Drip Irrigation

Why use Drip Irrigation?

  • It's the most efficient method of irrigating. While sprinkler systems are around 75-85% efficient, drip systems typically are 90% or higher!

  • Much less wasted water! Drip is the preferred method of irrigation in the desert regions of the United States.

  • Concentrates the water at the base of the plant, where they need it most.

  • Reduces topsoil erosion.

Benefits

  • Water the plants you want to grow, not the weeds!

  • Easy to install and design

  • Can be very inexpensive

  • Can reduce disease problems associated with moisture on some plants.

How does it work?

Drip irrigation (sometimes called trickle irrigation) works by applying water slowly, directly to the soil. The high efficiency of drip irrigation results from two primary factors:

  1. Water soaks into the soil before it can evaporate or run off.

  2. Water is only applied where it is needed, (at the plant's roots) rather than being sprayed everywhere.

Installation

While drip systems are simple and pretty forgiving of errors in design and installation, there are some guidelines that if followed, will make for a much better drip system. These will hopefully increase the benefits of your new drip system, while steering you away from some common misconceptions and practices that can cause trouble.

Basic Parts Required to Set Up A Drip System

1 pressure reducer (10 p.s.i. w/ garden hose settings)
1 filter - 150 mesh, stainless steel screen (w/ garden hose fittings)
1 hose swivel
1 sub-main "T"
1 sub-main end caps
10 supply tubes (to connect the sub-main to drip tapes)
1 installation punch
1 installation shield
4 goof plugs
2 soil staples
installation instructions and assembly diagrams
drip tape, available in 100 foot rolls, T-5/8" with 4" emitter spacing
sub-main w/ coupler, available in 25 foot rolls, .62" i.d. x .71" o.d.
extra supply tubes, in bundles of 10 (if needed)

Typical Garden Layout

Layout of typical system

Material Descriptions

Drip emitters - what controls how fast the water drips out onto the soil. Most emitters are small plastic devices that either screw or snap onto a drip tube or pipe. Some models are preassembled as part of a tube. The most common emitters sold emit 4 liters/hour (4,0 l/hr) of water. That's about 1 gallon per hour (1 gph). There are many different types and brands available; they each have advantages and disadvantages.

Use pressure compensating emitters if you have an elevation difference of over 1.5 meters (5 feet) in the area you are irrigating. For more level areas turbulent flow emitters will work great and are often less expensive.

For most soil types 2.0 l/hr (0.6 gph) emitters work well and are more economical. For sandy soil use 4.0 l/hr (1 gph) emitters.

Diaphram emitters and Adjustable flow emitters.

Backflow preventer - drip emitters rest directly on the soil so it is especially important to have a backflow preventer to prevent water contamination by soil-borne disease. There are several types that will work depending on your situation and local codes.

Drip Tubing (Drip Hose or Drip Pipe) - a special tube used in most drip systems. The tube is laid on the ground surface between the plants. The emitters are installed on this drip tube. Drip tubing is a thin-wall polyethylene tube (thinner than standard polyethylene hose), has a low pressure rating, and is generally produced in metric sizes.

Common sizes are 12 mm (0.455" or 3/8"), 16mm (0.620" or 1/2"), 18mm (0.720" or
1/2"), and 24mm (0.940" or 3/4"). Do you see the problem? Two sizes are commonly referred to as "1/2 inch" in the USA!

  • Note: The fittings for these two are not interchangeable. So make sure you know what you're getting when you buy it! Do not bury drip tubing underground- gophers and moles love to chew on buried drip tubing! Some drip systems do not use drip tubing.

Spaghetti, Feeder, and/or Distribution Tubing - all names used for small diameter poly or vinyl tubes, anything less than 10mm (3/8 inch) in diameter.
I like to eat spaghetti, but I hate it in drip systems! The problem with these small
tubes is with maintenance. These little tubes tend to be easily cut, broken, pulled
loose, etc. and are generally a nuisance. This small tube is often connected to the
outlets of multiple-outlet emitters. This tubing is the reason I do not recommend the use of multiple-outlet emitters. There are a couple of exceptions where the tubes work well. One is when they are stapled above ground to a trellis or arbor for watering hanging plants. They need to be firmly attached, in a location where they will not be damaged. The other is for risers used on hard-piped drip systems.

