Using a drip irrigation system can make gardening easier and more rewarding, but it can be quite technically involved if you want to do it right. Pressure is one of the most commonly misunderstood characteristics of a drip irrigation system. If it’s too high or too low, your system won’t work right, so it’s important that you understand what pressure is and what it does for your system.
What Is Water Pressure?
To put it simply, pressure is the force with which water moves through your system. Ask a physicist or a hydraulic engineer, and they’ll give you different answers, but when it comes to your backyard drip system, this definition works just fine. Pressure is force. It pushes the water through the pipes and pushes against the walls of your tubing.
On a similar note, remember these two things: water still flows even with functionally zero pressure, and water always wants to find the path of least resistance.
What Isn’t Water Pressure?
Water pressure IS NOT how much water comes out of your system. This is the #1 thing that confuses people when designing or troubleshooting a drip system, so I’ll repeat it: Water pressure IS NOT how much water comes out of your system! That’s flow rate.
Why Does That Matter?
Pressure and flow rate are related, but they’re not the same thing. You can have a system with high pressure that only moves a very small amount of water, and you can have a system that moves a lot of water at a relatively low pressure. Remember, water will still flow along the path of least resistance even with functionally zero pressure!
Imagine two straws: one teeny-tiny skinny one from a coffee shop, and one big fat one from a milkshake place. You want to use these straws to squirt water at your brother (and co-worker) because he’s annoying you, so you fill your mouth with water. When you use the small straw, you might be able to shoot the water farther, but only a small amount of water comes out, no matter how hard you push with your mouth. AKA, no matter how high the pressure, you can’t go over a certain flow rate. The milkshake straw is the opposite: you barely need to try to shoot all the water out of it. AKA, you can have a lot of flow rate without a very high pressure.
Understanding the difference between pressure and flow rate will make troubleshooting a malfunctioning system much easier, and it will help you design new systems more effectively. We’ll cover that more in a moment.
How Pressure Interacts With Your Drip System
The primary way that pressure influences the operation of your drip system is through the emitters. Every emitter has a minimum pressure requirement, which is the minimum pressure that will allow it to operate properly. This varies emitter to emitter, but most of them fall somewhere in the range of 15 PSI to 30 PSI. If the pressure is below the minimum, then the emitter will work poorly, or may not work at all. This is because emitters aren’t just holes in plastic. They use a maze-like pattern inside them to slow the water down, which is what allows them to have specific flow rates like 1 gph, 2 gph, etc.
What happens if the pressure is too high depends on the type of dripper and just how high the pressure is. For normal, non-pressure-compensating drippers, higher pressure will increase the flow rate of the dripper (to a point). For pressure-compensating drippers, higher pressure will actually decrease the flow rate. This is due to pressure-compensating drippers having a flexible diaphragm that acts as a “roof” over the maze inside them. The high pressure pushes that diaphragm down onto the maze, which restricts the flow. Eventually, too-high pressure will cause the drippers to pop off the line, though that’s pretty hard to do with home water pressure.
Pressure affects basically every part of your system - water velocity in the pipes, how much pressure your system loses over distance, how your solenoid valves work, etc - but the interaction with emitters is the most consequential for day-to-day troubleshooting.
How Pressure Issues Manifest
The primary way that you’ll notice pressure issues in your system is due to malfunctioning emitters.
Low pressure can show up in a few different ways. If the pressure is too low at the input (such as your spigot), then you may see all of your emitters working at partial capacity or not working at all. Remember, emitters need a specific minimum pressure to operate, so if your system doesn’t have enough pressure, they won’t work right. That being said, you should also remember that pressure goes down over distance due to friction with the walls of the pipes. This means that even if your input pressure is high enough for the first few drippers, by the time the water reaches the end of your system, it may drop below the minimum pressure for your emitters. Whether that happens depends on factors such as pipe size and material, flow rate, elevation change, and total distance. When this happens, you’ll usually see the emitters closest to the source working properly while the emitters further away perform worse and worse.
There’s an annoying wrinkle here when it comes to troubleshooting low-pressure issues. Namely, that low flow rate issues often manifest in the same way. If your system doesn’t have enough water available to it, you will often see emitters putting out less water than they’re supposed to, or no water at all, and you’ll often see those problems get worse as the emitters get further from the water source. Not only that, but systems with a low flow rate will have a weak flow of water, which often leads people to mistake the issue as being “low pressure.”
High pressure is a little more obvious. Leaks from connection points, spraying or squirting non-PC emitters, and water hammer - the slamming sound you sometimes hear when turning water on or off - are all signs of the pressure being too high. If you have pressure-compensating emitters, then be on the lookout for the flow of the emitters being too low, as that can be caused by the pressure being too high. That said, most pressure-compensating emitters won’t experience this issue until the pressure is over 50 psi.
