In gravity feed irrigation systems water takes the path of least resistance. If you place drip tubing or garden hose on the ground and punch holes every few inches, the openings closest to the water source will discharge much more water than the openings farther down the line. If the distance is long enough, water may not reach the last holes on the line. Distance could be as long as 50 feet or as little as 10 feet. This will depend on the height of the bucket/barrel, the pressure available, the size of the pipe and the flow uniformity of the system.
By selecting a low flow dripper, such as .5 GPH (2 L/H), and then raising the pressure by raising the height of the bucket from the ground, the efficiency and uniformity of a gravity feed drip irrigation system can be improved the use of drippers gives better control of flow rate than poking holes in the tubing, and the water passage structure of the dripper gives a better uniformity to the irrigation system.
With gravity feed drip irrigation system you may need to fill the barrel daily, or every other day. The only ways to adjust the time to empty the barrel, or to adjust the drippers' flow rate, are to close the ball valve in front of the barrel, change the height of the barrel, the volume of the barrel, and/or the total number of drippers in the system. Note that with gravity feed systems the size of the system is limited by the size of the barrel; in general, a barrel large enough to provide adequate flow and pressure to increasingly larger areas would quickly become unmanageable. As more outlets (drippers) are added to the line, uniformity decreases, with more water at the beginning of the line and less at the end. In addition, as the water level in the barrel drops, the drippers' flow rate drops.
To have an effective gravity feed drip irrigation system; consider the size of the barrel and the number of drippers. Our suggestion is to make sure that the flow rate per outlet is at least .03 GPH
Like drip irrigation system, gravity feed systems using drip irrigation need a minimum pressure to operate. To gain pressure in gravity feed systems, use this calculation:
To gain water pressure by using gravity means you must raise the water source (barrel) above the system lines. For every 1' (12 cm) of elevation above the system there is a gain of .433 PSI (.030 bar). This means that if the water source is 10 feet (3m) above the system there is a pressure of 4.33 PSI (.30 bar) at the start of the system (.433 x 10 = 4.33).
Keep in mind that low pressure, such as 4.33 PSI (.30 bar) or less, will lead to:
10 x 12 foot gravity feed system with 5 rows, each 10' long using a 1/4"drip line with pre inserted drippers every 12" (30 cm):
The chart below is for a gravity feed drip irrrigation system using a 1/4" drip line with drippers every 12" (30 cm). This design uses a 10 gallon (38L) bucket with 9 gallons (30L) of water at a pressure range less then 1 PSI on flat terrain
|Barrel Size||Height above the drip system||Length of drip line run||Dripper Flow rate||Container close to empty in:|
|50 gallon||8"||10'||.034 GPH 1.28 l/h||Around 2.50 hours|
|50 gallon||12"||10'||.036 GPH 1.36 l/h||Around 2.40 hours|
|50 gallon||12"||14'||.041 GPH 1.55 l/h||Around 2.30 hours|
|50 gallon||16"||14'||.042 GPH 1.58 l/h||Around 2.20 hours|