If you want to design a drip irrigation system, then you are at the right place!
My name is Jeffrey Zimmerman, founder of Dripwerx Irrigation. I have been designing drip irrigation systems since I was 18 years old. Over the years I have formed a general process of steps I follow when I'm designing a drip irrigation system. Bear with me, as I lay out the process I follow when designing a drip irrigation system.
Shortcuts:
Step 1: Available Water Flow:
First I want to know how much water flow is available to feed the irrigation system. If the water source is a hydrant, or faucet, it can easily be tested using a 5 gallon bucket. Ideally there is a pressure gauge in the plumbing system that can be used to monitor the pressure while the water flow test is conducted. If you have a rural well, you first want to make sure you are not measuring the water flow while your pressure tank still has a reserve of water. You will need to open the faucet or hydrant all of the way & let it the water free flow for at least 5 minutes or until you hear the well pump start to run. (if you are on city water, skip this part) Now, restrict the flow to create back pressure by partially closing the faucet or hydrant until the pressure gauge maintains a stable 20 – 30 PSI. Using a 5 gallon bucket, (or other container that has a known volume in gallons) measure the time it takes for the bucket or container to completely fill with water. Divide the volume of gallons that the bucket or container holds by the amount of seconds it took to fill the bucket, & multiply by 60. This gives you your water flow in GPM (gallons per minute)
Example: You have a 5 gallon bucket to test your water flow. Using a timer, you see that it takes 30 seconds to completely fill the bucket. Using the formula we learned above, looks like this
5 / 30 x 60 = 10 GPM. We know know that we have a water flow of 10 GPM
Step 2: Amount of Drip Tape Needed: Now let's see how much drip tape we will need, Multiply the number of rows by the length of the rows to come up with the row feet of drip tape needed.
Step 3: Selecting The Correct Emitter Spacing: A successful drip irrigation system needs to be tailored to your soil type & variety of crop being irrigated. The soil type will influence the decision for drip tape's emitter spacing. If the soil is sandy & well drained, a 4” or 6” emitter spacing is generally chosen, It is also a common spacing to use inside of a greenhouse or high tunnel. If your soil is a lighter loamy type, 8” emitter spacing is a good fit. 12” emitter spacing is recommended for heavier loam, or clay soil.
In addition, if the tape is watering something like a bed of carrots where the plants are spaced less than a few inches apart, I generally default to a 4” or 6” emitter spacing, regardless of the soil type.
Step 4: Selecting The Correct Drip Tape
We will assume a drip tape diameter of 5/8” this is by far the most common diameter.
(Larger diameters, such as 7/8” are sometimes used in larger systems, typically 15+ acres.)
Since there is a lot that goes into choosing the correct drip tape. This step is broken down into 2 sections.
Step 4a:
We know what the drip tape emitter spacing needs to be from step 3, we now need select the correct wall thickness for our drip tape. If the drip tape is going to be used for a single season & then discarded, an 8 mil wall thickness is ideal, for rockier soil or overwintering, a 10 mill wall thickness is used, for multi season use, 12 or 15 mil is recommended, although 10 mil can also last for 2-3 seasons.
Step 4b:
Now we need to determine the correct drip tape flow rate, (flow rate is the term used to describe how much water the drip tape puts out, or in other words, how fast it waters.) The flow rate is typically measured in gallons per minute per 100' of tape. There are 2 things to factor in when choosing the correct flow rate. The 1st thing is the length of the longest rows. The 2nd thing is the terrain, If your rows are fairly level, or if they slope up or down hill.
The following guidelines apply if your field is level. If your field slopes downhill, you can run longer rows, if it slopes uphill, your row maximum length will be decreased.
For level rows under 200' long, virtually any flow rate can be used such as 1.34, or 1.0 GPM.
For level row length is up to 400' the highest flow rate will be .67 GPM.
For level rows 500-600' long, choose a flow rate of .5 GPM or less.
for level rows 500-800' long, choose a flow rate of .34 GPM or less.
For level rows 800-1,000' long choose a flow rate of .25 GPM or less.
Additionally if you have a hilly field & uneven elevation instead of level or steadily downhill sloping rows, a flow control, also named pressure compensating, drip tape is recommended. This type of drip tape will reduce over watering in low spots & light watering in high areas. Flow control tape also allows for slightly longer rows at the same flow rate compared to standard tape.
Step 5: Selecting The Correct Main & Transfer Lines.
A drip irrigation system needs a header pipe where all of the individual drip lines are connected to and a water supply line or transfer line that connects the water source to the header pipe, it is critical to select the correct type & diameter of pipe, tubing, or hose when designing a drip irrigation system. The header pipe is typically a soft polyethylene orchard tube, or oval hose. A barbed connector is installed into this tubing to make the connection to the drip tape.
If the water source is within 100' of the field, the low pressure header pipe can be connected directly to the water source, eliminating the need for a transfer line. If the water source is over 100' away, a higher pressure transfer line is typically used. When the transfer line is above ground, layflat is the most common & most economical choice. If the transfer line is buried, PVC pipe, or stiff, high pressure poly pipe is commonly used.
