Have you tried to use our Drip Wizard only to be confronted with a message saying that the total length of tubing is greater than 360 feet?

What does that mean?

Each drip irrigation circuit is limited by the following:

• The water supply in gallons per hour
• Changes in elevation
• Friction losses in the 1/2" Tubing mainline and/or in 1/2" Dripline

The first is usually not a problem. Most residences have more water supply than necessary for each drip irrigation circuit as long as the circuits are turned on at different times of day and do not compete with one another.

Let's disregard changes in elevation for now and assume that most residences have no more than a 10 foot change in elevation. More about that in another article.

The third factor, friction loss in the tubing, is what limits most residential drip irrigation circuits.

A general rule is that a single length of 1/2" Tubing and Dripline in a circuit should be no more than 200 feet ... (see exceptions)

...and that the total flow should be no more than 180 gallons per hour which is 180 drippers at one gallon per hour or 90 drippers at two gallons per hour or 9 sprayers at 20 gallons per hour... (see exception)

If a drip irrigation circuit exceeds those limits, one-gallon per hour drippers close to the start of the circuit may be delivering one gallon but drippers at the far end may only be delivering 1/2 gallon per hour due to the friction loss of water running through a single length of tubing.

The result is that plants are receiving an uneven distribution of water.

Exceptions to the Length Rule

What if you have a single length of 1/2" tubing 310 feet long? Will it work?

Actually yes, as long as the total rate of flow from all drippers is less than 75 GPH. You can even have an overall length of 460 feet if the rate of flow is less than 50 GPH. That's not many gallons per hour. Most residential drip irrigation circuits end up using more like 150 gallons per hour per circuit which is why the general rule about a maximum length of 200 feet for a single length of tubing.

But will 310 feet work? It also depends on the plants you are serving. If the plants at the far end of the circuit are not too fussy about the amount of water, such as shrubbery, an overlength circuit may work fine.

If the tubing runs downhill, friction losses in the tubing can be offset by the effect of gravity as the water runs downhill.

But if you are watering a valuable row crop such as strawberries or cabbage, it's important that all plants in the row receive the same amount of water so that they all mature at the same time.

In the end, experience is the best expert. Take a look at the drippers on a long circuit. Does the first dripper and the last dripper deliver the same amount of water?

The beauty of a drip irrigation system is that you can experiment with an overlength circuit and do no harm. If you're not satisfied, it's easy to change the system to two circuits with no loss of parts. Every part can be used and reused.

Solutions

First, reduce any unnecessary lengths of 1/2" Tubing.

If there is a long length of 1/2" tubing that crosses a lawn to the garden, flower bed or greenhouse, consider replacing it with a large-diameter garden hose or 3/4" or 1" rigid PVC pipe or poly tubing under house water pressure. Then set up a standpipe where your drip irrigation circuit starts. See the How-To article on standpipes.

Second, keep the pressure high

Make sure that you are using a 25 PSI or 30 PSI pressure regulator which is the maximum for a drip system.

Third, isolate part of the circuit

If part of the circuit only needs water part of the time, consider using an inline valve to isolate that part of the circuit. Open the valve by hand whenever you wish to include that zone in the regular watering shedule.

Fourth, add another circuit.

You can set up a second circuit on a separate faucet or add a second circuit on the same faucet.

Avoid having two timers hanging on the same faucet. The weight can damage the faucet or the pipe in the wall that supplies it.

Instead, hang one timer on a manifold at the faucet and also attach a short length of garden hose to the manifold. Attach the other end of the garden hose to a nearby standpipe and attach the second timer to the standpipe.

Timing

If you set up a second timer and circuit on the same faucet, program the timers so that they start at different times of day. That way each circuit has full water pressure and doesn't compete with another circuit.

You could actually keep adding more circuits and more timers as long as only one circuit is programmed to turn on at a time.

An inline valve can be used to isolate part of a circuit - details

Above - a manifold is great for attaching multiple hoses and a timer to an outdoor faucet.

Below is a standpipe in a greenhouse. A garden hose is used to bring water under house pressure to the standpipe, which cuts down on the length of 1/2" Tubing we need for the circuit.