If you've ever used drip irrigation, you can probably remember a time where you looked at the group of components connected to your spigot and thought "I hope that works right, because I don't understand what any of those things do". We get it, drip irrigation is intimidating! That's why we're bringing you this installment in the Drip Irrigation – Demystified! blog series covering the head assembly. This post will be the first of five, each covering a different component. By the time you're done with the series, you'll understand what the head assembly is, what each component does, why it works, and why it's important for the proper functioning of your system.
Before we get into discussing today's topic, let's introduce the head assembly in general.
The head assembly is a collection of parts that ensure the water entering your system is clean, at the right pressure, and flowing in the right direction to be properly utilized. It consists of a timer, backflow preventer, filter, pressure regulator, and tubing adapter.
It's important to remember that the head assembly is a collection of parts, not a single item! Even if your head assembly is all put together when you get it, it's still made up of individual parts. Don't make the mistake of thinking you need to replace the whole thing just because one part isn't working right.
Hint: if you ever see something referred to as an "assembly", that usually means it's made up of parts that can be disconnected or replaced if needed.
Think of the head assembly as the security checkpoint for your irrigation system. You want to have all these parts right at the front of your system for the same reason airport security checks happen before you get on the plane. The tasks that the components of the head assembly perform are so critical that they need to be done before the water gets to any of the other parts of your system, such as the drippers and sprayers that actually water your plants. This is why it's called a head assembly: it's an assembly of parts right at the head of your system.
Knowing what the head assembly does on a conceptual level is great and all, but what really matters is knowing exactly what each of the components do and why it matters for your drip system. We'll follow the flow of water through your head assembly as we explore the function and use of each component. That means we need to start with the brains of the whole operation: the timer.
The Timer
An irrigation timer (also called a "controller") is an automatic, programmable valve.
- Automatic means that the timer doesn't need you there to start or stop its functioning
- Programmable means that you can tell the timer what you want it to do, and it will remember those instructions and keep doing them automatically until you tell it otherwise
- Valve means that it has the ability to start and stop the flow of water by opening and closing
All of these functions allow your timer to do the work of turning the system on and off for you, which can be a huge hassle. The most common type of timer is what's called a hose end timer, aka a timer that connects to a garden hose or spigot. While there are other types, we're going to focus on hose end timers since it's the most popular type for home gardeners.
Hint: all garden hoses and hose spigots/spickets/taps in the US are ¾" hose thread. If you see a hose or spigot, you can be certain that the threads are ¾" hose thread!
The timer goes right onto your hose or spigot, making it the first part of the head assembly and the very first part of your system that water touches. There are two good reasons for this. First, the timer is a valve, which means it can start or stop the flow of water. Having this at the front of your system means you can use it to turn the whole system on or off. The second has to do with constant pressure, which we'll address a little later.
Note: there are use cases for having valves (both automatic and manual) in places other than the front of your system, but that's a topic for another blog.
Timer Features
There are a large variety of irrigation timers out there, many of which have unique features. Too many features for me to cover in a single article, in fact. Instead of getting into the nitty-gritty of every potential feature, I'm going to describe some basic ones that (almost) every timer has. If you get a hose end timer, you can be fairly certain that it will have these capabilities:
- Multiple start times. A "start time" is exactly what it sounds like: a time that the valve inside the timer opens. Some simpler timers (like analog two-dial models) may require you to have these start times at consistent intervals from each other, such as every six hours, twelve hours, etc. Digital timers will usually let you choose up to four unique start times per day
- Runtime options. Runtime refers to how long the valve stays open for after a start time. Most timers will give you pretty fine control over the runtime – down to the minute in a lot of cases – with a minimum runtime of five minutes and a maximum of almost six hours. After the runtime ends, the valve in the timer will close, turning the system off
- Manual on/off. This is a button that lets you manually open or close the valve inside the timer. That's useful if it starts raining while your system is running, or if you decide you want a little extra water on a particularly hot day and don't feel like messing with the program. Since this is a button, it generally requires power for it to work. If the timer is dead, the button won't do anything
- Watering days. Digital timers will let you choose which days of the week to water. This is handy if you don't want to water every single day or on a cyclical schedule like every two or three days. Each day will typically have four start times, and you can choose as many or as few as you like. Keep in mind that while the days themselves aren't cyclical, the week or month may be. Hose end timers don't typically have a full 365-day calendar to program. They'll give you a week or month to program, which will repeat until you change the program
- Batteries. While there are some solar-powered hose end timers, the vast majority run on batteries, either 9v or AA. The power draw is very low, so the batteries usually last at least a year
- Weather resistance. Most hose end timers are weather resistant and don't need to be indoors or protected from the elements. The big exception here is freezing. If you leave your timer out in the winter, it's likely to break. This is especially true if you let it freeze with water inside it. It's a good idea to bring your timer inside during the winter.
