Whether you are building your own sprayer or just looking for a replacement pump, identifying the correct size pump is essential. There are many types of pumps, flow rates, pressures, and more. If you are looking for help sizing a pump for your situation, look no further, I plan to cover everything you will need to know when it comes to sprayer pump size.
What Size Pump Do I Need For a Sprayer?
When someone refers to “pump size” they usually mean the flow rate of the pump. However, the amount of pressure a pump can produce is just as important for some sprayer types, and a higher flow rate doesn’t necessarily mean more pressure.
The type of sprayer that you have or want to build will determine the type of pump you need and from there you can determine the pump flow and pressure you will need.
Here are some common sprayer types and the type of pumps used on those sprayers:
| Sprayer Type | Example | Pump Types |
|---|---|---|
| Lawn & Garden Sprayers | Spot sprayers, small boom sprayers, ATV/UTV/Lawnmower sprayers. | 12-volt Diaphragm Pump |
| Commercial Pest Control Sprayers | Skid sprayers, ride-on applicators, boom sprayers. | Diaphragm Pumps, 12-volt pumps, Roller Pumps |
| Tree Sprayers | Skid sprayers, Truck or trailer mounted. | High-Pressure Diaphragm Pump |
| Agriculture Sprayers | Crop sprayers, Pasture sprayers, boom, and boomless sprayers. | Centrifugal Pumps, Roller Pump |
| De-Ice/Anti-Ice Sprayers | Municipal anti/de-ice trucks, parking lot de-ice sprayers. | Centrifugal pumps |
| Dust Control Sprayers | Water trucks and trailers. | Centrifugal pumps |
How to Size a Lawn & Garden Sprayer
The pump size you need will be determined by the output of your sprayer. There are two fundamental characteristics of a sprayer that you need to measure to determine the pump size: required flow and operating pressure.
Every sprayer will be designed for a specific task. That task will require a certain amount of flow and pressure to make it perform effectively.
Above we listed the different types of pumps used on different sprayers. Now, let’s look at how to determine what flow and pressure you need so you can select a pump that will meet those demands.
Sizing a 12-volt Pump for a Sprayer
12-volt diaphragm pumps are a very common sprayer pump used on small boom sprayers and spot sprayers. If you want to put together a lawn sprayer or sprayer for an ATV/UTV then a 12-volt sprayer will typically provide enough flow and pressure.
12-volt sprayer pump models range from about 1-5 GPM and 30-200 psi. Some 12-volt pumps will reach higher pressures but the flow is generally way too low to be effective for a sprayer pump.
So how do I know if I know what size sprayer I need? Start by adding up the total flow needed to feed all the nozzles on your bone or your spray wand. To calculate this we need to know the size or flow capacity of each spray nozzle on your boom or spray gun/wand.
Example: A lawn sprayer with three nozzles on one boom. Each nozzle flows 0.2 gallons per minute at 40 psi. This means the total flow your boom needs is 0.6 gallons per minute.
It is important to remember that the flow rate of your nozzles will vary at different pressures. The flow rate will increase as pressure increases. So we want to leave some padding to increase your rate if you wish to operate at a higher pressure. You can add about 20% more flow to the total flow required to feed all the nozzles on your boom to provide adequate cushion for this reason.
Agitation and recirculation will also require some flow so add 10 to 20% of your total flow rate. So in this example, we would want a pump that puts out at least 1 gallon per minute if not more to adequately supply the nozzles on the boom as well as cover any increased rate or tank agitation.
You might be wondering why not just select the largest 12-volt pump available and then you’ll have plenty of flow for any circumstance. While this would work, you will be spending more money and it may be harder to dial in the exact pressure you need to achieve your desired flow rate if the pump is much larger than what you need.
This is because most 12-volt sprayer pumps are demand pumps. A demand pump has a pressure switch that turns the motor off at a set pressure. An oversized pump May be subject to cycling on and off without a pressure regulator. If you are new to sprayers be sure to read this article about how to stop 12-volt pumps from cycling on/off.
How Much Pressure Do I Need?
When spraying with a boom the maximum pressure you need is typically no more than 60 psi. Therefore, you don’t need to select a pump that can produce any more pressure than this.
If you were spraying with a spray gun and want to spray long distances of 20-25 feet or more then a pump that can produce higher pressure may be necessary. Spray distance requires a combination of flow and pressure. The nozzle type and size also play a factor.
Sizing a Pump for a Boom or Boomless Sprayer
Whether you need to size a pump for an agricultural, turf, deice, or dust control sprayer, the process is similar to determining pump size for a 12-volt sprayer discussed above.
You must calculate the total gallon-per-minute flow requirement of the boom and then add 10 to 20% to the total to account for spraying at higher speeds or application rates. Also, add 10-20% for agitation or any other sprayer accessories on your sprayer.
Example: A boom with 17 sprayer nozzles. Each nozzle flows 0.8 gallons per minute at 40 psi. 17 x 0.8 gives us a total flow required for the boom of 13.6 GPM. After adding 20% it comes to 16.32 GPM.
In this case, a centrifugal pump or roller pump that will produce 20 GPM or more would be ideal. Larger is ok for a boom sprayer, any excess flow will be bypassed back to the sprayer tank.
Example: A boomless sprayer for dust control with two Boomless sprayer nozzles. Each nozzle requires 40 gallons per minute at 40 psi. This means you need 80 GPM from your pump at 40 psi. When you add in 20% it comes to 96 GPM.
For this boomless sprayer, you would want a pump that is 100 GPM or more. A centrifugal pump will be the only type of pump that will work in this scenario.
How to Size a Pump for A Skid Sprayer.
Selecting the correct pump size for a skid sprayer is different than it is for a boom or boomless sprayer. Not only is flow rate important, but the pressure is also vital. Especially when it comes to spraying trees.
The pump type used on skid sprayers can be either a centrifugal pump, roller pump, diaphragm pump, or piston pump. For spraying trees, you will want a high-pressure diaphragm pump. If you are looking for a tree sprayer, be sure to read this article on how a sprayer can reach tall trees.
Sizing the pump is simple because you just have one nozzle to supply. You need to know how far you want to spray and what combination of flow and pressure will get you there. Then you can select the pump that offers that flow rate at the necessary psi.
The nozzle size and type play a huge part in spray distance. The spray distance or “throw” of a sprayer nozzle will vary with different pressures and flow rates. The nozzle manufacturers can sometimes provide the approximate spray distance that a nozzle can reach at different flow rates and pressure combinations.
I can tell you from research, that to spray 50-foot tall trees you need about 500 psi and 17 gallons per minute. You can find a chart for tree spraying nozzle distances and the flow and pressure required to reach them here.
High-pressure diaphragm pumps are generally the only type of pump that will work in this scenario. You would need a pump similar to the Udor Kappa 75 that will produce 560 psi and 20 GPM.
Conclusion
Pump size is important. A pump too large won’t necessarily cause a problem, but it will cost you more money. It also may require more horsepower and that will also cost money. The most important factor is to ensure that your pump can provide the flow and pressure needed for your sprayer to work effectively.
