Too much pressure can be a bad thing, but when it comes to lawn and garden sprayers, you must have adequate pressure. Without enough PSI you will have a weak and ineffective spray pattern.
I’ve been using lawn and garden sprayers for many years and out of curiosity I have done a fair amount of tests to see how different sprayers perform at various operating pressures. Typically, the optimal operating pressures for common garden sprayers are going to be in the 20-40 psi range. There are certainly several variables and other factors that could affect this number, but most sprayers will need this much psi to be effective.
In the rest of this guide, I am going to lay out what I have discovered and help you determine what pressure will work in your scenario. We will discuss what affects pressure and what pressure is needed for several different applications.
NOTE: Do not over-pressurize your sprayer. It will cause damage.
Understanding Spray Pressure
Spray pressure refers to the force at which a liquid—such as water, herbicide, or pesticide—is expelled from a sprayer. This pressure is typically measured in pounds per square inch (PSI). The right pressure ensures that the spray is dispersed in a pattern that provides adequate coverage and a droplet size that can thoroughly cover the target surface.
This article will focus on how pressure affects hand pump and backpack sprayers used for gardens, small orchards, lawns, etc. For more information check out this guide that covers how pressure affects other types of sprayers.
Typical Pressure Needed for Spraying Gardens
I think most people who use garden sprayers have an idea what adequate pressure looks like, however, putting a number on it can be difficult. In other words, what does 10 psi look like? How does it compare to what 40 psi looks like as it comes out of the nozzle?
The only way to know this for sure is to test it. So I rigged up a way to add a pressure gauge to the end of my spray wand. This way I could simultaneously see the spray pattern and the pressure. The exact pressure is not the important thing, it is knowing what pressure will get the best results, and then being able to get your sprayer to that level of pressure and maintain it.
I tested the pressure and spray pattern with two different types of nozzles: a flat fan and an adjustable cone/solid stream nozzle. What does pressure have to do with my spray nozzle you might ask? Well, the spray nozzle dictates how the fluid gets dispersed. It determines the shape of the spray pattern, the volume of liquid sprayed, and the droplet size produced.
In this video, you can see that the spray tip maintains a pretty consistent pattern down to about 10 psi. The droplet size and pattern become less consistent, and the flow slows as the pressure drops. Technically you would still be able to spray down below 10 psi. Although, it would be hard to ensure that you are applying the same amount of liquid over a given area.
The video also shows the solid stream nozzle that I tested. You can see that the nozzle produces a usable stream down below 10 psi. Of course, the volume of liquid and the distance decreases as the pressure drops.
So we could say that 10 psi is the minimum pressure needed from a garden sprayer but there are a lot of variables. The type of spraying as well as the type of spray nozzle that you use can make a world of difference.
Relationship Between Pressure and Nozzle Type
There are many different nozzle types. The most common types used in garden sprayers are solid stream, cone, and flat fan nozzles. We won’t get into all the different nozzle types in this article, but for more details, you should check out this guide on the different nozzle types and when to use them.
For the nozzle to produce a full, even, and consistent pattern, there needs to be adequate pressure from the sprayer. Pressure for a hand pump or backpack sprayer typically needs to be at least 10 psi to produce a usable and consistent spray pattern. Below this, the pattern may be inconsistent. For flat fan or cone nozzles, this could mean a narrower spray, for solid stream nozzles this means less distance.
Max Pressure of Garden Sprayers
Your sprayer will have a maximum pressure that it can be operated at and your nozzle will have a recommended operating range of pressure. Typically a garden sprayer will have a maximum PSI of around 40-45 psi. Some may be higher, especially backpack sprayers. Some of those models will reach 90 psi.
RELATED: Are Backpack Sprayers Worth It?
As mentioned before, manual sprayer pressure decreases once you begin spraying and the pump handle /lever must be worked continually to maintain pressure. With a hand pump or manual sprayer, it can be tough, because you can only “pump it” when you are not spraying. Your effective operating pressure ends up being between 10-40 PSI. Starting at about 40 and reducing from there.
At 20-40 psi you will see more consistency in the spray pattern or spray distance although the volume of liquid dispersed decreases as the pressure decreases (we will talk more about this in a moment).
RELATED: Beginners Guide to Spraying Your Lawn
Relationship Between Pressure and Droplet Size
Another aspect to consider is the droplet size that the sprayer nozzle is creating. Droplet size is essentially the diameter of the individual droplets dispersed. It affects both the coverage and the drift potential of the sprayed material.
The relationship between pressure and droplet size is inversely proportional: as the pressure increases, the droplet size decreases, and vice versa. Higher pressures cause the spray to atomize into finer particles, which can be advantageous or detrimental depending on the application:
- Higher Pressure: Produces smaller droplets, which can improve the coverage on leaf surfaces and penetration into denser foliage. However, smaller droplets are more susceptible to drift, which can reduce targeting accuracy and increase waste or environmental contamination.
- Lower Pressure: Results in larger droplets, which are less prone to drift and better suited for targeted applications. However, larger droplets might not provide as thorough coverage or penetrate plant canopies as effectively.