Hint: Timers that have been properly winterized in an in-ground valve box and AC timers that don't come attached to a valve aren't as prone to winter damage. It's not the timer part itself that breaks in the winter, but rather the valve. Water expanding as it freezes is the cause of most winter damage to irrigation equipment
Constant Pressure
Earlier I alluded to a second reason why the timer needs to be the first part of the system that the water touches. That is due to constant pressure and its effects.
This concept is critical to a complete understanding of the head assembly, as misunderstanding it is liable to cause severe issues and the potential for significant leaking.
The timer needs to be the first part of the system because it is made to withstand constant water pressure. Most plastic irrigation components – like the other parts of the head assembly – are not designed to be under constant pressure. Having the timer upstream of those components protects them from the effects of constant pressure, vastly extending their lifespan.
Constant pressure is required for an automatic irrigation timer to operate properly. If you go back to the definition of the timer, you'll see that the automatic valve doesn't pump water or create flow, it simply opens and closes. The purpose of a timer is to turn the system on and off automatically, which means that opening the valve inside the timer needs to "start" the system. This can't happen unless there is pressurized water on the other side of the valve. Think about it like the doors to a concert hall. If there are people waiting to enter, then opening the doors lets people in. If there's nobody on the other side of the doors, opening them doesn't magically create people to walk inside.
Since having constant pressure is essential to an automatic timer being automatic, it is constructed out of materials that can stand up to that pressure. The other components of the head assembly are made of less resilient materials to save on costs. This doesn't mean they're not sturdy, just that the types of plastic and seals they use are designed to withstand weather, sunlight, and impacts instead of the forces of constant water pressure.
Note: these components all experience water pressure when the system is on, and that's fine. Once the system turns off, only the timer still experiences the pressure. That's why we call it "constant" pressure. Over time, that constant pressure would wear out the other parts.
The real-world impact of this is that you will typically need a separate head assembly for each automated zone of your drip system. Since the timer has to come first, you can't use one backflow preventer, filter, and pressure regulator upstream of a multi-outlet timer to save money. If you do that, those components will break down under the constant pressure, causing massive leaks.
Now you may be thinking "well, I'll just go close the spigot when the system isn't running to make sure there isn't constant pressure," but that doesn't solve the problem. Remember, without constant pressure, the timer doesn't work. You'd need to go out to your spigot and turn it on whenever you want to run the system, defeating the purpose of having a timer.
Programming
Like features, timer programming varies a lot model to model. Every timer should come with an instruction manual that explains how to program it. We have links to Youtube videos going over how to program our most popular timers, which is very handy for those who like to learn visually. The best resource if you're having trouble programming a timer is to contact the manufacturer directly.
Conclusion
A timer isn't only a convenience in the garden, it's the cornerstone of any automated irrigation system. It saves water by allowing for tailored watering schedules and helps protect downstream components from the effects of constant pressure. While it can look intimidating, the timer is no more complicated than any other valve.
The next installment of Drip Irrigation – Demystified! will continue down the head assembly to the backflow preventer, your system's safeguard against irrigation water contaminating the plumbing in your house.
FAQ
Q: What is a drip irrigation head assembly?
A: The head assembly is a collection of parts that ensure the water entering your system is clean, at the right pressure, and flowing in the right direction to be properly utilized. It consists of a timer, backflow preventer, filter, pressure regulator, and tubing adapter.
Q: Is a head assembly one part?
A: No, a head assembly is made of multiple different components that can be swapped or replaced as needed.
Q: What part of the head assembly comes first?
A: If your head assembly includes a timer, then you should always put the timer first. If not, put the backflow preventer first
Q: Is an irrigation timer the same as a controller?
A: Yes, they're often used interchangeably
Q: What is an irrigation timer?
A: An irrigation timer is an automatic, programmable valve often used to turn irrigation systems on and off automatically
Q: What is a hose end timer?
A: A hose end timer is a timer that connects natively to a spigot/hydrant/spicket, or to the end of a garden hose
Q: How many start times do timers typically have?
A: Most hose end timers have four start times per day
Q: How long can you set an irrigation timer to run for?
A: Hose end timers typically allow runtimes from 5 minutes up to 5 hours and 59 minutes
Q: Can you put your filter, pressure regulator, or backflow preventer before your timer?
A: No, you shouldn't put those components before your timer. Most plastic drip irrigation equipment isn't rated for constant pressure, so putting them upstream of the timer will cause them to leak.
Q: Does my timer need constant pressure to work?
A: Yes, your automatic timer won't work unless there is constant pressure upstream of it. Think about it like the doors to a concert hall. If there are people waiting to enter, then opening the doors lets people in. If there's nobody on the other side of the doors, opening them doesn't magically create people to walk inside.
Q: Do I need a separate head assembly for each outlet of my timer?
A: Yes, you should have a head assembly for each outlet of your timer. Skipping the head assembly can have wide-ranging effects on your system such as clogged drippers and leaking fittings.
