Answer: There are so many variables involved and possible components, that entire books are written on the subject! A drip irrigation install is beyond the scope of this Q&A, but I'll give you some info to get started.
Backflow Prevention Assemblies. These units are required by city code for all types of irrigation systems. Their function is to stop contaminated water from being sucked back into your drinking water system.
A good controller should have three major functions. It should let you set multiple programs, which will accommodate the needs of different types of plants. It should have the capability run program times of two hours or more, so enough water soaks through a plant?s root system. The controller should allow intervals of 14 days or more between irrigations. This is because plants don?t need as frequent watering in winter and as they mature irrigation schedules can be extended. Other useful features include a ?rain? or ?off? setting so you can skip an irrigation without losing the programmed schedule, and a battery back-up to save programs if the power goes out.
Valves turn the water supply on and off. When wired to a controller, the valve will open and close on the days and times you have programmed. Many irrigation systems are installed with just one or two valves, which is almost always insufficient for an entire landscape. Different types of plants have different water requirements. For example, native and desert-adapted plants need less frequent watering than exotic species. Trees need deeper watering to wet their entire root zone than vegetables gardens. Lawns should always have their own valve. There should be a separate valve for plants with competing needs, both to grow healthy plants and to use water wisely. So think about irrigation from your entire landscape's needs, not just your vegetable garden. It will be cheaper in the long run than retrofitting with separate parts and sections.
This is usually a flexible polytubing or PVC attached to the valves, carrying larger amounts of water underground to a place in the yard. Attached to that is microtubing, sometimes called spaghetti tube, with drip emitters at the ends that deliver smaller amounts of water to the plants. Or, some type of soaker hose might be used instead of tubing and emitters.
Plants that will remain small (1-3 feet in diameter) such as groundcovers and perennials usually require only one emitter, but larger plants should have emitters spaced evenly around a plant?s perimeter to encourage balanced root growth. With vegetable gardens, depending on size and layout, soaker hose, laser hose, drip tubing or similar is often used because it wets a larger area for closely placed plants.
I hope this gives you a place to start. Good luck!
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