rest stays dry. A nozzle set with matched precipitation applies the same inches of water each hour no matter what its arc is. That is how a half-circle nozzle and a full-circle nozzle stay balanced.

Drip puts water straight at the root zone, so it greatly reduces evaporation and overspray. It needs a filter and a pressure regulator, and you need to check it often, because a clogged emitter gives no visible warning.

Designing the System

1. Measure the water supply first. Find static pressure and available flow.
2. Draw the site to scale, with buildings, hard surfaces, beds, and slopes.
3. Group plants by water need. Turf, shrubs, sun, and shade each get their own zones.
4. Lay out head-to-head coverage. Each head's spray should reach the next head. Anything less leaves dry spots.
5. Add up GPM for each zone, and stay within 75 percent of available flow.
6. Size the pipe to stay under 5 feet per second.
7. Place valves and the controller where people can reach them.

Installing the System

Locate and Dig

Call 811 and wait for marks before you dig. It is the law in every state, and waiting times vary. Dig by hand near marks, and follow your trench safety rules.

Trenchers cut narrow trenches for straight runs. A vibratory plow pulls pipe through the ground with less damage to the lawn, but it struggles in rocky soil and near surface roots. Dig by hand near utilities and tree roots.

Bury laterals about 8 to 12 inches deep. Bury mainlines deeper if your area calls for it, and plan to drain or blow out the system wherever the ground freezes.

Pipe Work

Keep dirt out of open pipe ends. For PVC, follow the cement maker's cure chart before you put pressure on the line. It depends on pipe size and temperature, and in cold weather or on large pipe, a full cure can take 24 hours or more. Many crews wait a full 24 hours as a rule.

For poly, cut the pipe square, push in the barbed fitting, and tighten a stainless clamp on each barb. Do not tighten so far that the clamp cuts the pipe.

Heads and Swing Joints

A swing joint, sometimes built with flexible funny pipe, connects the head to the lateral. It lets you set the head to grade, and it absorbs the hit when a mower runs over the head, so the pipe does not crack.

1. Connect the swing joint to the lateral.
2. Flush the zone for 2 to 3 minutes before installing nozzles. Pipe debris will plug them.
3. Set the head flush with finished grade.
4. Install the right nozzle and set the arc and radius.

Test and Adjust

1. Fill the system slowly to prevent water hammer, and check each joint.
2. Run each zone and walk it. Look for dry gaps, overspray on buildings or walks, and heads that do not clear the grass.
3. If water keeps draining from the lowest heads after a zone stops, add check valves.
4. Program the controller, run a full cycle, and walk it again.

Programming the Controller

• Start time: Early morning, around 4 to 6 AM, gives less wind and evaporation, and the grass dries during the day.
• Run time: Based on the head's rate, the soil, and the plants. Sandy soil takes water fast and dries fast. Clay takes water slowly.
• Watering days: Follow local rules. Where there are none, water deeply 2 or 3 days a week, not lightly every day.
• Seasonal adjust: Set the base program for peak summer, then cut back to about 50 to 70 percent in spring and fall.

Cycle and Soak

Water runs off slopes and clay if it lands faster than the soil can absorb it. Split the run time into short cycles with a soak period between them.

Worked example. A zone on a clay slope needs 21 minutes. Instead of running 21 minutes straight, program three 7-minute cycles with 30 to 60 minutes between them.

Common Repairs

Broken Head

1. Dig around the head and expose the riser.
2. Unscrew the old head.
3. Install the same type and nozzle.
4. Set it to grade and adjust the arc.
5. Run the zone, backfill, and clean up.

Valve That Leaks Through

If heads weep when the zone is off, the valve is not sealing.

1. Shut off the water upstream.
2. Remove the bonnet and solenoid.
3. Take out the diaphragm and spring.
4. Clean the seat of grit.
5. Fit a new diaphragm from a rebuild kit for that model.
6. Reassemble it snug, without overtightening.
7. Turn the water on and test. If it still leaks, replace the valve.

Broken Pipe

Dig out at least 6 inches of good pipe on each side of the break. Cut out the damage. For PVC, use a slip repair coupling or two couplings with a new section of pipe. For poly, use a barbed coupling and clamps. Test under pressure before you backfill.

Troubleshooting

Controllers and valves run on about 24 volts AC, but the controller's power supply is line voltage. Leave that to a qualified person.

Winterizing

Where the ground freezes, water left in the system can crack pipe, fittings, and backflow preventers. Crews usually blow out lines with compressed air before the first hard freeze.

Warning: Compressed air stores a lot of energy, and PVC can shatter. Wear eye protection, stay clear of components while they are under air pressure, and never stand over heads or valves.

1. Shut off the water to the system.
2. Connect the compressor after the backflow preventer, at the blowout port.
3. Set the regulator low. One major manufacturer's limits are 50 PSI for polyethylene and 80 PSI for PVC. Stay below the lowest rating of any part of your system.
4. Open one zone at a time, and blow until only mist comes out. This usually takes 2 to 3 minutes. Do not run air through a dry line, since heat builds fast.
5. Go through the zones a second time.
6. Open drain valves at low points.
7. Disconnect the compressor, and set the controller to Off or Rain.
8. Drain and insulate the backflow preventer following local rules.

In spring, fill the system slowly, with valves partly open, and walk each zone.

Using Water Well

• Audit systems every year for aim, leaks, and overspray.
• Use rotary nozzles or drip where you can.
• Add sensors on systems that lack them.
• Use cycle and soak on slopes and clay.
• Teach property managers how to adjust for each season.

Common Mistakes

Check Your Understanding

1. A 5-gallon bucket fills in 30 seconds. What is the available flow, and how much can you use on one zone?

5 gallons divided by 0.5 minutes is 10 GPM. At 75 percent, that is 7.5 GPM per zone.

2. A customer wants to add heads to a zone with weak spray. What do you tell them?

More heads will make it worse, because they use more flow and lower the pressure. The zone needs fewer heads, better pipe, or more pressure.

3. Heads on a slope run for 20 minutes, and water runs down the sidewalk. What do you change?

Use cycle and soak. Split the time into short runs with soak periods. Rotary nozzles would also help, since they apply water more slowly.

4. A valve clicks when the controller turns it on, but no water flows. What do you check?

The solenoid and the valve itself. The signal is reaching it, so look for a failed solenoid or a clogged port.

Key Takeaways

• Measure static pressure and available flow before you design.
• Use no more than 75 percent of available flow on a zone, and keep pipe speed under 5 feet per second.
• Lay out head-to-head coverage, and never mix head types on a zone.
• Keep PVBs and RPZs above grade and protect the drinking water.
• Flush before you install nozzles.
• Blow out at low pressure and stay clear of the system.