Sprayer Pump Leaks: The Causes & Fixes

The site of water dripping from your sprayer pump can give anyone anxiety. Pumps are great at moving liquid, but when they start to leak, it creates a mess and keeps you from getting work done. The trouble is that finding out why the pump is leaking can be tricky. So why do sprayer pumps leak?

When it comes to Leakey sprayer pumps, there are many possible causes. The primary reason that Sprayer pumps leak is that the o-rings, gaskets, and other mechanisms that provide a seal between the housing and around the drive shaft fail.

These failures can be the result of many different factors, including normal wear and tear, chemical incompatibility, excessive heat, improper installation, or missing pieces. The exact seal or component that might be leaking also depends upon the type of sprayer pump that you have.

In this post, we are going to look at several different types of sprayer pumps and examine why they leak And what to do about it.

Why Do Sprayer Pumps leak?

Sprayer pumps can league for many different reasons. As mentioned earlier, the Primary reason a pump leaks is due to seal failure but there are other possible reasons as well. The potential cause of the leak can vary depending on the type of pump that is on your sprayer. 

Let’s first look at some common reasons for sprayer pump leaks. Many of these are simpler to address than replacing a seal or gasket in a pump. So it’s good to eliminate these as The possible culprits before you tear into your pump.

  • Cracks in the pump housing
  • Damaged O-rings
  • O ring or gasket are improperly seated
  • Seal warped or melted from heat
  • Inlet and outlet fittings are not tightly connected
  • Damaged hose feeding the pump
  • Pitted/damaged shaft
  • Damaged bolts or screws

All pumps have a series of moving parts inside. Working together these components move liquid. These moving parts are driven by a shaft that is powered by an external source. To keep the fluid from leaking out there needs to be a seal or some mechanism that prevents water from leaking out around the shaft or from the seams between different components of the pump. 

Different pumps Utilize different types of seals. Here are the main families of sprayer pumps and the different types of seals that they have. 

  • Centrifugal Pumps: mechanical shaft seal, casing/housing gasket or o-ring
  • Roller Pumps: lip seals, body o-rings
  • High-pressure diaphragm pumps: diaphragms, housing O-rings
  • 12-Volt Diaphragm Pumps: diaphragm plate

Why Do Centrifugal Pumps Leak?

Centrifugal pumps have a simple design. The pump housing typically has a large single gasket or o-ring sealing the two halves of the pump housing. Around the driveshaft, there is a mechanical seal made up of two seal faces and a spring. 

One face of the mechanical seal turns with the shaft, while the spring behind the other face pushes the two seal faces together. This ensures that no liquid can leak out around the shaft. A mechanical seal will begin to leak if it is damaged or worn out. If you have a leak around the shaft or between the pump and the motor/engine that is driving it, it is most likely the mechanical seal. 

RELATED: Troubleshooting a Centrifugal Sprayer/Transfer Pump

There are a few different ways that the seal can become damaged:

Normal Wear

Mechanical shaft seals experience wear over time due to being in operation. The friction between the seal faces will eventually reduce the seal face’s ability to maintain the necessary tightness between them, leading to a leak. Exposure to abrasive particles present in different liquids can result in more rapid wear on the seals.

Seals do not last indefinitely. They have a finite service life and need to be replaced periodically. The life of the seal depends a lot on the liquid being pumped and operating conditions. In some scenarios, a seal may last many years, while in others it only lasts months. 

Incompatible Seal Materials

Chemical compatibility is another major factor with mechanical seals in a sprayer pump. If a seal is not constructed of materials suited to handle the fluid being pumped, the seal will not work for very long. It is important to consult pump manufacturers or chemical companies for help in finding the best type of seal for your pump. 

Run Dry/Cavitation

One of the most common causes of premature seal failure is operating the pump without sufficient fluid. This is known as running the pump dry. This can happen in a few different ways. 

First, you can start the pump with no liquid in it. The seal gets hot from friction and nothing to lubricate or cool it. If the pump is run this way with no liquid, it doesn’t take long and the seal will melt, warp, crack, etc. Then it will no longer keep the pump from leaking and will need to be replaced.

Second, if you run the pump with no liquid for a short period and then supply it with water, the seal will be very hot. The introduction of cool (ambient) liquid will “shock” the seal and it can crack. 

Finally, a pump can “run dry” even when liquid is being supplied to the pump. This happens when there is a restriction preventing adequate liquid from getting to the pump, or there is air getting into the pump. The pump will cavitate due to a lack of liquid and cavitation can cause damage to the seal as well as the impeller. 

If you desire a more detailed breakdown of this, refer to this article about what it means to run a pump dry

Why Does a Roller Pump Leak?

Roller pumps do not have mechanical seals. Instead, there is a lip seal on each side of the shaft that runs through the pump. These seals can wear out over time. Roller pump seals are subject to damage if the pump runs dry and overheats. If there is a leak or drip around the saft it is likely the lip seals.

The pump case is made of two halves that fit together. There is an o-ring between them to provide a seal. If your pump has a drip or leak around the pump casing, then it is typically the body o-ring. If you take apart the pump to replace the rollers, you should check the o-ring. If it is swollen or damaged, replace it. Make certain that you seat it back into place to seal it properly.

Why Do Diaphragm Pumps Leak? 

Diaphragm pumps are more complicated machines than centrifugal and roller pumps. They have more moving parts and different locations for potential leaks. They also operate at much higher pressures which can lead to potential leaks if there are any damaged components. 

Diaphragm pumps typically do not like the product that’s been pumped due to its design. Instead, the fluid can leak into the pump crankcase. 

The drive shaft of a diaphragm pump moves pistons in a crankcase. The crankcase is filled with oil to lubricate the pump as it operates. These pumps use diaphragms to separate the fluid being pumped from the oil in the crankcase. If the diaphragms are worn out or damaged the liquid being pumped will leak into the crankcase oil. When this happens The diaphragms need to be replaced. 

You can find more details in this article that breaks down normal diaphragm pump maintenance and repair. 

12 V Diaphragm Pumps

12 V diaphragm pumps are a very common sprayer pump used on smaller sprayers. Usually, their housings are made of plastic And these can crack when bumped or when the liquid inside freezes. It is common for the inlet and outlet ports to crack from over-tightening the hose connections. 

The pump is sealed up by a diaphragm assembly that has a lip around the outside acting as an O-ring for the housing. This time frame assembly breaks down or is damaged by a chemical attack it will lose its shape and the pump can begin to leak. 


There are many reasons why a sprayer pump could leak. Identifying the leak’s cause is the first step to fixing it. Fortunately for many sprayer pumps the cause of The leak is generally isolated to one area. This is especially true for centrifugal pumps with mechanical seals. 


I have more than a decade of experience using, building, studying, and testing sprayers in several applications. With the knowledge I have gained I want to provide straight forward and detailed answers for DIY homeowners, farmers, and commercial turf and tree care pros.

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