Once the proper header pipe and/or transfer line have been selected. We now need to select the correct diameter for these lines. Two factors are used to determine the correct diameter. Flow rate & distance. As water travels through a line or pipe, it encounters friction from the walls of the pipe. If the pipe diameter is too small for the amount of water being forced through the pipe, large amounts of pressure will be lost due to friction loss, this pressure loss adds up as the water travels which is why the length of the pipe or line needs to be factored in as well. I have listed a general guide you can use to select the correct pipe diameter if your piping won't be running more than several hundred feet. for longer runs, refer to the additional info & chart at the bottom of this step
1/2” tubing is used for flow rates less than 3 GPM,
3/4” tubing is used for flow rates between 3 & 7 GPM,
1” tubing is used for flow rates of 7-15 GPM,
1.5” tubing is used for flow rates of 15-40 GPM
2” tubing is used for flow rates of 30-80 GPM.
Another thing to consider when sizing our pipes, especially if we are going many hundreds or even thousands of feet, is we want to know how much excess pressure we can afford to lose between the water source & the headline feeding the drip lines, both through through friction loss & elevation. In most cases you need a minimum of about 15 PSI at the head line feeding the drip tape. We deduct the minimum pressure from the pressure at the water source which is typically between 30 – 60 PSI. We then deduct the pressure loss due to elevation. For each 2.31' of elevation rise or fall, the water pressure will drop or increase by 1 PSI. For instance, if the field being irrigated is 20' above the water source, you will lose 8.6 PSI. The remaining difference between the source pressure & the needed pressure at the head line is excess pressure that can be sacrificed in the transfer line through friction loss. Calculate the friction loss using the table further down, or refer to your specific pipe or tubing's specifications. The following example should help explain this.
We have a water source that Provides 12 GPM @ 40 PSI.
The field being irrigated is 400' away from the water source & requires 12 GPM at 15 PSI.
The field is also 20' higher than the water source. which means that we will lose about 9 PSI due to gravity.
The 400' long Transfer line is a 1” layflat hose, the water flowing through it at 12 GPM will lose about 3.5 PSI for every 100' it travels, which means we lose about 14 PSI due to friction loss.
In summary, we start with 12 GPM @ 40 PSI, we lose 9 PSI due to elevation gain, and 14 PSI due to friction loss. By the time the water reaches the header pipe supplying the drip tape, it is at 12 GPM with 17 PSI.
Step 6: Zoning
Now we'll need to figure out how much water flow would be required to run every row in our drip irrigation system at once. For example, let's say we have 25 rows at 400' long for a total row footage of 10,000' The tape we are using has a flow rate of .5 GPM per 100' so we divide the row footage by 100 & then multiply that number by the flow rate of the drip tape.
(10,000 / 100 x 0.5 = 50 GPM ) The flow needed to supply all 10,000 row feet is 50 GPM. Now, let's say our water supply only has a flow rate of 12 GPM at 30 PSI. That means we can only run about 1/5 of the rows at once. We can either have a single header pipe (usually oval hose or orchard tubing) & have a shut off valve for each drip tape line, or we can run a main line that supplies 5 sub-main header lines, with a valve for each sub main connection (zone).
Step 7: Pressure Regulator, Fertilizer Injector, Filtration, Check Valve, Etc:
We have now selected our drip tape, supply lines & header lines. Lastly you need to source various fittings to connect everything together! I have listed the most important components in this final step.
Pressure regulator: Standard drip tape is designed to operate at pressures of less than 20 PSI, ideally between 8 and15 PSI. A pressure regulator is typically installed at the beginning of the header pipe or sub-main line to protect the drip tape from over-pressure.
A fertilizer injector is also commonly used to inject water soluble fertilizer or chemicals into the irrigation water. The most common fertilizer injector is a venturi type injector. It is essentially a water powered siphon that operates by creating a slight drop in the water pressure. This type works best if installed at the beginning of the main line or head line. Another type, is a proportional injector, it can be installed at any point in the system.
Filtration: All drip irrigation systems need a filter, most drip tape requires a filter's screen size to be 120 mesh or finer. (the higher the number the finer the screen) 150 mesh filters are commonly used. For well or city water, a screen filter is normally sufficient, for river or lake water, a disc filter, or sand filter is usually necessary to accommodate the higher volume of debris in the water.
Back flow prevention: A back flow prevention device or check valve also needs to be installed, it is usually installed onto the outlet of the water source to avoid potentially unsafe water to be forced back into your water source.
Conclusion:
Hopefully after reading this post you now have the confidence & resources to start planning & designing your system! You can check out our blog for other helpful resources.
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Would you rather have a professional handle the designing & component selection? Dripwerx Irrigation can design the perfect system for you! You can give us a free call at 641 207-0705 to see how we can help. You can also email us at info@dripwerxllc.com or book directly through our website.