Irrigation System Installation & Repair

A well-designed and properly installed irrigation system keeps landscapes healthy while conserving water. Irrigation work combines plumbing skills, electrical knowledge (low voltage), hydraulic principles, and an understanding of plant water needs. This guide covers comprehensive installation procedures, common repairs, system design basics, and seasonal management for professional landscape irrigation.

Hydraulic Fundamentals

Before installing or troubleshooting any irrigation system, you need to understand the hydraulic principles that govern how the system works.

Pressure

• Static pressure - The water pressure in the system when no water is flowing. Measured at the point of connection with a pressure gauge. Typical municipal water pressure ranges from 40-80 PSI. You need at least 30 PSI at the sprinkler heads for proper operation.
• Dynamic pressure (working pressure) - The pressure when water is flowing through the system. Always lower than static pressure because friction loss occurs as water moves through pipes, fittings, and valves. The more water flowing, the greater the friction loss.
• Pressure loss - Calculate friction loss through each component: pipe (based on pipe size, length, and flow rate), fittings (each fitting adds equivalent pipe length), valves, and the backflow preventer. If your total pressure loss exceeds the available pressure, the system will not perform properly.

Flow Rate

• Available flow rate - How much water the supply can deliver, measured in gallons per minute (GPM). Determine this by timing how long it takes to fill a 5-gallon bucket from an outdoor hose bib with the valve fully open. If it fills in 20 seconds, your flow rate is approximately 15 GPM (5 gallons / 0.33 minutes = 15 GPM).
• Zone flow - Each zone's total flow (the sum of all sprinkler head GPM ratings on that zone) must not exceed 75 percent of the available flow. Exceeding the available flow causes low pressure, poor coverage, misting, and wasted water.
• Pipe sizing - Pipe must be sized to carry the required flow without excessive velocity. Maximum water velocity in irrigation pipe should be 5 feet per second. For 3/4-inch pipe, the maximum recommended flow is about 8 GPM. For 1-inch pipe, about 14 GPM. For 1.25-inch pipe, about 22 GPM.

The Design Triangle

Every irrigation design balances three factors:

1. Pressure - How much force pushes the water
2. Flow - How much water is available
3. Coverage - How far and wide each head throws water

If any one of these is insufficient, the system underperforms. You cannot fix low pressure by adding more heads - you make it worse. You cannot fix low flow by increasing pipe size alone. Understanding this triangle helps you diagnose most system problems.

System Components

Water Source and Backflow Prevention

• Water source - Most residential and commercial systems connect to the municipal water supply through a dedicated irrigation meter or a tap off the domestic service line. Wells and pump systems from ponds or lakes are used in rural and agricultural settings.
• Backflow preventer - Required by plumbing code in virtually all jurisdictions. Prevents irrigation water (which may contain fertilizer, pesticide, or soil bacteria) from flowing back into the potable water supply. Common types:
  • Pressure Vacuum Breaker (PVB) - The most common type for residential systems. Must be installed at least 12 inches above the highest sprinkler head. Cannot be installed below grade.
  • Reduced Pressure Zone Assembly (RPZ) - Required for commercial systems in most jurisdictions and for systems with chemical injection. Can be installed below grade in a vault. Must be tested annually by a certified tester.
  • Double Check Valve Assembly (DCVA) - Allowed in some jurisdictions for non-health-hazard applications. Can be installed below grade.

Controllers

The controller (timer) is the brain of the irrigation system.

• Conventional controllers - Timer-based. The operator sets specific start times, run times, and watering days for each zone. Simple and reliable.
• Smart controllers (weather-based) - Automatically adjust watering schedules based on local weather data, soil type, plant type, slope, and sun exposure. Can reduce water use by 20-50 percent compared to conventional controllers. Increasingly required by water conservation ordinances.
• Two-wire systems - Advanced controllers that communicate with field-installed decoders via a single pair of wires rather than individual wires to each valve. Common in large commercial and golf course irrigation. More efficient for large systems with many zones.
• Flow sensors - Connected to the controller to monitor water flow. Can detect breaks (high flow) and alert the operator or automatically shut down the system to prevent waste and property damage.

Valves

• Electric zone valves - Solenoid-operated valves that open and close in response to signals from the controller. Available in 3/4-inch through 3-inch sizes. Install in valve boxes at accessible locations.
• Master valve - A valve installed at the point of connection that shuts off water to the entire system when no zones are active. Prevents water loss from leaks when the system is off. Highly recommended for all commercial systems.
• Manual drain valves - Installed at low points in the system to allow water to drain for winterization. Use in addition to (not instead of) compressed air blowout.