  • Note: If you are a meticulous type person who can be very careful, do your own yard maintenance, and you don't have pets or kids in the yard, it might work for you.

Dripline (dripperline) - a drip tube with factory preinstalled emitters on it. Often the emitters are actually molded inside the tubing and all that is visible on the
outside is a hole for the water to come out. The emitters are typically the tortuous-path or diaphragm type, but may be other types as well. The emitters are uniformly spaced along the tube, often several different spacing options are available.

The primary advantage of dripline is ease of installation due to the preinstalled emitters. It is often used in agriculture; works well when you want to create a solid band of watered soil, such as watering groundcover beds, veggie gardens or lawn.

Drip Tube Fittings - (including tees, couplings, ells, and adapters) are the plastic
connectors used to attach the drip tube to other tubes, to control valves, or to pipes.

  • Note: Make sure the fittings are the exact right size! Using fittings made for a different tubing size will result in the tube blowing out of the fitting. 9 times out of 10, when a tube blows out of a fitting it is because the fitting is the wrong size. If you use a 15mm fitting on 16mm pipe you are going to have problems. Remember, both 15mm and 16mm tubes are often labeled as 1/2 inch size in the USA!

Barb type fittings insert into the drip tube. Generally they should not require the use of a hose clamp to hold them on, if a clamp is needed the water pressure is too high or the fitting is the wrong size. The advantage of barb fitting is that they are generally easier to install than the compression type. The disadvantage of the barb type is that as the tube goes over the barb it is stretched, which weakens the tube. The weakened tube will sometimes split open at the barb after a few years, especially if exposed to sunlight.

Okay you ask, if barbs are a problem then why do they use barbed fittings with standard polyethylene pipe? Standard poly pipe has a much thicker wall than drip tube and doesn't stress as much when stretched. You also clamp standard poly pipe to the fittings, which helps keep the pipe from splitting (that's why you need to clamp poly pipe even if it seems to stay in place without the clamps). Drip tubing is not clamped to the fittings (clamping doesn't help prevent splitting because of the thin drip tubing wall).

Compression type fittings are basically the reverse of a barb fitting. The tube slides inside the fitting, where an internal barb compresses the tube and holds it in place. The advantage of compression fittings is that they do not stretch the tubing, so they are not a cause of premature failure of the tube. Once the tubing is inside a compression type fitting it is very difficult to remove.

Control Valves - turn on and off the water to individual "circuits" or areas of the yard that are irrigated separate from one another. The control valves can be automatic (usually electric-powered using a solenoid) or manually operated (hand-powered, ie; turn, turn, turn!) There may be just one control valve or there may be several control valves on a drip irrigation system.

For example, one control valve may turn on and off the water to emitters/drippers in a vegetable garden. Another control valve might turn on and off the water to emitters for some hanging pots on a patio. Another control valve might turn on and off the water for the emitters at shrubs around the house. Another could even turn on and off water for sprinklers in the lawn, or water for filling the swimming pool or pond.

Pressure reducers (pressure regulator) - reduces the water pressure and keeps it at a constant level. Most drip systems operate best at lower water pressures than are common in a typical water supply system. A pressure regulator is used to lower the pressure and then keep it at that pressure, even if the incoming water pressure varies up and down. You probably will need to install a pressure regulator on your drip system if your water pressure is higher than 2.8 bars (40 PSI).

  • Note: Keep in mind that a pressure regulator only reduces the water pressure. It will never increase the water pressure, so if you don't have enough water pressure a pressure regulator will cause you to have even less!

Inexpensive, non-adjustable-type pressure regulators are most often used for
simple home drip systems. They are typically made of plastic and have a pre-set
outlet pressure. They often have very specific flow ranges and will not work if used at flows higher or lower than the listed range. Since they are not adjustable, be sure to buy the correct one for the flow and pressure your drip system needs.

