Fittings – especially irrigation fittings – are not very exciting, but they are important. The industry talks about pipe life expectancy, but rarely does the pipe wear out. It’s the fittings that wear out or cause the most issues. If it is not the fitting itself, it’s the joining mechanism/process used to connect the fitting and the pipe. Fitting failure is non-discriminant. It doesn’t matter whether it’s PVC of HDPE.
In the old days, there wasn’t a lot of selection in the fitting type used on a golf course irrigation system. PVC started with solvent-weld cement fittings and these either came apart or cracked. This progressed to gasketed PVC fittings (they cracked, too, just not as quickly) then to the disaster that was epoxy steel fittings in the mid-80s and finally on to ductile iron fittings, which is standard on PVC piping systems. We are seeing some stainless steel also, but more on the valve side than the fitting side.
HDPE doesn’t quite have the history, but there are many choices with HDPE and the type fitting best used on golf irrigation systems is still being sorted out. HDPE fittings include molded, fabricated, electric fusion, strap saddles, tap saddles and compression. Different designers prefer different types and in some cases different pressure ratings. Many times the type fitting used (for PVC or HPDE pipe), is based on the size of the pipe and therefore the fitting required for the pipes application. Mainlines usually use different fittings than lateral pipes, but not always – the same material can be used, but smaller sizes.
Fittings fail for many reasons. One is they absorb most of the force of the water flowing through the pipe. Water is heavy and when running at speed creates strong forces (force = mass x acceleration). The fact that we like to turn large amounts of sprinklers (flow) on and off at the same time (acceleration = change in velocity divided by time) causes surges we expect the fittings to absorb. Sometimes the fitting doesn’t absorb the force at all or no longer can absorb the force due to the repetitive schedule of irrigation systems and the fitting breaks. The other issue is installation. With both PVC and HDPE, poor installations show up quickly, average installations show up in 10 to 12 years and good installations in 15 to 17 years and excellent installations may last 25 years or more. Time always catches up to the fitting. As your irrigation system goes through on/off cycles, the fittings flex pretty much every time the system goes on or off and when the flow amount or direction changes. So fittings wear out with time – just like a pump station, a valve and/or a sprinkler. The pipe may have years of life left, but the fittings render it useless.
So which is best? It depends on your budget and how much repair work you want to perform. It also depends on whether you want to perform that work with your crew or contract it out. Certain fittings work better in certain situations. As with everything, better fittings cost more money, but the money spent is well worth it. For example, you can spend the least amount of money by buying solvent-weld cement fittings for PVC, but they do not work well on 3-inch-plus pipes because applying the cement becomes more difficult with size. Spend more money and use gasketed fittings, but they won’t last the life of the system and most likely will start failing before the sprinklers. You can use ductile iron fittings – much more money, but with lots more strength and longevity (50-plus years). With HDPE you can use saddles on both mainlines and laterals or spend more and use molded fittings on the mainlines and compression fittings on the laterals.
All fittings on PVC systems and some HDPE need to be restrained. This is accomplished with joint restraints, thrust blocking or a combination of the two. Most PVC systems are still done with thrust blocks as opposed to joint restraint.
Fitting discussions are not exciting, but they play an important role. Chasing and repairing fitting failures is a miserable job. Spend the money to purchase strong, long-lasting fittings and hire an installer who knows what they are doing, especially with the larger pipe sizes and pressures encountered in golf irrigation systems.