We are often asked if gravity feed will work with a drip irrigation system. The answer is yes, but there are limitations. Gravity feed systems often operate at very low pressures but all drip irrigation systems require minimum pressure.

How much pressure is needed? Most drippers and dripline require 10 PSI, and 15 to 30 PSI is best. Pressure compensating drippers such as the D4, D5 or D45 need a minimum of 10 PSI to open due to a valve inside the dripper that prevents drainback at shutdown.

Very low pressure

Can you operate a drip system with less than 10 PSI? Yes, but be sure to use non-pressure compensating drippers such as the D1, D2 or D3 or non-pressure compensating dripline such as the DL4100 or DL6200.

The lower the pressure, the greater the effect of friction losses in the tubing that will slow the flow of water. If the pressure is too low, the drippers at the end of the circuit may not flow at all.

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 over time.

Choose non-pressure compensating drippers such as the D2 for low pressure drip systems

Non-pressure compensating dripline such as the DL4100 will also work in low-pressure gravity feed drip systems

DL6200 Thinwall Dripline is suitable for low-pressure drip systems

This is the adapter you need to tap into the bottom of a water barrel. It's a FA27

T8300 flat tubing is 2" in diameter and ideal as a low-friction supply line to the field. It will carry 30 gallons per minute at a friction loss of about one PSI per 100 feet of tubing

Design criteria

It is possible to operate a drip irrigation system with less than 10 PSI. Here are some design criteria to consider:

• Use non-pressure compensating drippers or dripline.
• Keep row length as short as possible.
• Position the water source on the high side of the field and let gravity help the flow.
• Elevate the water source as much as possible to increase pressure.
• Oversize any long lengths of tubing to reduce friction losses in the tubing.
• Experiment by setting up part of the system and test before adding more rows.

Very low pressure drip irrigation is possible but be prepared to experiment to see what will work in your garden or crop area.

How much elevation?

It takes 2.3 foot of height (head) to produce one pound per square inch (PSI) of water pressure. In other words, your water tank must be 23 feet above the field to produce 10 PSI or 12 feet up to produce 5 PSI. You can place the water tank on a hill or high in a barn or other building. You can build a tall stand. The higher the better until you reach 70'. Above that height, a gravity feed system will produce more than 30 PSI and will require a pressure regulator to keep the pressure at 30 PSI or less.

If your gravity feed water tank does not have an outlet built in, use a FA27 Adaptor as a bukhead fitting to tap into the side or bottom surface of a plastic or metal water tank. It will fit as long as the surface is smooth and flat or very close to flat. It has a thick flexible washer that helps seal watertight.

Alternatives

If you don't have access to electricity and a gravity feed system is not possible, you can use a gasoline or diesel-fueled portable pump. It is also possible to add a water pump to a tractor or truck.