The non-adjustable-type regulators must be installed AFTER the control valve, so if you have more than one control valve you will also need one regulator for each of the control valves. If a valve is installed after a non-adjustable-type pressure regulator it can result in a pressure surge that can damage your drip system. It has been my experience that when used on systems where very high water pressures are present, some of the non-adjustable-type regulators may allow a quick pressure surge to pass through just after the valve is opened. If you experience problems with drip tubing blowing out of the fittings right after the control valve is opened you may be experiencing this problem. Try switching to an adjustable-type pressure regulator.

Filters - to clean the water. Some companies tell you their products don't need a filter when used with city water but that’s at the expense of your future time and money! Save yourself dead plants and lots of grief and install a filter.

I suggest that you use a filter with a 150 mesh screen or one with a higher mesh number like 200 mesh. A good quality filter may be installed before the valve or pressure regulator, but the inexpensive filters often sold for drip systems should be installed after the pressure regulator. A good filter will have a maximum pressure rating of 10.3 bars (150 PSI) or higher.

If the package does not list the pressure rating it is probably an inexpensive, low-pressure model. I like to use a top quality filter and install it right at the water source so it protects the control valves and the pressure regulator too. Most valve failures result from sand or rust particles clogging the tiny passages inside the control valves! As long as you need to use a filter, why not get a good one and have it protect the valves too? It will probably pay for itself within 5 years by preventing a valve failure! Use a filter that is the same size as, or larger than, the valve.

Air Vent - to prevent air from being sucked into the emitters when the system is turned off. When the drip system is turned off the water in the pipes drains down to the lowest point, where it drains out of the emitters. As the water drains out it is replaced with air that is sucked into the tube through the higher emitters. As the air is sucked in, dirt may also be sucked in with it. The dirt may then get stuck and clog the emitter outlet. The purpose of the air vent is to allow air to be sucked in through the vent rather than the emitter. When used, the air vent is installed at the highest point on the drip tube.

  • Note: It is important to make sure that the air vent will not become covered with dirt or dirty water as that would allow dirt to be sucked into it. Always use air vents if the drip system is installed on a slope, as the elevation change creates a more powerful suction that will suck in more dirt. Air vents often are not used on smaller drip systems. If you don't use them just make sure the highest emitters aren't sitting where dirt can easily be sucked into them.

Flush Valve or End Cap - The end cap is important. Without it the water all runs out the end of the drip tube. (Well, duhhh...)

The water in a drip system flows very slowly in the tubes. This allows any sediment in the water to settle out, over time a layer of this sediment develops inside the tube and needs to be flushed out. Normally drip tubes are flushed once a year. If you have algae problems you may need to flush the tubes more often. Automatic flush valves are available that flush the tubing each time the water is turned on; I do not feel that most of these are particularly effective. Use a manual flush valve, or just use a simple hose-thread cap that you can remove to flush the tube.

  • Money saving tip: you can make a end cap/manual flush valve by just bending over the end of the drip tubing on itself to crimp off the flow. Use some wire or a cable/zip tie to hold the tube in the crimped position. Un-crimp and straighten the tube when you want to flush it.

Soaker hose, porous pipe, drip tape, laser tubing - various adaptations of the "extremely small-hole-in-a-pipe" type of drip system. They just have very small holes drilled (usually using a laser) into a tube, or are made from materials that create porous tubing walls that the water can slowly leak out of.

The advantage of these is obviously very low cost. The disadvantage is that the tiny holes are very easily clogged, especially with hard water containing lots of minerals, and for some products watering uniformity can be uneven. These types of systems are most often used in landscapes for portable irrigation (moving the tubes around the yard between irrigations tends to break the mineral deposits loose so they don't build up.

Garden Plot Layout

Enlargement of Drip Irrigation System

Resources

Much of this information is adapted from www.irrigationtutorials.com
Special thanks to Chase Fetter of Sage's Way Landscape and Design for his helpful information and tips!

 

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