Diaphragm Pump Not Working: Complete Troubleshooting Guide

If you are reading this then chances are you are frustrated. Your diaphragm sprayer pump was working fine last time you used it and now it won’t develop any pressure, or it won’t pump at all, or maybe something else. Whatever is going on, you want to identify the problem, fix it, and get back to work. That being said, let’s get to it.

Diaphragm Pump Troubleshooting Overview

Just so we are all on the same page we will briefly cover the specific type of pumps we will be looking at in this article. We will also go over some basics, so if you are experienced at operating these pumps, feel free to jump ahead to the more specific pump issues. 

In this article, we will focus on medium-pressure diaphragm pumps like the popular Hypro D30. The content will largely be applicable though to several different models from Hypro, AR, Udor, Comet, and other manufacturers.

In a previous article, I discussed troubleshooting a skid sprayer. Diaphragm pumps are commonly used on skid sprayers, so there will be some overlap with that article. 

Diaphragm sprayer pumps are extremely common in agriculture, turf care, tree spraying, and other industries. They are known for their ability to handle viscous liquids while producing the flow rates and pressures needed to propel liquid great distances. 

How a Diaphragm Pump Works

A diaphragm pump is a type of positive displacement pump that uses flexible diaphragms to move fluids. These diaphragms are connected to a piston and shaft. A diaphragm pump may have two or more diaphragms/pistons working together to create the pumping action. 

You’ll find a more detailed breakdown of the parts and how it operates in this article about different sprayer pumps.

Diaphragm Pump Diagram & Components

A diaphragm pump has multiple moving pieces but these are the main ones:

  • Check valves
  • Pistons
  • Crankcase
  • Diaphragms
  • Driveshaft
  • Control unit/Regulating valve

The diaphragms are located on the top of each piston. For each piston and diaphragm, there is an inlet and outlet check valve. One valve opens to let liquid in when the piston is on its down stroke, and when the piston is on the upstroke it pushes liquid out the outlet check valve. All the pistons work together to create a constant flow of liquid. 

Guide to Troubleshooting Your Diaphragm Pump

IssuePossible CausesSolution
Low or no pressureAir leak in the suction plumbing, Suction hose collapsed, Plug in suction hose or filter, Damaged relief valve, damaged/improperly installed check valvesClean out the strainer. Inspect all the fittings, connections, hose, clamps, etc. on the suction size. Inspect check valves. Force feed pump inlet to test relief valve.
Pressure flucuatesAir leak in suction plumbing, Air trapped in the pumpInspect suction plumbing. Run pump with open discharge to release air.
Pump won’t primeAir leak in suction plumbing, Check valve installed incorrectly or damagedForce prime the pump and see if it works. Inspect check valves. Replace hose if cracked, clean strainer, inspect suction plumbing for weak connections.
Pressure drops when opening gun or valvesPressure fluctuatesCheck the relief valve setting, and replace it if necessary. Reduce the nozzle size to be within the range of the pump’s output capability.
No oil/Won’t hold oil in resiviorDiaphragms badReplace diaphragms and change the oil
Oil has milky colorDiaphragm split, damaged, or wornReplace diaphragms and change the pump oil
Diaphragms keep wearing out prematurleyDiaphragm material not compatible with chemical, Not in bypass when starting pump, Pump not flushed out after useRefer to the pump manual for proper startup procedure. Check that the liquid being pumped is compatible with the diaphragm material. Flush pump with tank cleaner when stored for more than a few days.

Suction Plumbing Issues

Most issues with diaphragm pumps can be traced back to the suction plumbing. This includes the entire fluid path from the tank to the pump inlet. It cannot be overstressed how crucial it is to maintain solid connections that are airtight and use a suction hose that is reinforced and will not collapse. 

Tips to Identify the Cause of Diaphragm Pump Problems

Start with the pump driver. Whether gas-engine, PTO, or some other motor, ensure the driver is running at the required rpm and that it is properly connected to the pump. This will eliminate the engine/drive as the issue.

Next, you can force prime the pump to ensure that the regulating valve and the pump itself is operating normally. Use an external water tank if necessary. Make sure the tank outlet is above the pump inlet and water is flowing freely from the tank into the pump. Run the pump and adjust the control unit from bypass to the other settings to see if it is functioning. The pressure from the spray gun should change accordingly as you adjust the control valve.

If the pump and regulating valve perform correctly when force primed, then it is almost certainly a suction plumbing issue. Examine all the suction plumbing and replace components as needed. 

If the pump does not perform when force primed, then the regulating valve may need to be replaced, but first, check that the check valves are not plugged or damaged and that they are seated properly. There is typically an inlet and outlet check valve for each piston/diaphragm. They will be installed in opposite directions. 

It is also important to consider the system or sprayer that the pump is being used on. In addition to the suction plumbing, other changes in the overall system can lead to the pump performing differently even though nothing is necessarily wrong with the pump. 

Diaphragm Pump FAQs

Can You Run a Diaphragm Pump Dry?

Yes, one of the advantages of diaphragm pumps is that they can run dry temporarily without suffering damage. This is because the moving components inside the pump are lubricated with pump oil. However, it’s important to note that while these pumps can run dry, it’s generally not recommended for extended periods of time. Prolonged dry running can cause increased wear to the pump’s internal components, potentially shortening its overall lifespan.

What happens if you deadhead a diaphragm pump?

Deadheading a diaphragm pump refers to a situation where the pump’s discharge is closed off while the pump continues to run. This can occur if a valve on the discharge line is closed or a hose is blocked downstream of the pump.

If the pump is deadheaded and there is a regulating valve installed it will open and bypass liquid to the tank assuming the valve or block causing it to be “deadheaded” is downstream of the regulating valve.

If there is no regulating valve or the valve is not operating correctly and the pump is dead-headed it can lead to catastrophic failure. Diaphragm pumps are positive displacement pumps which means that they will continue to push liquid and build pressure even when the outlet is blocked. 

Hoses, fittings, valves, or any component that is not rated to handle this increased pressure can break. These breaks can be dangerous with components potentially becoming projectiles.

It is important that a diaphragm pump, or any positive displacement pump for that matter has an adequate relief valve installed to protect against any potential overpressurization or a “deadhead” scenario.

Are Diaphragm Pumps Self-Priming? 

Yes, Diaphragm Pumps are self-priming. They can create and maintain a sufficient vacuum level to draw fluid into the inlet. However, there is a limit to the height that the pump can be above the liquid level and still maintain an effective prime.

It is also important to note that while these pumps are self-priming, they will prime faster and operate more efficiently with shorter suction distances. Also, remember to ensure that the suction line is airtight, as air leaks can hinder the pump’s ability to self-prime effectively.

Diaphragm Pump Maintenance

Diaphragm pumps are like any other piece of equipment. Without proper maintenance, they will not last as long as they otherwise could. It should also be noted that pumps will have a varied life span relative to the work it is doing. If it is used daily to pump abrasive liquids it will likely need new diaphragms and oil more often.

The pump oil needs to lubricate the crankcase. Oil level and oil color should be monitored whenever the pump is being used. The diaphragm separates the oil from whatever liquid the pump is transferring. If the diaphragm is bad or cracked the oil will get milky or the oil level can drop.

It is a good practice to rinse the system with fresh water after each tankful or whenever the pump will be stored for more than a few days. In the off-season/winter, the pump should be winterized. This means completely draining the system, rinsing it, and then filling the tank with antifreeze/water solution. The antifreeze should be circulated through the entire system and kept in it while it is stored.


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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