Pieces & parts

Understanding the functions of irrigation systems’ crucial components can help prevent system breakdowns.

To choose the right valve for a job, contractors must assess the quality and dynamic conditions of the water supply.
Photo courtesy of Hunter Industries Incorporated

When an irrigation system fails, it’s important to understand the mechanics behind the system.

“If a contractor really understands what makes a valve come on, they can then understand what possible causes of a malfunction might be and may be able to more quickly troubleshoot and fix a valve,” says Rain Bird Product Manager Ron Wolfarth.


An important part of an irrigation system, valves turn the water on and off in response to a signal from a controller, says Hunter Product Manager Steve Hoveln.

“Valves are the one thing that controls everything else downstream. If your valve leaks or doesn’t turn off or on, it can affect a huge portion of your landscape because it controls a larger zone of spray heads or rotors,” Hoveln says.

The valve is made up of three main elements: the body, the diaphragm and the solenoid. The body is where water enters and exits the valve. Water flows in the inlet, above the diaphragm and up into the solenoid. It’s held there by the solenoid plunger until a controller sends an electric signal.

When that happens, the solenoid coil becomes an electromagnet and pulls the plunger up, allowing water to flow out of the valve.

This also raises the diaphragm, which is a circular piece of rubber that rises and lowers based on water pressure above or below it. When the valve is open, water pushes the diaphragm up and off the inlet.

When the signal is turned off, the plunger drops inside the solenoid and the water pressure above the diaphragm eventually offsets the pressure below it to close the valve. Valves vary in materials, pressure ratings and configurations. The most common type of valve is a globe style, where the inlet and outlet are in a horizontal line. Other styles include angle valves where the water enters from the bottom and exits at 90 degrees, which are popular in areas where the ground freezes, and a globe angle valve, which can be configured either way, Wolfarth says. To choose the right valve for a job, contractors must assess the quality and dynamic conditions of the water supply.

Valves are built in different sizes for different flow rate ranges. If the application’s needs fall below the chosen valve’s operational range, the valve may not close, Hoveln says.


In the same way as valves, irrigation pumps are sized based on both the flow rate and pressure of the water coming out of the source pipeline. If a contractor overestimates, the pump will not be matched to the actual needs and can destroy itself, says Rain Bird Product Manager Bill Beard.

“Pumps are what I call a dumb device; they are guaranteed to work or die trying. The amount of pressure and the flow required in the system dictates if the pump will operate, it’s never vice versa,” Beard says.

The most common type of irrigation pump is an end suction top discharge centrifugal pump. These pumps rely on centrifugal force to move water and a motor shaft to support the impeller. They have few moving parts and are easy to service, but for more boost, they must get larger and heavier.

In those cases, a vertical multistage centrifugal pump is more efficient because it has more impellers and can boost more pressure.

Serviceability and reliability of pumps and valves are the other important factors for contractors to consider when making purchasing decisions. The fewer parts it has, the easier it is to repair a product, Wolfarth says.

Contractors should work with the landscape designer to understand how much flow and what pressure is required at the point of highest demand on a job site, Beard says.

“The pump is designed to fill the gap between what is available for flow and pressure and what is required at the worst case scenario,” he says. “That rotor or spray body that’s the farthest away from the pump and the farthest uphill is the worst-case scenario. If you can't feed that particular device, you won’t be able to irrigate effectively.”

The author is a freelance writer based in Kentucky.

March 2017
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