How to Troubleshoot Pressure Issues
Before we get into specific troubleshooting steps, there is one important thing to know about fixing pressure issues: it’s easy to fix high pressure and hard to fix flow pressure. If your pressure is too high, you can usually add a pressure regulator to your system to bring it down to a more appropriate level. These regulators can cost as little as $5 and are typically easy to install. If your pressure is too low, it’s a much more difficult fix. Removing a pressure regulator might help, but oftentimes it requires significant changes to your zoning, installing a booster pump, or contacting your local municipality to increase the pressure coming off your water main.
Anyway, once you identify an issue, you’ll want to use the info in the section above to determine if you think the problem is high pressure or low pressure. If you think the pressure is too high, buy a pressure regulator or replace your existing one. Most drip systems want to work at about 25 PSI, but feel free to call us if you have any questions about the right regulator for your system.
If you think your pressure is too low, then there are a few things you can do. The simplest one is to buy a pressure gauge and test your pressure. This can save you a ton of time troubleshooting your system. Take a look at the “description” tab of our pressure and flow testing tool for a step-by-step guide on how to properly test your system pressure.
Since low pressure can be hard to fix, it’s best to ensure that there’s nothing else causing your issues. You don’t want to go through the hassle and expense of buying and installing a booster pump just to have your problems persist.
- Ensure all your valves are open all the way. This includes your spigot and any manual ball valves on your system. This is the plumbing equivalent of the classic “Is your computer plugged in?” troubleshooting step. If any of the valves on your system are not fully open, open them up. It’s a common misconception that closing a ball valve partway will decrease pressure, and we often see people complaining of “low pressure” when it’s really a partially closed ball valve restricting the flow. Open them all the way!
- Unhook your system from the spigot and turn it on all the way to make sure water is actually coming out of it. Don’t just rely on hearing the water coming out of it; actually look at it! I once spent four hours troubleshooting a system where the issue ended up being that the spigot was faulty and was barely putting out any water. Doing this step will help you avoid having to spend four hours on the phone with me!
- If you have a pressure regulator on your system, take it off and try running the system without it. The worst that will happen is that you might pop a fitting or emitter off, so it won’t hurt to try it. If that doesn’t happen and your system works properly instead, then congratulations! You fixed it!
- Inspect all of the emitters on your system. Sometimes, clogs or buildup in an area can make you think you have a systemic pressure issue when the reality is just that you have a few clogged emitters. If it’s just a couple of emitters acting up, try replacing them to see if it fixes your issue.
- Open the ends of your system and turn the water on at all blasts. This will help to flush out any debris that might be restricting the flow in your system. Remember that you’re supposed to do this during installation before pressurizing the system.
- Conduct a flow rate analysis of your system. To do that, add up the flow rates of all the emitters on your system, then compare it to the capacity of your tube (220 GPH for ½” and 480 GPH for ¾”). If your flow rate is over the capacity, then that is likely causing your problems. If you need help doing this analysis or figuring out how to fix this issue, give us a call!
- Test the flow rate of your water source against the total flow rate of your system. If you’re trying to use more water than your water source can provide, then your system won’t work right. This is exactly the reason why the Colorado River is a raging torrent in Colorado and a muddy trickle when it gets to the Gulf of Mexico! Check out the description tab on this page for more info.
- Consider the length and grade of your system. ½” tubing has a max recommended run length of about 400’, and ¾” is recommended for about 600’. If your system runs further than this in any one continuous run, then you should consider replacing some areas with a larger diameter PVC mainline. This will help reduce pressure loss over distance. Likewise, if your system is on a steep hill, you might be losing a bunch of pressure to gravity as the water travels up the hill.
- Check your filters. A filter element full of gunk will restrict flow and reduce pressure.
As you’ll have noticed, a lot of these steps have to do with ensuring you don’t have a flow rate problem. This is a good idea for two reasons. First, all of these are things you can do without buying anything! A free fix is a good fix, after all.. Second, it’s relatively easy to fix issues with flow rate by reducing the flow of your drippers, increasing your tubing size, or adding zones or water sources. Only if you have determined 100% that your problem is due to low pressure and that you can’t fix it by adjusting the flow rate should you look into increasing your input pressure, as that can be expensive and time-consuming.
Still Have Issues or Questions?
Drip irrigation is complicated, and we get that! Everyone runs into problems they can’t figure out now and then, from the noobiest noob to the most masterful of gardeners. If you’re having issues with your drip system, give us a call at 877-597-1669, email [email protected], or schedule a free phone consultation. Sometimes, even a problem that looks unfixable can be solved with a call to one of our experts.
