IRRIGATION
the gallons per minute required for your largest zone in the system, Gurzler says. Oftentimes, irrigation plans for new construction are based on the water capacity that the designer anticipates will be available on-site. In those cases, the notes will often include the caveat that a pump may be required to meet design specifications. “Based on your irrigation system design, you’re looking
to meet the pressure requirements after friction loss has been calculated to get your sprinklers or drip irrigation to the desired pressure,” Gurzler says. Generally, contractors will first install a system as the
plans are laid out to determine whether its performance is what it was intended to be. Ten they will make the de- cision to add a pump if the output doesn’t match up to the original expectations. Gurzler says that considering the system flow up front saves time and effort. “You should flow test and pressure test before installa-
tion so you know right away if you need a pump,” he says. Tere are a couple different options for determining a
system’s water capacity. According to Gurzler, one option is attaching a flow meter to the pipe, opening the pipe and measuring the flow. Another option is the tried-and-true bucket test. “You would do that with a stopwatch and a bucket or
collection vessel to see how many gallons a minute you have coming out of the pipe,” he says.
RIGHT FOR THE JOB
Having the proper test equipment and tools at the ready makes service easy to perform.
Pump sizing is based on the specifications set forth in the plan design. If a system design calls for sprinkler heads to operate at 70 psi but it is actually operating at 55 psi, the system needs 15 pounds of boost from a pump. Tis is of- ten a point of misconception in the industry, Gurzler says. When sizing for a pump, it’s easy to think that because the system needs 70 psi of output, the contractor should just ask the distributor for a 70-psi pump. In the above exam- ple, that would be oversizing the pump because it doesn’t take into account the system’s current output. “You need to know the incoming pressure and the out-
KNOW YOUR FLOW
Te main purpose of a pump in an irrigation system is to either create pressure from nothing or to boost pressure. A system with low pressure will perform poorly, while a system with too much pressure will be inefficient. “If pressure is too low, the sprinkler head won’t be able
to throw the designed distance, so coverage will be bad,” says Jim Gurzler, CIC, of Reasonable Outdoors in Drums, Pennsylvania. “If the pressure is too high, you’ll see misting from the sprinkler heads, which means your droplet size is too small and you’ll have a lot of drift and potential for waste.” In cases where the water is coming from a natural source like a lake or a cistern, using a pump to create pressure is a no-brainer. But most often, a contractor will need to take stock of the water capacity and pressure that’s available, then make a determination. Te maximum gallons per minute required to efficiently operate an irrigation system is based on the pressure and
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going pressure, then determine the gap,” he says. Oversizing the pump has a few negative ramifications.
First, you’ve spent too much on a pump too big for the job. Second, you could be overpressurizing the system, result- ing in wasteful mist. But too much pressure is more than wasteful. It can also wreak havoc on the system’s compo- nents. “If you oversize the pump, the pump is trying to draw
too much water into the pipe, which can create cavitation that can damage the pump,” Gurzler says. Once you select a pump with the right boost and the
right gallons per minute, it’s time to select the right motor. A 115- or 240-volt single-phase power supply is the
right choice for residential installations, while a commer- cial job site might have a 230-volt or 460-volt three-phase power supply. In some cases, a designer may have planned for a three-phase power supply that doesn’t exist on a job site. In that case, a variable frequency drive can transform a single-phase power supply into a three-phase power supply. “Some commercial sites don’t have a three-phase power source. In that case, you can buy a variable frequency drive
Late Fall 2022 Irrigation & Lighting 23
YOU SHOULD FLOW TEST AND PRESSURE TEST BEFORE INSTALLATION SO YOU KNOW RIGHT AWAY IF YOU NEED A
PUMP.” – Jim Gurzler, CIC, Reasonable Outdoors
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