When you pull out your sprayer you expect it to work, but sometimes sprayers don’t perform after they haven’t been used in a while. If you have a roller pump on your sprayer it can be very frustrating when everything seems fine with the pump but you are not getting the flow or pressure you need.
Roller pumps are simple in design small things that might not be noticeable can cause poor performance. So to help you get back up and running, let’s examine the aspects of a roller pump and how to troubleshoot them.
How a Roller Pump Works on a Sprayer
When installed on a sprayer, a roller pump is driven by an engine, motor, or PTO. This spins the rotor which in turn forces the rollers around the outer edge of the pump housing. Water is gravity into the pump inlet and the rollers push it along the small cavity between the rollers and the pump housing. At high RPM this action creates high flow and pressure.
I have a more detailed explanation and a diagram of how a roller pump works in this post about different sprayer types.
Installing a Roller Pump Correctly
Before covering specific troubleshooting, it is important to make sure that the pump has been installed correctly. Roller pumps are versatile pumps that can be used on different sprayer types and are often used when people want to build a simple sprayer. If you are working on a homemade sprayer, check these aspects of the installation:
- Suction hose: Ensure that a reinforced suction hose is used on the pump inlet and that it is adequately sized. View specific details on the roller pump hose size needed for each roller pump model in this post on installing sprayer pumps.
- Pump Rotation & RPM: There are different roller pump models made to be used with different drive types and shaft rotations. Check to ensure the pump is being driven in the correct direction. Refer to this article on hooking up sprayer pumps for exact details.
These are important factors that can affect the pump’s performance, and longevity, and if not installed correctly this can lead to quick pump failures. Now on to the troubleshooting guide.
Roller Pump Trouble Shooting
Roller pumps are relatively simple pumps. There are not too many moving pieces, so troubleshooting is straightforward. That being said, small changes in the pump or sprayer can be hard to notice without some specific inspection and testing. Here are the main issues and what to check.
Issue: Roller Pump Won’t Prime
Possible Cause #1: Leak in the suction hose
This is probably the most overlooked cause of pump failure because it is impossible to see small cracks or connection points that are letting air get drawn into the suction plumbing.
If your pump will not prime examine all the plumbing connections. Use pipe thread sealant to ensure that the connections are air tight. Inspect the hose, pipe, strainer, and any valves for cracks. Ensure that the o-ring in your strainer bowl is sealing properly. Check all the hose clamp connections.
Also, remember from earlier that the suction hose needs to be a reinforced hose that withstands suction.
Possible Cause #2: Obstruction/Plug
While it is not likely that your suction hose or pipe becomes completely blocked or plugged, over time herbicide and fertilizer residue can build up and cause problems. It is more likely that this is an issue with the strainer screen or the tank outlet.
Check your strainer and clean it out. If your tank outlet has an anti-vortex or a screen on the end of the suction hose that drops in the tank, check those or plugs/debris.
Possible Cause #3: Rollers Damaged/Stuck
The rollers in the pump can get stuck. Especially if the pump has not been operated in a while and may not have been flushed out. Many roller pumps are cast iron and they rust, rust equals friction and may interrupt the movement of the roller.
Rollers can also break into pieces if they are old or not compatible with the liquid being pumped. When this happens the pieces get stuck downstream in the sprayer potentially leading to other issues.
To determine if it is rollers, open the pump and inspect them. If they are stuck, a little 4D-40 can help if the pump is rusty. Replace cracked or damaged rollers.
Possible Cause #4: Bad Seal
There is a shaft seal on both sides of the pump and a housing o-ring. If these are shot the pump may fail to prime. To check you can force feed/gravity feed water to the pump inlet and see if there is a leak as you turn the shaft. Replace the seals if needed.
Possible Cause #5: Pump housing/Rotor wear
After a certain amount of use, a roller pump housing wears down to the point where there is too much space between the wall of the pump housing and the rollers so no water gets pushed through by the rollers.
How Do I Know If My Roller Pump Is Bad?
If your pump is not priming, it may be beyond repair. To tell if your pump is bad, you need to take the pump apart and inspect the inside of the pump housing. If you notice a lip or ridge on the edge of the inside pump housing. This is a sign of extreme wear and your pump may not prime. The rotor thickness will also wear thin over time. If the rotor is worn below the necessary thickness then the pump will not work.
This video shows how to inspect a roller pump for wear:
Issue: Low Pressure
Possible Cause #1:
Low pressure, if a pump issue, is usually caused by the same type of issues that can cause a pump to not prime. You might not notice these issues if your pump has flooded suction. But if you experience a loss of pressure from your sprayer and you have not recently adjusted the pressure regulating valve or changed the nozzles on your sprayer then check these things:
- Suction hose, cracks, kinks, clogs
- The strainer is clogged, o-ring is not sealed
- Pump seals bad
- Pump rotor or housing wear
Possible Cause #2: New Spray Nozzles
Changing to a larger spray nozzle without adjusting the pressure regulating valve can result in lower system pressure. If you have recently changed your spray nozzles to a larger size this may be the cause.
These are the most common issues that can cause a roller pump to fail. A thorough inspection is key to finding the issue and eliminating all possible causes.
Roller Pump FAQs
In addition to troubleshooting a roller pump, you might have other questions when installing it or deciding on other ways you can use the pump. Here are some common questions about roller pumps.
Can a roller pump run dry?
You should not run a roller pump dry. If you operate a roller pump with no liquid being supplied to the pump, the internals will get too hot. The rollers can melt and the seals will fail.
For more information read this article about what it means to run a pump dry.
How do you clean a roller pump?
Roller pumps should be flushed with fresh water and a sprayer cleaner/neutralizer like ammonia or a product like Blazer should be used to remove chemical residue.
What is the difference between a centrifugal pump and a roller pump?
A centrifugal pump is not a positive displacement pump like a roller pump. A roller pump uses mechanical action to physically push liquid while a centrifugal pump relies on centrifugal force. Roller pumps generally develop higher pressure and are available in limited sizes. Centrifugal pumps can be created as large as necessary as long as there is horsepower enough to drive them.
Roller pumps do require pressure relief on the discharge side for safety. When they are dead-headed, they develop pressure in the line that may burst hoses or fittings. A centrifugal pump will only reach a certain pressure before hitting its max. They don’t require pressure relief, although it is not a bad idea to still have it in place.
Are roller pumps self-priming?
Most roller pumps do have the ability to self-prime. They are however limited in the distance and height they can draw water. For the most efficient and best practice, limit the suction lift of a roller pump as much as possible. Gravity feed the pump if possible.
Final Word on Roller Pumps
Roller pumps are useful sprayer pumps that offer more pressure than most centrifugal pumps. If you follow these guidelines and troubleshooting points, you can keep your roller pump working great.