When you go Shopping for a backpack sprayer you will notice that there are two basic types of Backpack sprayers: piston and diaphragm. Learning the difference between these types Will help you select the backpack sprayer that is right for you.
To thoroughly answer this question at only did I do some extensive research but I also purchased one of each type of backpack sprayer so that I could test and compare them.
Piston And diaphragm backpack sprayers differ in the type of mechanism that is used to develop pressure in the sprayer. A Piston-style backpack sprayer uses a solid piston, while a diaphragm-style backpack sprayer has a flexible diaphragm. Generally, the piston style is capable of producing higher pressure while the diaphragm style is better suited for handling suspended solids in the liquid.
The important question is which version is right for you? There are several factors to consider, and in the rest of this post we will unravel this mystery
RELATED: Solo Backpack Sprayer Frequently Asked Questions
The Key Difference Between a Diaphragm & Piston Backpack Sprayer
When it comes to manual backpack sprayers there are two different options: piston pump or diaphragm pump. These two types of backpack sprayers are generally the same when it comes to the tank, the hose, and the spray wand. The only difference is in the design of the pump mechanism.
Simply put a Diaphragm Backpack sprayer has a flexible diaphragm pump assembly and a piston-style backpack sprayer has a piston pump assembly. Both of these develop pressure when the handle of the backpack sprayer is “pumped”. This subtle difference does result in A few variations and benefits for each backpack sprayer.
Next, let’s take a closer look at how each one works and how this affects performance. But, before we get into it. I am using Solo backpack sprayers for this test and comparison. They have worked well for me for years. You can see my full review of the Solo Diaphragm Backpack Sprayer here.
How a Piston Pump Backpack Sprayer Works
Piston backpack sprayers operate using a piston within a cylinder. As you manually work the pump lever, the piston moves up and down, creating pressure that forces the liquid out of the sprayer. This process builds up pressure in the tank, pushing the liquid up through the supply line to the spray wand. When the valve is opened, the pressurized liquid is ejected through the nozzle.
How a Diaphragm Pump Backpack Sprayer Works
Unlike their piston counterparts, diaphragm backpack sprayers use a flexible diaphragm to create pressure in the tank. This diaphragm, functioning somewhat akin to the human diaphragm in our chests, contracts and relaxes to propel the liquid through the system. As you pump the lever, the diaphragm’s movement generates the necessary pressure to send the liquid up a supply line, eventually exiting through the wand when the handle is squeezed
Benefits of a Piston Backpack Sprayer
- Greater maximum pressure:
- this means she can potentially spray a stream of liquid further than with a diaphragm pump.
- Greater pressure means longer spray time as well. You will be able to spray more before the pressure inside the sprayer drops to a level that does not produce a consistent spray pattern any longer
- This also means that there is potential for using larger nozzle sizes and spraying a greater volume Of liquid over a given time
Benefits of a Diaphragm Backpack Sprayer
- Flexible diaphragm
- This means that the pumpkin compresses liquid into the pump chamber that has suspended solids in it without damaging the pump assembly.
- The diaphragm is more flexible resilient residue built up inside the pump assembly or over whatever does not result in pieces breaking. Because the diaphragm has some give
By the way, if you are looking for more help selecting a backpack sprayer, check out our Backpack Sprayer Buyers Guide
How Do Piston and Backpack Sprayers Differ in Performance?
I have used a diaphragm pump style for years, but I recently purchased a piston-style backpack sprayer to compare them. I also wanted to see how accurate the manufacturer’s specs were when it came to maximum pressure and spray distance. So of course I did a few tests.
If you are considering a backpack sprayer but aren’t quite sure if one is right for you, please read my post on “Are Backpack Sprayers Worth It” to help you decide.
Maximum Pressure
Solo lists a maximum pressure for both their diaphragm and pitstop backpack sprayers. They claim the piston style can reach 90 psi of the diaphragm style can reach 60 psi.
I wanted to see how accurate this was and get a sense of what the actual pressure is at the spray nozzle as you spray. Because you aren’t always gonna be spraying at the maximum pressure. As soon as you pull the trigger the pressure is going to go from the maximum decrease. Spray pattern changes from this decreased pressure you will have to start pumping the sprayer again.
To test this I got an adapter and a cap so I could attach a pressure gauge to the end of the spray wand. Here are the results I got for pressure:
Piston pump type: 89 PSI
Diaphragm pump type: 60 PSI
The actual measured pressures were about spot on to what the manufacturer advertises. I could get a little more pressure out of each backpack sprayer but I would not recommend it. This may damage the sprayer.
Spray Distance
The “reach” or spray distance is an important factor when you want to accomplish certain tasks. For example, spraying branches in trees or cleaning a rooftop.
The difference in maximum pressure between these two sprayers would lead me to believe that the Piston pump would be able to spray a further distance. This was true but the diaphragm pump was not far behind.
I mimicked a test that I did with a hand pump sprayer. I waited for a still day (mostly still anyway, there is really no such thing where I live) and set out a tape measure on a flat open area of my yard. Then I pumped each sprayer until it was fully pressurized according to the manufacturer’s instructions. Then I held the spray wand with the nozzle horizontal to the ground. This was about five feet above ground.
