By William Martin
An irrigation system is only as good as its original design and installation. Indeed, irrigation contractors can greatly minimize the incidence of future repairs by using proper installation techniques from the outset.
But even the best designs may still require repairs.
The goal of every irrigation system repair should be to restore the system to its original, or better, level of operation. Additionally, the contractor or repair technician should replace any item that has an above average probability of failing or malfunctioning within a relatively short period of time. Any repairs that are deemed appropriate and/or advisable but not immediately vital to the system, should be thoroughly discussed with customers before improvements are made.
GENERAL DIAGNOSIS.
Frequently, the customer, be it a homeowner or a commercial facility manager, does not understand how an irrigation system works, let alone what problem caused the irrigation system to function improperly. Therefore, one of the first challenges of repairing an irrigation system is diagnosing the problem. Ultimately, this involves the repair technician carefully inspecting the system and its components. Oftentimes, the technician can narrow down possible causes by first talking with the customer. A successful repair technician needs to learn to "read between the lines" of what a customer says and ask specific questions aimed at securing vital information.
For example, if the customer says, "Station Nos.1 and 4 don’t work," the problem is probably the field wires, solenoid or controller. More common scenarios include:
Customer: The last four stations do not work.
Likely Problem: Bad or cut common wire
Customer: My pump unit burned out and now the system doesn’t work at all.
Likely Problem: "Dead head;" bad section or master valve
Customer: My system was installed several years ago, and now I have a few dry spots in the yard.
Likely Problem: Possible clogged heads/nozzles or irrigation lines; drop in city main pressure
Customer: The spray heads barely pop up now.
Likely Problem: Wrong heads; dirt/debris in the head, nozzle or water line; broken fitting or riser; cross-threaded riser
Customer: We recently put in a fence and now the back yard is not being watered.
Likely Problem: Suspect a cut field wire.
Customer: We had a new roof put on last month. Now when the irrigation system turns on, there is a soggy spot in the front yard.
Likely Problem: Truck probably drove over a valve box, which pushed down and broke the valve outlet side and/or outlet pipe.
Customer: Water spurts out of several heads.
Likely Problem: Bad seals or nozzles.
DEALING WITH VALVES
There are two common problems with valves – they won’t close or they won’t open. When a valve will not close, the problem is usually due to a physical obstruction (sand, debris, etc.) that prevents the diaphragm from seating. A valve might also not close due to insufficient force above the diaphragm. This can be caused by a missing plunger or one stuck in the up position, a plugged diaphragm filter, a flow control that is turned up too high, constant voltage from the controller, a leak between the bonnet and the valve body or an open manual bleed.
Valve closure problems also can be due to a hole in the diaphragm (cracks or slits) caused by a build up of mineral deposits, resulting in a stiff rubber diaphragm.
If the valve turns off after the common wire is disconnected, the problem is controller-related. Test the controller, then repair or replace it as needed. If the valve seems to turn off, but water is still present at the low head, it is likely a seeping valve. This can be attributed to a leaking diaphragm, a partially clogged internal port, worn or damaged solenoid plunger, valve seat or mechanical defect. This may require replacement of the valve if the problem is not resolved after flushing and replacing the diaphragm.
When a valve will not open, the flow control might be turned all the way down, the solenoid might be burned out, valve ports might be plugged, or voltage from the controller might not be getting to the solenoids.
ELECTRICAL WOES
There are a variety of tests that can be performed on the electrical components of an irrigation system, including checking the condition of field wiring, ensuring the system is properly grounded, checking the transformer and troubleshooting controllers.
One of the most common checks is evaluating the condition of the field wiring and solenoid from the controller. To do so:
1. Disconnect the common wire from the controller.
2. Set the Volt-Ohm meter to "Ohms."
3. Connect one of the meter leads to the common wire.
4. Touch the second meter lead to each of the station terminals and record the resistance readings. (Compare readings to the 20 to 60 ohm base values of most solenoids).
5. If the ohm measurement is within the 20 to 60 ohm range, then the electrical circuit for that station is good.
6. If the ohm measurement is below 20 ohms (indicating a short), then check the valve solenoid for proper resistance and operation. Be sure to disconnect both field wires from the solenoid before performing this test.
7. Based on step 6, measure the ohms of the solenoid lead wires. If the resistance is less than 20 ohms, solenoid needs to be replaced. If the solenoid resistance is within the acceptable range, the short is in the field wiring. Note: If two solenoids are connected to a single station, the resistance will be less than the resistance for the "least resistive" solenoid. Use wire tracing equipment to locate the shorted field wiring.
PUMP PROBLEMS
The main factors to look for with a pumping system that is not working or producing enough water pressure include suction, electrical, control or relay problems or sectional valve problems.
The first thing to look at in diagnosing pump problems is the pump power and whether or not the power is appropriate for the type of pump being used.
Next, determine whether or not the pump system is running at all. If it is running, determine if the amount of water (volume) and pressure on the discharge side of the pump are adequate to run the system.
If there is a filter system in place, determine if the device is clogged with sand or other dirt, which can impede water flow.
UNIFORMITY CONCERNS
Perhaps the most obvious problems to spot are related to uniformity. For example, diagnosing a broken spray head with water dribbling, leaving turf or plant life in the area brown and parched, is easy. Replacing heads or nozzles usually solves such problems.
Other uniformity problems can be more challenging, such as an inadequate design or improper scheduling that requires a system audit and a plant and soil evaluation. Some other common uniformity problems include:
• Incorrect or inconsistent heads and nozzles
• Plant growth interference
• High pressure, requiring flow control devices and/or pressure regulators
• Low head drainage, requiring new heads with check valves
• Soil compaction, requiring aeration or dethatching of an area
The author is owner, Lone Star Irrigation Training, Poolville, Texas. This article is excerpted from his book, "Repairing Irrigation Systems."