A pressure-vacuum breaker is an important part of any irrigation system and is required by most cities because it prevents contamination of the potable water supply through the irrigation system. It works by breaking back-suction on the lines should water pressure fall, thereby preventing contamination from being drawn back into the water supply. You can call the local building code office to find out if it is required, but even if it is not required in your area, it is a good idea to install one. Installing a vacuum breaker yourself can save you money on the cost of installation.
Pressure-vacuum breaker installation can be easy, especially if you have a PVC main water line. Usually, you want the pressure-vacuum breaker fitting to be located close to the sprinkler valves and right after a stop-and-waste valve, especially if you live in a colder climate. This vacuum-breaker installation configuration will help drain the line down when you shut down the irrigation system for the winter.
How to Install a Vacuum-Pressure Breaker
- Dig up the area between the valves and the main sprinkler shut-off. If you do not have a shut-off valve here, it might be a good idea to install one. To install a pressure-vacuum breaker, you should not need more than 12" to 18" of space.
- Make sure the pressure-vacuum breaker valve is the same size as the pipe. Downsizing the pipe with a smaller valve can cause some water volume problems throughout the sprinkler system, as the water flow becomes restricted by the smaller pipe size.
- Get a parts list together. If you are doing the installation with PVC, the parts list should consist of something like this: three 90° elbows, two male adapters, pipe, glue, primer, plumber's tape and maybe unions, if you want to be able to replace the vacuum breaker easily in the future or to remove it for harsh winters.
- Apply plumber's tape to the adapters and screw them into the pressure-vacuum valve so you that can see exactly how much room you will need between the inlet and the outlet with a PVC 90° elbow pointing down from the outlet. If you have plenty of room to work with, the installation should be easy. If you have limited space, this step will help you figure out what you are dealing with. Have a plan before cutting the existing pipe for the installation.
- Mark the PVC main water line and cut it to fit your pressure-vacuum breaker valve. The valve needs to be at least 12" higher than the highest outlet, as measured from the center of the middle ball valve.
- Measure and cut the lengths of pipe necessary to install the vacuum breaker at the correct height. When cutting the PVC risers, leave them a little longer than necessary, since you can always cut them shorter later.
- Prime and glue the PVC 90° elbows onto the pipe in the ground first, with the pipe risers. Use a level to help ensure that the risers are positioned exactly plumb.
- Measure and install the unions. Measure the length of the small piece of pipe that will go between the pressure-vacuum breaker and the outlet 90° elbow. Cut and glue the pipe and 90° elbow to the PVB adapter.
- The final step is to glue the vertical pieces straight down into the fittings. Dry-fit the pieces first if it helps you line up and level the valve, but do not forget to glue the joints. This is why it is always a good idea to use the colorful glue, so you can tell which joints have glue and which do not. NOTE: Make sure to install the pressure vacuum breaker in the right direction. There should be a flow arrow on the PVB.
- Allow the joints dry for the amount of time noted on the glue that you used. Leave both valves off on the pressure vacuum breaker. Turn the main sprinkler valve on slowly, then turn on the PVB one valve at a time, unless instructed otherwise by the manufacturer. Check for leaks at the joints before backfilling.