Results of The Spray Distance Test Piston and Diaphragm Backpack Sprayers:
| Piston Type Backpack Sprayer | Diaphragm Type Backpack Sprayer | |
| Farthest Spray Distance | 24 ft | 20 ft |
| Effective Spray Distance | 20-21 ft | 17-18 ft |
In this chart, I show the “furthest spray distance” which is the furthest distance that I could see droplets on the tape measure. The “effective spray distance” is the range where the majority of the droplets fell. This is a better indicator of how far the backpack sprayer could actually provide enough coverage for effective results.
Spray Time
The next function of the sprayers that I tested was the duration of the spray time. In other words, how long will the sprayer maintain a functioning spray pattern when you pump the sprayer to its maximum pressure?
What I sought to find here was how much pumping each backpack sprayer requires as you spray. So again, I set up a little test. I pumped each sprayer until the lever was hard to move, then I pulled the trigger and started my stopwatch.
Comparing the Spray Time of Piston and Diaphragm Style Backpack Sprayers
| Piston Type Backpack Sprayer | Diaphragm Type Backpack Sprayer | |
| Spray Time | 2 Minutes, 7 Seconds | 2 Minutes, 38 Seconds |
| Effective Spray Time | 35 Seconds | 25 Seconds |
I recorded the total time that water came out of the nozzle before it was just a drip. This information is not really that valuable because most likely, you are going to start pumping again long before you let the pressure drop that low.
So as I sprayed I observed the spray pattern. I recorded the time it took before the spray pattern started to weaken to the point where it would not offer much coverage. This is a bit subjective, but basically, it was the point that I would start “pumping” the handle again.
One important difference that I observed was the amount of pumping that it took to get the sprayer up to the maximum pressure. The diaphragm style takes less pumping to get the sprayer fully pressurized (to the point the handle almost won’t move and you don’t want to over-pressurize and break anything). The piston pump takes a lot more pumping before it won’t build any more pressure, almost 20 strokes. With the diaphragm pump sometimes it only took six or seven strokes.
The main takeaway is that the piston pump sprayer offers a bit more effective spray time before you need to pump the handle, however, it takes a lot more pumping to get back up to full pressure. The overall findings lead me to choose a diaphragm-style backpack sprayer over the piston style.
Sprayer Output
The difference in pressure and spray time will result in the piston sprayer applying more liquid in a given amount of time than the diaphragm sprayer. This is assuming you are using the same nozzle. This means that you can potentially cover more ground with the piston sprayer if you walk at a faster pace.
The difference in sprayer volume affects calibration and how much area you can cover. You can see a full explanation in this guide on how much area you can cover with a backpack sprayer.
Piston or Diaphragm Backpack Sprayer: Which One is Right for Me?
It’s great to see these differences on paper but how do these differences affect the results you get? Which one is better for me?
Based on the testing that I did, I would choose a diaphragm-style backpack sprayer. This type does not spray quite as far but the other aspects of the sprayer provide several advantages over the piston style.
Diaphragm Style Backpack Sprayer Advantages
- The flexible diaphragm pump is more forgiving against chemical sludge and residue
- The diaphragm handles wettable powders, and suspended solids in liquid better
- Less “pumps” of handle to reach maximum pressure
Piston Style Backpack Sprayer Advantages
- Spray reach is about 3-4 feet more than diaphragm style
- A higher volume of liquid can be applied in the same amount of time as the diaphragm pump style
Although the diaphragm backpack sprayer does not spray quite as far, I don’t see the extra 3-4 feet of spray distance as enough of an advantage. This is because the flexibility of the diaphragm is much more resilient to the chemical residue and any debris that may be suspended in the liquid.
It also takes a lot less work to “pump” the sprayer up to its maximum pressure. This means less fatigue over a long day of spraying.
Both of these types of sprayers are subject to wear and tear. Proper cleaning and maintenance is key. You can learn more in this article that breaks down all the things to do when a backpack sprayer won’t work properly.
When to Use a Piston-Type Backpack Sprayer
If you are going to be needed to spray as far as possible, then the piston style does offer a little more spray “reach”. If you want to put on a heavier dose of liquid over a given area, the piston sprayer does push liquid through the same size nozzle faster than the diaphragm-style sprayer.
This means that if the nozzle is the same, and you walk at the same speed, you will be applying more liquid per square foot when using the piston-style sprayer. There are many variables to the rate you apply, for a more detailed breakdown, read this guide on how much area a backpack sprayer can cover.
The amount of liquid that will come out of the nozzle in a given amount of time will vary depending on how much you “pump” the sprayer, but if you keep it pumped up a piston pump will disperse more than the backpack sprayer due to the higher maximum pressure (assuming the same nozzle size).
When to Use a Diaphragm-Type Backpack Sprayer
As mentioned earlier, the diaphragm-style backpack sprayer is my personal choice. I prefer it because one of the major failures of a backpack sprayer is the pump assembly. A piston pump can “lock” up if chemical residue builds up. This can be limited by flushing out the sprayer and cleaning it, but some chemicals are more aggressive than others and it is only a matter of time.
The diaphragm in the pump assembly can wear out and tear if it is “over-pumped”, but due to its flexible nature, there is more forgiveness than a piston-style pump.
