Troubleshooting Common Diaphragm Pump Problems: A Practical Guide

How AODD Pumps Work (Quick Overview)

Air-operated double diaphragm (AODD) pumps run on compressed air, driving diaphragms back and forth to move fluid through check valves. Because the design is simple and seal-less, they’re dependable, but they are sensitive to several factors that directly affect performance:

• Air supply pressure and CFM
• Suction conditions (lift, restrictions, air leaks)
• Chemical compatibility and diaphragm materials

Understanding these basics helps narrow down the root cause quickly when a problem occurs.

You can read more about how diaphragm pumps work in our blog dedicated to them, What Is a Diaphragm Pump and How Does It Work?

Common Diaphragm Pump Symptoms and How to Fix Them

1. Pump Cycles Once Then Stops

If the pump cycles once and then refuses to continue, it’s usually a sign that the pump is hitting resistance or something is preventing the air valve from working correctly.

Likely causes include:

• Deadheading (system pressure equal to or higher than air supply)
• Air valve or gaskets installed incorrectly
• Bent or missing actuator plunger

Once you’ve identified the likely cause, you can take the following steps to resolve the issue.

Fixes:

• Increase air inlet pressure within safe limits
• Reinstall or realign air valve gaskets
• Inspect pilot valve and plungers for damage

If the pump restores normal cycling after these checks, the issue was likely installation-related rather than a component failure.

2. Pump Will Not Operate or Cycle

A pump that won’t start at all is most commonly suffering from air-related problems or discharge restrictions. Before assuming a part has failed, it’s worth reviewing the most frequent causes first.

Likely causes include:

• Over-lubrication
• Insufficient air supply (line size, PSI, or CFM)
• Blocked or closed discharge line
• Clogged air exhaust muffler
• Deadhead condition
• Diaphragm rupture causing fluid to enter the air side
• Blocked pump chambers

Working through the list systematically will usually identify the source of the problem.

Fixes:

• Reduce or remove lubrication — most AODD pumps are designed to be lube-free
• Verify compressor capacity and air line sizing
• Check discharge valves and piping for obstructions
• Clean or de-ice the muffler
• Inspect diaphragms and replace if damaged
• Flush or clear blockages in pump chambers

Once air supply and discharge flow are restored, the pump will usually return to normal operation.

3. Pump Cycles but Won’t Prime or Has No Flow

When the pump is cycling normally but producing no flow, the issue is almost always on the suction side. This is one of the most common troubleshooting calls we receive.

Likely causes include:

• Cavitation due to poor suction conditions
• Obstructed or sticking check valves
• Worn or missing valve balls
• Air leaks on the suction side
• Excessive suction lift
• Suction line blockage
• Diaphragm rupture

Addressing suction and check-valve issues will resolve the majority of priming failures.

Fixes:

• Move the pump closer to the product or reduce suction lift
• Clean or replace valve balls and seats
• Check and tighten suction-side gaskets and fittings
• Remove or flush obstructions from suction lines
• Fill chambers with fluid to assist priming if suction lift is too high
• Inspect diaphragms for rupture

Once suction integrity is restored, the pump will usually prime without further adjustment.

4. Pump Runs Sluggish, Stalls, or Has Poor Flow

Sluggish cycling or reduced flow rates are typically the result of air supply problems, suction issues, or restrictions in the system.

Likely causes include:

• Over-lubrication
• Icing of the muffler
• Cavitation
• Low air pressure or insufficient CFM
• Excessive suction lift
• Undersized suction or air lines
• Air leaks or blockages
• Entrained air or vapor lock

Addressing the root cause should be done in the order of simplest to most complex.

Fixes:

• Reduce lubrication
• Clean or de-ice the muffler and consider adding an air dryer
• Check suction conditions and reduce restrictions
• Verify compressor air volume and pressure
• Resize suction or air lines if too small
• Purge trapped air using chamber vent plugs (with caution)

Most performance issues can be resolved once air supply and suction conditions are corrected.

5. Product Leaking Through the Air Exhaust

This is a clear indication that something internal has failed and requires immediate attention. Fluid in the air exhaust is always a sign of diaphragm issues.

Likely causes include:

• Diaphragm failure
• Loose diaphragm plates
• Chemical or temperature-related material failure

Correcting this problem involves replacing compromised parts and preventing further damage.

Fixes:

• Replace diaphragms immediately
• Ensure plates are installed correctly and tightened
• Check chemical compatibility for the fluid being pumped

Never continue running a pump that is leaking product into the air side.

6. Premature Diaphragm Failure

Diaphragms are wear parts, but they should still offer reliable service life. If they’re failing early, something in the system is putting them under stress.

Likely causes include:

• Cavitation
• Excessive flooded suction pressure
• Incorrect diaphragm material for the application
• Incorrect installation or worn plates

Reviewing installation conditions is usually the best place to start.

Fixes:

• Increase suction pipe diameter or reduce suction restrictions
• Raise the pump position to reduce inlet pressure where needed
• Select a diaphragm material compatible with your fluid
• Check plate condition and installation direction

Once matched to the right material and installation setup, diaphragm life should improve significantly.

7. Unbalanced Cycling

Uneven or unbalanced cycling often indicates a problem on the suction side or an issue with the check valves.

Likely causes include:

• Excessive suction lift
• Undersized suction line
• Suction air leaks
• Worn or obstructed check valves
• Entrained air in the product

Correcting suction and check-valve issues typically resolves unbalanced operation.

Fixes:

• Improve suction conditions
• Match suction line size to pump connections
• Tighten gaskets and pipe unions
• Clean or replace check valves
• Purge air from chambers where safe to do so

Once flow conditions are equalised, the pump should return to smooth, even cycling.

How to Prevent Most Diaphragm Pump Problems

Good installation and regular maintenance play a huge role in keeping diaphragm pumps running smoothly.

• Use correctly sized suction and air lines
• Ensure air supply meets both PSI and CFM requirements
• Choose the right diaphragm material for the fluid
• Keep suction lines short and free from restrictions
• Install strainers to prevent debris entry
• Monitor early signs like uneven cycling or muffler icing

By following these practices, you can dramatically reduce downtime and extend the life of your pump.

Need Help?

If you’re unsure what’s causing the issue, or you need replacement parts, the team at TF Pumps is always happy to help. We can assist with troubleshooting, parts identification, and selecting the right pump for the job. Contact Us or fill in the form below, and one of our team will contact you.

Additional Reading

What Is a Diaphragm Pump and How Does It Work?
Winter Pump Maintenance: Protecting Your Pump from Cold Weather
How To Select The Right Diaphragm For Your Application
Graco AODD Troubleshooting