Irrigation 101


Plumbing codes require a backflow preventer on many systems, including all irrigation systems attached to a drinking (potable) water supply. A backflow preventer blocks water beyond the point of connection from getting back into the potable water supply. The backflow preventer is installed near the point of connection. The point of connection is where the irrigation system is hooked into the municipal water supply.

For most irrigation systems, you will need a reduced-pressure-type device or pressure vacuum breaker. In some circumstances, an atmospheric vacuum breaker may be allowed and, on occasion, a water authority may require a double-check-type backflow preventer. However, under the National Plumbing Code, double-check valves are not allowed for irrigation use.

In order to irrigate, you need some type of emission device to apply water to the landscape. Conventional turf and landscape systems use sprinklers, although there are other types of devices available such as drip or in-line. There are thousands of different sprinklers manufactured by many different companies for use in an irrigation system. These can be categorized into general groups: bubblers, spray sprinklers and rotary sprinklers. Rotary sprinklers can be further divided into categories based on their use: residential and commercial, athletic field and golf. For this discussion, we will talk about spray sprinklers and small and medium rotors for use on residential or small commercial properties.

Types of sprinklers

Spray sprinklers are fixed arc sprinklers that throw in a spray or fan-type pattern. They have pop-up heights of 2, 4, 6 and 12 inches as well as a few others. The pop-up you select is based on what you are watering and how much clearance you need. For example, spray sprinklers in turf would normally have a 4-inch pop-up height. Spray sprinklers are available from all of the major manufacturers. They throw a maximum radius of 17 feet at a pressure of 20 to 30 psi. Water use will vary with the nozzle selected, but will commonly be in the 1- to 4-gpm range.

Rotary sprinklers are generally single-stream sprinklers that rotate. The sprinkler can be full-circle (360 degrees) or an adjustable part-circle where the degree of arc can be set. Gear-driven rotary sprinklers turn the sprinklers through a gear train with a consistent rotation speed. Impact rotary sprinklers turn due to the arm moving the sprinkler along its arc. Rotary sprinklers are available in many sizes. A small rotary sprinkler throws a distance of 18 to 30 feet operating at pressures from 25 to 40 psi. Water use is 0.50 gpm to 3 gpm, but will depend on the nozzle. Medium rotary sprinklers throw water 30 to 50 feet at pressures ranging from 35 to 60 psi. Water use can be as low as 1 gpm and as high as 14 gpm. Pop-up heights for rotary sprinklers vary, but are generally 3 to 5 inches. You also can purchase selected manufacturers' rotors with up to a 12-inch pop-up height.

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