Pipe and Fittings

• PVC (polyvinyl chloride) - Rigid pipe joined with solvent cement (primer and glue). Available in Schedule 40 (standard) and Class 200 (lighter wall, suitable for most irrigation mainlines). The most common choice for mainlines and lateral lines in moderate climates.
• Polyethylene (poly pipe) - Flexible black pipe joined with barbed fittings and clamps. More resistant to freezing and ground movement than PVC. Common for lateral lines in cold climates and for drip irrigation systems.
• Swing joints (funny pipe) - Flexible risers that connect the lateral pipe to the sprinkler head. Allow 6-12 inches of flex so the head can be adjusted to grade without stressing the pipe. Standard practice for all head installations.

Sprinkler Heads

Choose the right head type for each area:

• Pop-up spray heads - Fixed spray pattern, 4-15 foot radius depending on the nozzle. Available in 2-inch, 3-inch, 4-inch, 6-inch, and 12-inch pop-up heights. Use 4-inch or 6-inch pop-up in turf (taller to clear the grass blades). Precipitation rate: typically 1.5-2.0 inches per hour. Best for small to medium turf areas, flower beds, and narrow strips.
• Rotary nozzles (MP Rotators, R-VAN) - Rotating streams that cover a 15-35 foot radius. Lower precipitation rate (0.4-0.8 inches per hour) than spray heads, which means less runoff on slopes and clay soils. More wind-resistant than spray heads. Increasingly popular for medium-sized areas.
• Rotor heads - Gear-driven heads that rotate through an adjustable arc, covering a 25-50+ foot radius. Precipitation rate: typically 0.5-1.0 inches per hour. Best for large turf areas, athletic fields, parks, and commercial landscapes. Available in residential (small rotor) and commercial (large rotor) sizes.
• Drip irrigation - Low-volume emitters that deliver water directly to plant roots at 0.5-4.0 GPH (gallons per hour) per emitter. Inline drip tubing has emitters built into the tubing at set intervals (6, 12, 18, or 24 inches). Best for shrubs, trees, flower beds, and container plantings. Conserves water by minimizing evaporation and runoff.

Critical rule: Never mix head types on the same zone. Spray heads, rotary nozzles, rotors, and drip all have different precipitation rates. Mixing them on one zone means some areas get too much water while others get too little. Each head type must be on its own zone.

Installation Process

Design

Before any installation, a system must be designed:

1. Measure the property - Create a scaled drawing showing buildings, hardscape, planting areas, slopes, and obstacles.
2. Determine water supply - Measure static pressure and available flow at the point of connection.
3. Identify plant zones - Group areas by water need (turf, shrubs, annual beds, shade vs. sun). Each group becomes a separate zone.
4. Select head types and spacing - Match head types to the areas they serve. Space heads for head-to-head coverage (the spray from one head should reach the adjacent head). This is critical for uniform coverage.
5. Calculate zone flow - Add up the GPM of all heads on each zone. Verify it does not exceed 75 percent of available flow.
6. Size pipe - Select pipe sizes that keep velocity under 5 feet per second at the design flow rate.
7. Plan valve and controller locations - Valves should be accessible for maintenance. The controller should be in a protected, accessible location with power available.

Utility Locating

Call 811 before digging. This is not optional. It is the law in all 50 states. The utility locating service will mark underground gas, electric, water, sewer, cable, and telephone lines within 48-72 hours (varies by state). Striking a utility line can cause serious injury, property damage, and significant financial liability.

After utilities are marked, respect the marks:

• Maintain 18-24 inches of clearance from marked utility lines when trenching
• Hand-dig within 18 inches of any marked utility
• If you cannot avoid crossing a utility, hand-dig to expose it and carefully route your pipe over or under it

Trenching

• Trenching machine - A walk-behind or ride-on trencher cuts a narrow trench (typically 3-6 inches wide). The standard tool for straight runs. Dig 8-12 inches deep for mainlines and laterals. In cold climates, bury pipe below the frost line or winterize the system.
• Vibratory plow (pipe puller) - Pulls pipe directly through the ground without an open trench. Faster and less disruptive to the landscape than trenching. Common for long runs in open areas. Does not work well in rocky soil or near surface roots.
• Hand digging - Required near utilities, in tight spaces, and around tree roots where machine damage would occur. Use a flat-bottom spade for clean trenches.
• Trenching tips - Keep trenches straight. Remove loose soil from the trench bottom. Maintain consistent depth. Set excavated soil to one side for clean backfill.

