PVC Pipe Fittings For Irrigation

Poly vinyl chloride (PVC) pipe is the preferred material in the landscape irrigation industry today because of its strength-to-weight ratio, durability, ease of installation and resistance to chemicals. However, a simple score, dent or hairline fracture on the pipe, sloppy solvent or cement applications, poor trenching and backfill conditions and other installation problems can lead to a piping failure that can ravage a landscape in a matter of minutes.

SLIP-BY-SLIP RULES. When properly welded, PVC joints can be stronger than the pipe itself. Primer and cement are intended to first dissolve the surfaces of the male and female ends, then, as the solvent evaporates, merge them. Because the solvent, or primer, is intended to break down the material, care should be exercised during application.

Your trench is dug and free of rocks and garbage, and you're ready to begin connecting pipe and fittings (2-inch or smaller). Check that the pipe is dry and that, with a cloth or gloved hand, you have cleaned both surfaces before applying primer. If there are any rough edges or burrs from a (clean and straight) cut, smooth the area.

Carefully apply your primer, then your cement, ensuring that both completely cover the area to be fused, but don't run halfway up the length of the pipe. Bare spots left after applying cement will compromise the welded joint. Splice the pieces together while the cement is still wet, within about 15 seconds of application, then give the pipe a quarter-turn while pushing the male end into the bell housing, or socket. This evens the distribution of cement. Ensure that the male end of the pipe reaches the end of the socket, and don't turn the pipe once it has reached the end.

Hold the splice together for about minute to keep the male end from backing out of the socket. Allow ample time for the connection to cure before handling, burying and charging the line.

TWISTS OF FATE. Threaded PVC is another area that requires attention. The tendency when connecting threaded PVC pipe is to torque down on the joint, and that's easy to do as the threads are much smoother and thread sealant can have a lubricating effect. Over tightening is the single greatest cause of failure in female threaded PVC.

The thread taper, amount and type of sealant, temperature and size of the fitting all factor into the amount of torque to apply when assembling threaded PVC. The best judge of how far to tighten a threaded PVC joint is to finger-tighten (not hand-tighten) the joint, then give it one or two additional full turns. For 2-inch or smaller PVC fittings, a pipe wrench isn't necessary.

Thread sealant and Teflon tape both are effective in securing the joint - just follow manufacturers' recommendations. If you elect to use a paste sealer, check that it is suitable for PVC. Standard pipe dope and other liquid products are not compatible with PVC and should not be used. Swing joints or other fittings that require movement warrant a higher-viscosity sealant.

Teflon tape can be difficult to work with until you develop your technique. When wrapping Teflon tape around the male fitting (clockwise for standard fittings), prevent the tape from spiraling on the threads and make the application as uniform as possible. Multiple wraps might be needed with some Teflon tapes, so ensure that there are no thick and thin areas on the thread that can cause additional stress on the fitting.

Do not let Teflon tape hang over the end of the male fitting, as it can break free and plug a valve or screen. Ensure that the fittings thread together smoothly and don't seize or lock up. Teflon tape should always maintain its integrity during the tightening process and not shred or peel.

JOINT VENTURES. Poly vinyl chloride pipe's strength certainly doesn't make it invincible. Added support at stress points, or thrust blocking, can secure years of life and performance to PVC fittings. Any place in the piping system where there is a change in size or direction has specific thrust forces exerted on PVC fittings. For example, at 100 psi, a 2-inch elbow can experience 500 pounds of thrust.

The design of effective thrust blocks is based on the amount of thrust generated and the bearing strength of the soil. Garbage on the site, rocks, bricks or four-by-fours are not effective thrust blocks and in fact can create uneven support and result in point stress on fittings.

To be effective, a thrust block should be placed against undisturbed or fully compacted soil, hug the fitting over a sufficiently large area to avoid point stresses and have adequate area on the soil side to support the joint without exceeding the bearing strength of the soil. Thrust blocking is a much neglected area in the installation of PVC pipe systems. Proper installation is but a single component of the performance and endurance of a PVC system. Efficient design and management of irrigation systems also determine the endurance of a pipe system. Although PVC has outstanding qualities that have helped to advance the irrigation industry, negligence in any of the three areas can result in premature failure of the system, of which the results can be devastating to the landscape.