Sprinkler System Main Line Leaks

Possible Causes

• Leaks in the main line of a sprinkler system are one of two general types. If the leak is at a joint between pipes or fittings, it is likely a result of improper installation. A specific procedure has to be followed when gluing PVC pipe in order for it to be fail-safe, including the way the pipe is cleaned and primed and how long the glue cures before the line is pressurized. If the the leak originates anywhere else, it is most likely the result of damage that occurred after the pipe was installed. If the pipe is not buried deep enough, it is easy to hit in the process of any number of landscaping, gardening or home-repair activities.

Confirming the Leak

• If the water bill is abnormally high, a stroll the yard to look for wet spots is in order. A small leak in well-drained soil may not be obvious on the surface, however. Making sure all the water taps in the house are off and checking to see if the water meter for the property is still turning is a good way to confirm if there's a leaky pipe. Once the general area of the leak is determined, the only way to find the source is to expose the pipe -- the leak will be in the area of wettest soil. If the pipe is cleaned and dried after the leaky area has been exposed, the leak should be immediately apparent by the reappearance of a bead of water on the pipe.

How to Fix It

• Modest home irrigation systems generally use 3/4-inch pipe for the main line, though larger systems may use a 1-inch or larger pipe. To make things easier when repairing the leak, use a telescoping coupler the same size as the pipe. Remove a section of the pipe containing the leak that is slightly longer than the length of the coupler when it is fully retracted. Prime all the surfaces that will be glued to clean them and assure a strong bond and follow all the instructions on the can of cement carefully. Apply the cement quickly to the surfaces and pull out the expandable side of the telescoping fitting until both ends of the pipe are seated snugly inside the corresponding receptacles of the coupler.

An Alternative Solution

• Finding a small leak in the main sprinkler line can be extremely difficult if the water is not apparent on the surface. In this case, an alternative option is to install a master valve where the main sprinkler line ties into the water supply. The idea is for this valve to come on only when the system is in use, which means the main line will only be pressurized for the limited times each week that the sprinklers are running. The master valve has to be wired to the control box for this to work, but most sprinkler controllers are designed to accommodate this. The terminal for the master valve wire is usually marked "MV" or "P," as it is also used to switch on a pump in irrigation systems that draw water from a tank or other body of water.