Pipe Installation

PVC Solvent Welding:

1. Cut pipe square using a PVC pipe cutter or a saw (clean up burrs with a deburring tool or knife)
2. Dry-fit the joint to verify alignment
3. Apply purple PVC primer to both the pipe end and the inside of the fitting socket. Prime generously.
4. Apply PVC solvent cement to both surfaces. Apply cement to the pipe first, then the fitting.
5. Insert the pipe into the fitting with a quarter-turn twist and hold for 10-15 seconds. The twist distributes cement evenly.
6. Wipe away excess cement. Allow joints to cure before pressurizing (minimum 15 minutes for small pipe in warm weather, up to 24 hours for large pipe or cold weather per cement manufacturer instructions).

Poly Pipe:

1. Cut pipe square
2. Insert the barbed fitting into the pipe
3. Secure with two stainless steel clamps on each side of the fitting barb
4. Tighten clamps firmly but do not overtighten (which can cut the pipe)

Head Installation

1. Connect a swing joint (funny pipe assembly) to the lateral line using a tee or saddle fitting
2. The swing joint should have at least two elbows to provide flexibility for grade adjustment
3. Set the head at the finished grade level. The top of the head should be flush with the surrounding soil surface.
4. Before installing nozzles, flush the system by running each zone for 2-3 minutes. This clears dirt, shavings, and debris that would clog the nozzles.
5. Install the correct nozzle for the coverage area (full circle, half circle, quarter circle, or adjustable arc). Adjust the radius and arc per the design.

System Testing and Adjustment

After installation is complete:

1. Pressurize the system slowly. Check for leaks at every joint.
2. Run each zone and walk the property. Verify:
   • Head-to-head coverage (no dry gaps between heads)
   • Correct arc and radius on every head
   • No overspray onto buildings, sidewalks, parking areas, or streets
   • Proper pop-up height (heads clear the grass blades when operating)
   • No low-head drainage (water draining from the lowest heads after the zone shuts off - install check valves if needed)
3. Program the controller with appropriate schedules. See Controller Programming section below.
4. Run a full cycle and re-walk to verify coverage uniformity.

Controller Programming

Scheduling Basics

• Start times - Set the time the system begins watering each program. Early morning (4-6 AM) is ideal: lower wind, lower evaporation, lower demand on the municipal system, and the turf dries before nightfall (reducing disease). Avoid watering between 10 AM and 6 PM.
• Run times - Set how many minutes each zone runs. Base this on the sprinkler precipitation rate and the soil type:
  • Sandy soil: absorbs water quickly, runs shorter and more frequently
  • Clay soil: absorbs water slowly, needs shorter run times with soak-in pauses (cycle-and-soak) to prevent runoff
  • Loam: moderate absorption, standard run times
• Watering days - Select days based on local watering restrictions (many municipalities have 2-3 day per week limits). Where there are no restrictions, water deeply and infrequently (2-3 times per week) rather than lightly every day.
• Seasonal adjust - Most controllers have a percentage adjustment feature. Set the base schedule for peak summer demand, then reduce the percentage in spring and fall:
  • Summer: 100 percent
  • Spring: 50-70 percent
  • Fall: 50-70 percent
  • Winter (warm climates): 20-30 percent

Cycle and Soak

For slopes, clay soil, or compacted areas where runoff is a problem:

• Instead of running a zone for 20 minutes straight, split it into three 7-minute cycles with 30-60 minutes between cycles
• This allows water to soak into the soil rather than running off
• Most modern controllers have a built-in cycle-and-soak feature

Rain Sensors and Smart Controls

• Rain sensors - A simple device that interrupts the irrigation cycle after a set amount of rainfall (typically 1/4 to 1/2 inch). Required by law in many states (including Florida, New Jersey, Connecticut, and others). Mount the sensor in an open area exposed to rainfall, not under eaves or tree canopy.
• Soil moisture sensors - Installed in the root zone, these measure actual soil moisture and override the controller when the soil is already wet. More accurate than rain sensors.
• Weather-based smart controllers - Use ET (evapotranspiration) data from local weather stations to calculate how much water the landscape actually needs each day. Adjust automatically. Can reduce water consumption by 20-50 percent.

