Drip irrigation tubing is one of most important components of a drip irrigation system. It is responsible for delivering water to the sprinklers, emitters and misters. Without it, the water flow to plants is cut off.
There are several types of drip irrigation tubing, each with its own specific purpose. The most common types are: 1/2 inch distribution tubing, 1/4 inch distribution tubing, soaker tubing and emitter tubing. Installing the proper drip irrigation tubing for your drip irrigation system is extremely important.
1/2 inch distribution tubing is used as the main water supply. It runs from the tap to the 1/4 inch distribution tubing, soaker tubing and emitter tubing. It can be used either above or below the soil. If you are to purchase this type of drip irrigation tubing, you can choose either one of these length: 50, 100 and 500 feet.
1/4 inch distribution tubing is used to connect the 1/2 inch tubing to the sprinklers, emitters and misters. It is the supply line so you need to punch a hole in it and connect it to a 1/4 inch barbed coupler.
Soaker tubing is similar to soaker hose. You need to connect this drip irrigation tubing to the 1/2 inch supply line using the 1/4 inch barbed connector. But if you want to connect it to the 1/4 inch supply line, use the 1/4 inch barbed tee connector.
Emitter tubing is the drip irrigation tubing used for spot watering, designed specifically to put an emitter every 12 inches. Just like the soaker tubing, you need to connect it to the supply line with the 1/4 inch barbed connector.
an alternative article here : http://www.ehow.co.uk/list_5974541_types-irrigation-pipe.html