A system isn’t ‘smart’ if its fundamentals are not sound

April 2, 2012  - By

By: Jeffrey Knight

It is incredible how far technology has advanced in the irrigation industry. There are soil moisture sensors that will tell you when the “plant available water” is depleted to an unacceptable level, just like the sensors in your vehicle’s gas tank. Flow sensors will alert you when you have a broken main or lateral irrigation line, or broken heads. Weather stations monitor the onsite evapotranspiration (ET) rates of the landscapes. Smart timers integrate all of this technology to drive water-efficient irrigation schedules.

However, none of these advancements mean anything if irrigation fundamentals are not practiced. I am talking about “Irrigation 101” type stuff.

A poorly designed and poorly installed irrigation system cannot be remedied by installing these types of products.

Pressure problems
Irrigation systems will always require a minimum amount of pressure to operate. Pressure is created by pumps, or by gravity. That’s it.

The smartest irrigation timer will never increase your static pressure. Fewer sprinklers on an irrigation zone will never increase your static pressure. Decreasing the flow by using fewer heads will reduce the pressure loss when the system is operating (dynamic), but if the static pressure is not high enough to begin with, it will not work properly. Using smaller pipe in the irrigation system will not increase water pressure.

This is one of the biggest misconceptions for beginning irrigators. As a matter of fact, the dynamic pressure loss is greater in smaller pipes. Without going into a long, drawn-out hydraulic explanation, let me just ask this: if it was possible to increase dynamic pressure by using smaller pipes, wouldn’t the fire department use 1/4-in. tubing to fight fires? Ridiculous, right?!

When the static pressure is excessive, the spray pattern of the heads will become distorted, and the flow rate through the sprinkler’s nozzle increases. This is a bad combination, because the uniformity — how evenly the water is applied — of the irrigation system decreases, and in most cases, the run times must be increased. The system is using a lot of water in a very inefficient way.

In most cases, a pressure regulator will fix this. Keep in mind that a typical regulator will lose 10 to 15 psi under normal flow situations, so make sure you really need one before you install it.  Many irrigation technicians install pressure regulators on ALL drip irrigation systems. Most emitters require 30 psi for them to operate properly. At times, the normal pressure losses through the irrigation system will cause a reduction in pressure to the required 30 psi without the use of a regulator.

Spacing shenanigans
Head spacing — the distance from sprinkler to sprinkler in an irrigation system — is another irrigation fundamental. The rule of thumb is to space the sprinklers “head-to-head,” meaning that the “distance of throw” (the reach) of water from one sprinkler will reach the adjacent sprinkler, and vice versa — providing for more even coverage. The use of head-to-head spacing is a standard practice, and a pretty good rule to live by.

Here’s another good rule: It is always better to slightly compress the heads, than to stretch them. The distribution of water is not uniform throughout the head’s radius. Most of the water lands closest to the head, and then decreases as you move outward. Spacing the heads so the water from one head lands on the adjacent head improves the uniformity of the system.

Know your hydrozones
I cannot overstate how important it is to separate the irrigation stations so that the sprinklers within the station are watering the same type of vegetation, in the same microclimate. Flowerbeds and turfgrass should be separated. Areas of full sun exposure should be separated from areas of shade. Most importantly, spray heads should be separated from rotary heads. (You would be surprised how often I see this disaster occurring in the field.)

All of the intelligence of a “smart” timer is wasted when the system is set up to irrigate landscaping that has different watering requirements.

I encourage you to investigate and make use of the technology and advancements that are at your fingertips, but before you invest in these upgrades, make sure the fundamentals of your
irrigation system are sound.

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AT Staff

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