Polyvinyl chloride, or PVC, is widely used in irrigation systems, both above-ground and buried. With many fittings regularly available, including slip, threaded, and push fit, the configuration options are endless.
Read on to learn more about what to consider when choosing pipe fittings for irrigation applications.
Pipe Schedule Considerations
Both schedule 40 and schedule 80 PVC piping are commonly used in irrigation systems. Gray in color to differentiate from schedule 40, schedule 80 has thicker walls, making it stronger. That design increases PSI, but can also restrict flow. It’s typically used in above ground systems. Schedule 40 PVC, on the other hand, is white with thinner walls. While it can handle heavy flow, it’s best used in drainage, irrigation, and cold-water applications. Schedule 40 piping is also lighter than its counterpart, making it less expensive and a bit easier to work with.
Fittings for PVC are measured the same way, in schedule 40 and schedule 80 options. You’ll notice that they will fit interchangeably, but it’s best to use the same schedule pipe and fitting. This will ensure a consistent strength throughout the irrigation system.
Important PVC Terminology to Know
You might see the connections for PVC fittings described as “SSS,” “ST,” “SST,” etc. The “S” stands for slip, socket, or spigot. These connections have no thread and are solvent welded, which means that a cement glue is applied to both the pipe and the fitting. The acetone in the cement glue allows the pipes to melt together, forming a very tight seal.
The “T” in these fitting configurations stands for “threaded.” In threaded fittings, the pipe is twisted to fit securely into the fitting. However, threaded joints need a sealer as well. The sealer lubricates the parts, making it easier to thread the pieces together. It also creates a stronger seal. Teflon tape is commonly used to seal threaded joints. It’s easy to use and less messy than other options. Pipe dope is often used as a sealer in other applications, but it has the consistency of a thick paste and could gum up the nozzles of the sprinklers in irrigation systems, so it’s not recommended.
PVC Fitting Types
Some common PVC fittings for irrigation systems include:
- Couplings: Small fittings used to join two pieces of PVC piping in a straight line.
- Male and female adapters: Allow users to connect two pipes with the same threading
- Caps: Used to stop the flow at the end of a pipe that does not need to be connected
- Plugs: Similar to caps; come in threaded and spigot versions
- Crosses: Used when joining four pipe sections or dividing flow in different directions
- Tees: Used when a line is split into two lines with a connection at a 90-degree angle.
- Side Outlets: Also known as “side elbows;” dividing flow in three different directions at right angles
- Push Fit: Metal barbs lock pipe into fitting; no solvent glue needed
Exposure to Sunlight
PVC piping is known for its strength, but it can become brittle when exposed to long periods of sunlight. This isn’t a problem for underground irrigation systems, but buried irrigation may not always be possible. In order to avoid exposure to sunlight in above-ground irrigation, you can apply several coats of an exterior latex paint or use foam pipe insulation. Both will help to block sunlight and avoid leaks or cracks caused by brittle pipes.
Below Ground Pipe Protection
In-ground irrigation systems should always be buried at least 10 inches deep. This depth could minimize the likelihood of being struck with a shovel or other tool, which could easily lead to cracking and breaking. Pipes that are not buried deep enough may also float to the surface in winter. In areas where temperatures consistently dip below freezing, you may want to consider using foam pipe insulation. Winterizing, where all water is flushed out of the system before the winter season, will also be necessary to avoid pipe breaks in the off-season.
Connecting PVC Fittings to an Irrigation System
It’s quite easy to install and connect PVC piping and fittings in irrigation systems. Before you get started, make sure to measure, keeping in mind that the pipe will slide all the way into the shoulder of the fitting once connected, which means you’ll need to measure the distance between the shoulders. Make the cut as clean and square as possible, removing any burrs that may be left inside the joint with a utility knife. Next, use a fine grit sandpaper to lightly scuff the end of the pipe and remove any caked-on dirt, then wipe away dust with a clean, dry cloth. Doing a dry-fit is important as well. Assemble all the pipes and fittings to be sure they are the correct length before cement glue or sealant is applied.
Instructions for Connecting Slip Fittings
When connecting slip fittings, don’t forget to prime. This temporarily softens a thin layer of PVC so that the cement glue can bond the two pieces together. Apply a layer of primer on the outside end of the pipe as well as the inside of the fitting. Then, brush the cement onto the end of the pipe and inside the fitting, making sure to cover all points of contact. Slide the pipe into the fitting until it meets the shoulder. Give the pipe a slight turn to evenly distribute the cement, and hold it firmly for 30 seconds to a minute until the cement cures.
Instructions for Connecting Threaded Fittings
Threaded fittings will also need a sealant. Before you choose one, check to make sure that it is compatible with PVC piping. Teflon tape is an easy and effective sealant for threaded PVC fittings. In the same direction as the threads, wrap male ends with three layers of tape, leaving the top thread empty. While it’s important to ensure that the pipe is securely in the fitting, be sure not to overtighten, as this could cause cracking or breakage.
PVC Push Fit Fittings: An Easy, Quick-Fix Option?
Push fit fittings are an optimal solution for many different applications. They can be used with copper and CPVC piping as well, but they are more commonly used in PVC irrigation systems. Push fit fittings are readily available at many hardware stores, and they are quick, easy, and much less messy than slip and threaded fittings. Glue is not required, so there’s no dry time. You can also use push fit fittings when pipes are wet, as long as they are clean, so systems won’t need to be shut down for extended periods of time.
Just because they are easy to use does not mean they are any less strong. Metal barbs inside the fitting grip the surface of the pipe once it is pushed in. Combined with a rubber O-ring, push fit fittings create a watertight seal that cannot be removed. The only way to remove a push fit fitting is to cut the PVC pipe, which means that dry-fitting your pieces before installation will not be possible. PSI and water temperature limits vary, so it’s always a good idea to consult the manufacturer’s specifications before purchase and installation.
PVC Fittings: Irrigation’s Solution
With so many options for PVC piping and fittings available, irrigation system configuration possibilities are endless. First, decide whether you should work with schedule 40 or schedule 80 pipes and fittings. Then, choose the fitting style, whether slip, threaded, or even push fit, and determine the types of fittings you need to get the job done. Don’t forget the primer, cement glue, or Teflon tape either. When installing above-ground systems, be sure to minimize exposure to the sun, either by applying several layers of exterior latex paint or using a foam insulation. Buried systems should be at least 10 inches below the surface and should be winterized in areas where the temperatures often dip below freezing. As always, check each manufacturer’s product specifications to ensure proper use.