Common Repairs

Broken Sprinkler Heads

The most common irrigation repair:

1. Dig around the head carefully to expose the swing joint connection
2. Unscrew the old head from the swing joint riser
3. Install the new head. Match the original head type, model, and nozzle. Mismatched heads on a zone cause uneven coverage.
4. Set the new head at grade and adjust the arc and radius
5. Run the zone to verify operation
6. Backfill and clean up

Leaking Valves

The most common valve repair is a diaphragm replacement:

1. Turn off the water supply upstream of the valve
2. Unscrew the valve bonnet (top cap) and solenoid
3. Remove the old diaphragm and spring
4. Inspect the valve body seat for debris or damage. Clean with a cloth.
5. Install the new diaphragm (available in rebuild kits specific to the valve brand and model)
6. Reassemble the bonnet and solenoid. Hand-tighten, then snug slightly with a wrench. Do not overtighten.
7. Turn on the water and test. If the valve still leaks through (water running from the heads when the zone is off), the valve body may need replacement.

Broken Pipes

1. Dig out the break, exposing at least 6 inches of undamaged pipe on each side
2. Cut out the damaged section with a PVC cutter or hacksaw
3. For PVC: splice in a new section using a telescoping repair coupling (one end slides to accommodate the fixed pipes) or two couplings and a short pipe section. Primer and cement all joints.
4. For poly: cut out the damaged section and reconnect with a barbed coupling and clamps
5. Pressure test before backfilling

Low Pressure on a Zone

Systematic troubleshooting:

1. Check for obvious leaks (water surfacing, unusually wet areas, running water sounds)
2. Verify the valve is fully open (partially closed valves restrict flow)
3. Check the backflow preventer - some have shut-off valves that may be partially closed
4. Count the heads on the zone and calculate the total GPM. Compare to the available flow. An over-populated zone will have low pressure.
5. Check for clogged nozzles or filters in the sprinkler heads
6. Check the master valve (if installed) for obstruction

Controller Issues

• System does not run - Check power (plug, breaker, GFCI). Check the backup battery. Verify a program is actually set (start time, run time, and watering day).
• One zone does not come on - Check the wire connection at the controller. Use a multimeter to check for continuity on the wire pair to that valve. Check the solenoid at the valve (a failed solenoid clicks when energized but the valve does not open - replace the solenoid).
• System runs at wrong times - Check the AM/PM setting. Verify the current time and date are correct. Check that multiple start times are not set (each start time runs the entire program).

Winterization

In any climate where ground temperatures drop below 32 degrees Fahrenheit, the irrigation system must be winterized to prevent freeze damage. Frozen water in pipes expands and cracks PVC, breaks fittings, and destroys backflow preventers.

Blowout Procedure

1. Shut off the water supply to the irrigation system (at the isolation valve or irrigation meter)
2. Connect an air compressor to the system. Use the blowout port on the mainline or connect at a convenient point after the backflow preventer. The compressor should deliver at least 50 CFM (cubic feet per minute) for residential systems, 80-185 CFM for large commercial systems.
3. Set the compressor regulator to a maximum of 50 PSI for PVC systems or 50 PSI for poly systems. Higher pressure can damage pipe and fittings.
4. Open each zone one at a time from the controller. Blow air through each zone until no more water comes from the heads (typically 2-3 minutes per zone). You will see the heads go from spraying water to spraying mist to blowing dry air.
5. Repeat the process a second time for each zone to ensure thorough drainage
6. Open manual drain valves at low points in the system
7. Disconnect the air compressor

Protecting Above-Ground Components

• Insulate the backflow preventer with a commercial insulation cover or wrap with pipe insulation and secure with tape
• Insulate any above-ground piping or valve boxes that are exposed to freezing temperatures
• Set the controller to "Rain" or "Off" mode (do not disconnect power if the controller has a backup battery that needs to stay charged)

Water Conservation Best Practices

Water is an increasingly expensive and regulated resource. Efficient irrigation is not just good for the environment - it is a business necessity.

• Design systems with matched precipitation rates on each zone
• Use rotary nozzles or drip where possible (lower application rates = less runoff and waste)
• Install rain sensors or soil moisture sensors on every system
• Program cycle-and-soak on slopes and clay soils
• Audit existing systems annually: check for head alignment, overspray, leaks, and proper scheduling
• Educate property owners and managers on seasonal scheduling adjustments

Key Takeaways

• Always call 811 before digging. No exceptions. It is the law and protects lives.
• Never mix sprinkler head types on the same zone. Matched precipitation rates are essential for uniform coverage.
• Program watering for early morning (4-6 AM) to minimize waste from wind and evaporation.
• Winterize the system before the first hard freeze in cold climates. Freeze damage is expensive and entirely preventable.
• Understand pressure and flow. Most irrigation problems trace back to a system that exceeds its available pressure or flow capacity.