This is just the basics. You can learn more in this guide on sprayers and pressure.
Factors That Affect the Pressure of Your Garden Sprayer
Nozzle Size
Nozzle size plays a critical role in determining the pressure of a garden sprayer. Nozzle size refers to the diameter of the orifice through which the spray solution is expelled. In general, most lawn and garden sprayers will have a similar size nozzle. Typically, it is a red nozzle rated at 0.4 gpm at 40 psi.
Nozzle size is based on an international standard. In this guide I fully explain the different nozzle sizes and color code, but here are the basic principles:
- Smaller Nozzles and Higher Pressure: Smaller nozzles restrict the flow of liquid, which can increase the pressure within the system.
- Larger Nozzles and Lower Pressure: Larger nozzles allow more liquid to pass through with less restriction. This typically leads to a reduction in pressure, resulting in larger droplet sizes.
Nozzle size also can affect your spray distance. Generally, a larger, higher-volume nozzle would result in a greater spray distance. That is assuming your sprayer produces enough pressure to propel that fluid.
There are many factors at play here, so that is why I tested it. I explain this more in my post on how far a pump sprayer can spray.
Flow Rate
The flow rate and the type of pump play crucial roles in determining the operating pressure of a garden sprayer. Flow rate in a sprayer refers to how much liquid is expelled over a specific period, usually measured in gallons per minute (GPM). Flow rate is directly influenced by the sprayer’s pressure and the nozzle’s size and design.
Garden sprayers are typically equipped with manual pump assemblies limited to 40-60 psi max. The pressure combined with the nozzle size dictates the flow rate. The larger the nozzle the higher the flow rate, but the larger nozzle will mean a faster reduction in pressure as you spray.
So your spray distance or pattern will be affected sooner because the pressure in the tank escapes faster. This can be useful if you want to cover an area with a larger volume of liquid. It is not ideal if you want to keep a consistent spray pattern as you spray a row of plants or a larger area.
As I mentioned earlier, most garden sprayers come with a nozzle or assortment of nozzles. Typically a flan fan nozzle, a cone nozzle, a solid stream nozzle, or an adjustable cone/stream nozzle. The flat fan nozzles are typically red. Red nozzles are rated at 0.4 gallons per minute at 40 psi. At 20 psi they only flow 0.28 GPM.
This is key to remember, because if you are using the nozzle to broadcast spray, whether with a boom or by hand, your output changes as pressure drops. So if you walk or drive at a constant speed but your pressure fluctuates, you are applying the product inconsistently.
Achieving Consistent Pressure
Consistent pressure is key to producing uniform droplet sizes throughout the spraying process. As mentioned previously, the size of the droplets can significantly influence the effectiveness of the chemical being applied.
The droplet size can vary when pressure fluctuates, leading to uneven application. This inconsistency can result in areas where the pesticide or fertilizer is applied too heavily or too lightly, affecting the health and growth of the plants.
Consistent pressure can be tough to achieve with manual hand pump sprayers like hand tank sprayers and backpack sprayers. When using one of these sprayers, as soon as you pull the trigger the pressure will decrease. With a hand pump sprayer, you pump the handle, then pick up the sprayer and sprayer.
While you may start at 40 psi your pressure will gradually decrease. As this happens you will notice that your spray pattern and droplet sizes change. You can avoid this pressure fluctuation somewhat with a backpack sprayer because you can continue to pump the handle as you spray. The other option is to use an electric or battery-powered sprayer.
RELATED: Calibrating Your Sprayer
Typical Operating Pressure Different Types of Garden Sprayers Can Produce
I tested the operating pressure range of a hand pump sprayer, two types of backpack sprayer, and a 12-volt spot sprayer. Here are the maximum pressures that I was able to achieve as well as the effective operating pressure range:
| Pump Type | Max Pressure (PSI) | Operating Range (PSI) |
| Hand Pump Sprayers | 40-45 | 10-40 |
| Backpack Sprayers | 60*, 90^ | 10-60*, 10-90^ |
| 12-Volt Sprayers | 40-60 | 20-40 |
Pressures Needed for Different Types of Spraying
I also tested each sprayer in different scenarios. Here are the pressure ranges needed for the sprayer to be effective in each task:
| Spraying Task | Pressure Range (PSI) | Nozzle Type |
| Spot Spray by Hand | 10-40 | Cone Nozzle |
| Broadcast Spraying with hand pump sprayer | 20-40 | Cone or Flat Fan |
| Spray Small Trees (20-25ft tall) | 40-90 | Solid Stream |
| Broadcast spray with boom | 20-60 | Tapered Flat Fan |
Conclusion
Achieving the right pressure is critical for effectively using lawn and garden sprayers. While too much pressure can lead to damage and inefficiencies, insufficient pressure results in weak and ineffective spray patterns that can compromise your gardening efforts.
For more insights into how pressure affects spray patterns, droplet size, and overall sprayer performance, consider exploring related posts on Sprayer Guru:
