Air-operated double diaphragm (AODD) pumps are known for their reliability, versatility, and ability to handle everything from clean water to thick slurries and aggressive chemicals.
But even the most robust AODD pump can stall unexpectedly — stopping mid-operation, refusing to restart, or pulsing weakly despite full air supply.
If your AODD pump is stalling, here are the most common causes and how to fix them.
1. Insufficient Air Supply Pressure or Volume
AODD pumps rely entirely on compressed air. If the pressure or flow rate drops below operating requirements, the pump may stall, pulse slowly, or fail to cycle altogether.
Check for:
- Low plant air pressure (below the pump’s minimum spec)
- Undersized airline or filter/regulator setup
- Blocked or restricted air hose
- Shared air lines with competing demand
Solution:
Ensure your compressor can supply both the required pressure and CFM for your pump size. Use a dedicated airline, and make sure filters and regulators are clean and appropriately sized.
2. Ice Formation in the Air Exhaust
As compressed air expands in the pump’s exhaust chamber, it cools rapidly — especially in humid environments. This can lead to ice formation, blocking the air path and causing the pump to stall.
Signs include:
- Pump runs fine, then gradually slows and stops
- Ice forming around muffler or exhaust
- Resumes operation temporarily after stopping
Solution:
Install a moisture separator or air dryer upstream of the pump. In extreme cases, consider using a heated or insulated muffler.
See blog here about how to stop freezing of air diaphragm pumps.
3. Worn or Damaged Air Valve
The air valve (also known as the pilot valve or shuttle valve) controls the direction of compressed air to alternate diaphragm strokes. If it becomes sticky, worn, or contaminated, the pump can hang up at the end of a stroke.
Look for:
- Pump stops in mid-cycle
- Intermittent or uneven pulsing
- Clicking sound stops
Solution:
Disassemble and inspect the air valve. Clean out any dirt, oil, or debris, and replace worn O-rings or seals. If badly worn, replace the entire valve assembly. Use clean, lubricated air if your pump model allows it.
4. Diaphragm or Check Valve Issues
Internal fluid components can also cause stalling if they’re torn, warped, or incorrectly installed.
Symptoms:
- Pump runs dry but stalls under load
- No fluid movement despite air cycling
- Unusual noise or vibration
Solution:
Check diaphragms, balls, and seats for wear or chemical damage. Make sure all components are seated correctly and free of debris. Replace if any signs of fatigue or chemical attack are visible.
5. Dead Heading or Blocked Discharge
If your pump has no place to send fluid — due to a closed valve, clogged line, or full tank — it may “dead head” and stall. AODD pumps are forgiving in this scenario, but will not cycle until the backpressure is relieved.
Solution:
Check downstream valves, filters, or discharge piping for restrictions. Install a pressure relief valve or bypass loop if frequent dead-heading is part of your process.
Bonus Tip: Prime It Properly
On initial startup, some AODD pumps require a few seconds of unrestricted operation to properly prime. If you throttle the air or close valves too soon, the pump may stall before it builds momentum.
Always start with discharge valves open and full air pressure until fluid starts flowing.
Final Thoughts
AODD pumps are tough, but like any mechanical device, they need the right conditions to operate smoothly. If your pump is stalling:
- Start with air supply
- Then check exhaust freezing
- Followed by air valve and diaphragm condition
- And always confirm your discharge path is clear
Still having issues? The Pump Expert can help diagnose the problem — contact us.
