Drip watering systems can be operated by gravity.
Gravity as an energy source is free. As a home gardener, you can tap this natural power. Any drip system requires pressure to operate, so your challenge is to use gravity to create some pressure, and then work with the pressure you have to help your garden grow. Does this Spark an idea?
Elevate
To create 1 lb. of pressure per square inch, a gravity drip system requires 2.3 feet of height, also called "head." To achieve 10 PSI, your water source, usually a tank, needs to be located 23 feet above your garden plot. To produce five PSI, the tank would need to be 12 feet higher than the ground you intend to water. One way to get the water source high enough is to position a tank on top of a building or on a hill above the garden plot. Another way is to build a stand to elevate the tank.
Ten PSI requires no pressure regulation and is likely to provide enough pressure to keep water flowing. It is possible to have a working gravity drip system with less than 10 PSI, but there are a few methods you will probably need to employ.
Filter
A drip system depends on there being some turbulence in the water to keep fine debris and silt in suspension. Higher pressures create higher turbulence, while lower pressures minimize turbulence. Without turbulence, fine dirt and organic particles settle and clog the drippers. Water, especially at the end of a drip circuit, may cease flowing.
Drippers rely on high turbulence in the water to keep silt and fine organic material suspended in the water long enough to flush out. Low pressure results in low turbulence. Silt in the water may settle and clog the small openings in drippers in time. One way to combat this problem is to filter the water before it enters the drip line.
Compensate
When designing a gravity drip system, you will need drippers and drip lines that work with low pressure. The drippers control the flow of water as it drips onto the plants. A D1 dripper drips one gallon of water per hour, while a D2 drips two gallons and a D3 drips three gallons. Drippers attach to drip lines into which water from your source flows. Commonly used gravity drip lines are 1/2-inch diameter lines such as DL4100 or 5/8-inch line such as DL6200. These may be available from home improvement stores or garden supply stores. Keep the length of your drip circuits short. Long lines of tubing are likely to lose pressure and cease functioning, while short lines are more likely to remain open.
Test
Do trial and error testing. Start with a small basic system and see how it operates. Add to it and test to see if the gravity drip diminishes. If you lose water flow, you will have isolated the problem and will be able to address it by increasing the diameter of the tubes, improving your filtration or repositioning your water source.
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